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BROWSE VOLUME

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May 2009

Volume 16, Issue 5,  Articles (05xxxx)


Cover image from F. Girard, M. Primout, B. Villette, Ph. Stemmler, L. Jacquet, D. Babonneau, and K. B. Fournier, Phys. Plasmas 16, 052704 (2009).

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LETTERS

Formation of a localized acceleration potential during magnetic reconnection with a guide field

J. Egedal, W. Daughton, J. F. Drake, N. Katz, and A. Lê

Phys. Plasmas 16, 050701 (2009) (4 pages)

Online Publication Date: 1 May 2009

Full Text: PDF (607 kB)

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Magnetic reconnection near the surface of the sun and in the Earth's magnetotail is associated with the production of highly energetic electrons. Direct acceleration in the reconnection electric field has been proposed as a possible mechanism for energizing these electrons. Here, however, we use kinetic simulations of guide-field reconnection to show that in two-dimensional (2D) reconnection the parallel electric field, E|| in the reconnection region is localized and its structure does not permit significant energization of the electrons. Rather, a large fraction of the electrons become trapped due to a sign reversal in E||, imposing strict constraints on their motions and energizations. Given these new results, simple 2D models, which invoke direct acceleration for energizing electrons during a single encounter with a reconnection region, need to be revised.
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52.30.Cv

Nested multilayered X pinches for generators with mega-ampere current level

T. A. Shelkovenko, S. A. Pikuz, R. D. McBride, P. F. Knapp, H. Wilhelm, D. A. Hammer, and D. B. Sinars

Phys. Plasmas 16, 050702 (2009) (4 pages)

Online Publication Date: 12 May 2009

Full Text: PDF (273 kB)

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A symmetric X pinch configuration that is conducive to using large numbers of wires on >=1  MA pulsed power generators has been tested at 1 MA. Using an initial configuration of wires before their twisting, similar to nested cylindrical wire arrays, enables a geometrically simple, compact, multilayer wire configuration at the X pinch crossing region. Multilayer X pinches with the same or different materials in the inner and outer wire layers were tested. Optimization resulted in X pinch radiation sources with peak power comparable to the most successful single layer X pinch, but with a compact, single bright X radiation source more reliably obtained using the nested configuration.
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52.58.Lq, 52.59.Px

Static analysis of possible emittance growth of intense charged particle beams with thermal equilibrium distribution

Takashi Kikuchi and Kazuhiko Horioka

Phys. Plasmas 16, 050703 (2009) (4 pages)

Online Publication Date: 13 May 2009

Full Text: PDF (131 kB)

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Possible emittance growths of intense, nonuniform beams during a transport in a focusing channel are derived as a function of nonlinear field energy and space charge tune depression factors. The nonlinear field energy of the beam with thermal equilibrium distribution is estimated by considering the particle distribution across the cross section of the beam. The results show that the possible emittance growth can be suppressed by keeping the beam particle in thermal equilibrium distribution during the beam transport.
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52.59.Sa, 52.59.-f, 52.59.Fn, 52.58.Hm

Electron scale structures in collisionless magnetic reconnection

Neeraj Jain and A. Surjalal Sharma

Phys. Plasmas 16, 050704 (2009) (4 pages)

Online Publication Date: 19 May 2009

Full Text: PDF (509 kB)

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The early time-dependent phase of collisionless reconnection, which is dominated by electron dynamics, is investigated using electron-magnetohydrodynamic simulations. Simulations initialized with multi-wavelength perturbations lead to reconnection at multiple sites and the interaction of electron flows generated at the neighboring sites leads to secondary instabilities. These electron-scale processes limit the size of the current sheet and lead to an out-of-plane magnetic field with nested quadrupoles. These structures have important implications for multi-spacecraft missions exploring Earth's magnetotail.
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52.35.Vd, 52.65.Kj, 52.25.Fi, 52.30.Cv

A physical parametrization of coupled transverse dynamics based on generalized Courant–Snyder theory and its applications

Hong Qin and Ronald C. Davidson

Phys. Plasmas 16, 050705 (2009) (4 pages)

Online Publication Date: 26 May 2009

Full Text: PDF (90 kB)

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A physical parametrization of coupled transverse dynamics is developed by generalizing the Courant–Snyder (CS) theory for one degree of freedom to the case of coupled transverse dynamics with two degrees of freedom. The four basic components of the original CS theory, i.e., the envelope equation, phase advance, transfer matrix, and CS invariant, all have their counterparts with remarkably similar expressions in the generalized theory. Applications of the new theory are given. It is discovered that the stability of coupled dynamics is completely determined by the generalized phase advance.
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29.27.-a, 52.20.Dq
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ARTICLES

Basic Plasma Phenomena, Waves, Instabilities

Effect of ion and ion-beam mass ratio on the formation of ion-acoustic solitons in magnetized plasma in the presence of electron inertia

B. C. Kalita and S. N. Barman

Phys. Plasmas 16, 052101 (2009) (6 pages)

Online Publication Date: 4 May 2009

Full Text: PDF (130 kB)

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The propagation of ion-acoustic solitary waves in magnetized plasma with cold ions and ion-beams together with electron inertia has been investigated theoretically through the Korteweg–de Vries equation. Subject to the drift velocity of the ion beam, the existence of compressive solitons is found to become extinct as alpha (=cold ion mass/ion-beam mass) tends to 0.01 when gamma=0.985 (gamma is the beam velocity/phase velocity). Interestingly, a transitional direction of propagation of solitary waves has been unearthed for change over, from compressive solitons to rarefactive solitons based on alpha and sigmaupsilon(=cosine of the angle theta made by the wave propagation direction xi with the direction of the magnetic field) for fixed Q(=electron mass/ion mass). Further, the direction of propagation of ion-acoustic waves is found to be the deterministic factor to admit compressive or rarefactive solitons subject to beam outsource.
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52.35.Fp, 52.35.Sb

Self-excited surface plasmon-polaritons at the interface of counterstreaming plasmas

M. Lazar, W. M. Moslem, A. Smolyakov, and P. K. Shukla

Phys. Plasmas 16, 052102 (2009) (4 pages)

Online Publication Date: 7 May 2009

Full Text: PDF (115 kB)
See Also: Erratum

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Surface plasma modes are coupled electromagnetic/electrostatic (plasmon-polariton) excitations of free electrons near the vacuum-plasma or plasma-plasma interface. The surface plasmon-polariton propagates along the surface plane and decays on both sides of the boundary. The effect of counterstreaming on the surface plasmon-polariton excitation is examined. It is shown that the two-stream instability can excite self-consistently the surface modes at the interface of two counterstreaming plasmas. The dispersion relation is derived and the exact numerical solutions are plotted for comparison to the excitations of a nonstreaming plasma-plasma interface. Such plasma models are of interest in electronic signal transmission, as well as in astrophysical applications and in beam-plasma experiments.
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52.25.Os, 52.35.Fp, 52.35.Lv, 52.35.Qz

Investigation of spatiotemporal behavior of the plasma density during the development of the thermocurrent instability

M. M. Hatami, B. Shokri, A. R. Niknam, and A. Aliakbari

Phys. Plasmas 16, 052103 (2009) (4 pages)

Online Publication Date: 11 May 2009

Full Text: PDF (243 kB)

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Considering a weakly ionized, collisional, quasineutral plasma placed in an electric field under the condition of nonresonant Cerenkov radiation and using the hydrodynamic model, a nonlinear diffusionlike equation with negative diffusion coefficient is obtained, which describes the dynamics of plasma density during the development of the thermocurrent instability. This equation is solved by the Adomian decomposition method. According to this solution, the spatiotemporal behavior of the plasma density during the growth of the thermocurrent instability is investigated. It is shown that the development of the thermocurrent instability causes the initial perturbations in the plasma density to grow. Also, it is shown that the increment in these perturbations continues until the growth of the thermocurrent instability ceases due to the breakdown of the quasineutrality condition. In this case, it is seen that the profile of the plasma density does not change any more and gets to a constant limit.
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52.25.Fi, 52.35.Qz

On the electron whistler dispersion law in a cold plasma with light ions and heavy charged particulates

B. V. Lundin and C. Krafft

Phys. Plasmas 16, 052104 (2009) (11 pages)

Online Publication Date: 13 May 2009

Full Text: PDF (428 kB)

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The dispersion equation of electron whistler waves in a cold plasma with two light ions of comparable gyrofrequencies and heavy charged particulates is derived. It is valid in a very wide frequency range above the highest ion cutoff frequency when the wave frequency is essentially less than the electron plasma frequency. The derived electron whistler dispersion law is expressed through the relative contents of the two light ions and the electrons, as well as the characteristic frequencies of the magnetized plasma, as the lower hybrid resonance frequency, the two highest ion cutoff frequencies, the gyrofrequencies of the light ions, and the electron gyro- and plasma frequencies. The approximation of vanishingly small gyrofrequencies of the heavy ions permits to determine with a relevant accuracy the electron whistler dispersion law using the features of electron whistler spectrograms only. Estimates of the relative charge density of the light ions are obtained and the dispersion laws of the adjacent branches, i.e., the electron whistler waves and the so-called ion cyclotron whistlers are calculated. For the electron whistler waves, the presence of negative ions can be the origin of a manyfold increase in the lower cutoff frequency; a merging effect of the cutoff frequencies of the adjacent branches can also appear.
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52.27.Cm, 52.35.Hr, 52.50.Qt

Warm electromagnetic lower hybrid wave dispersion relation

A. L. Verdon, Iver H. Cairns, D. B. Melrose, and P. A. Robinson

Phys. Plasmas 16, 052105 (2009) (12 pages)

Online Publication Date: 13 May 2009

Full Text: PDF (938 kB)

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Lower hybrid (LH) waves can interact resonantly with both electrons and ions transferring energy between the species. For this reason the properties of LH waves are of interest. Most treatments of LH waves include either electromagnetic (EM) or warm plasma effects but not both. Here a new analytic dispersion relation for LH waves, including both EM and warm plasma effects, is derived and shown to be more consistent than the previous analytic dispersion relations with numerical results. These comparisons show a very good agreement of the real part of the frequency and reasonable agreement of the imaginary part for a wide range of parameters. It is found that ion magnetization effects, which have been neglected in all previous analytic treatments of LH waves, are surprisingly important. When ion magnetization effects become important the continuous LH mode breaks up into a series of segments of ion Bernstein modes.
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52.35.Hr

Hydromagnetic waves and instabilities in kappa distribution plasma

B. Basu

Phys. Plasmas 16, 052106 (2009) (11 pages)

Online Publication Date: 14 May 2009

Full Text: PDF (251 kB)

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Stability properties of hydromagnetic waves (shear and compressional Alfven waves) in spatially homogeneous plasma are investigated when the equilibrium particle velocity distributions in both parallel and perpendicular directions (in reference to the ambient magnetic field) are modeled by kappa distributions. Analysis is presented for the limiting cases |xialpha|<<1 and |xialpha|>>1 for which solutions of the dispersion relations are analytically tractable. Here xialpha(alpha=e,i) is the ratio of the wave phase speed and the electron (ion) thermal speed. Both low and high beta (=plasma pressure/magnetic pressure) plasmas are considered. The distinguishing features of the hydromagnetic waves in kappa distribution plasma are (1) both Landau damping and transit-time damping rates are larger than those in Maxwellian plasma because of the enhanced high-energy tail of the kappa distribution and (2) density and temperature perturbations in response to the electromagnetic perturbations are different from those in Maxwellian plasma when |xialpha|<<1. Moreover, frequency of the oscillatory stable modes (e.g., kinetic shear Alfven wave) and excitation condition of the nonoscillatory (zero frequency) unstable modes (e.g., mirror instability) in kappa distribution plasma are also different from those in Maxwellian plasma. Quantitative estimates of the differences depend on the specific choice of the kappa distribution. For simplicity of notations, same spectral indices kappa|| and kappa[perpendicular] have been assumed for both electron and ion population. However, the analysis can be easily generalized to allow for different values of the spectral indices for the two charged populations.
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52.35.Bj, 52.35.Qz

Magnetic reconnection with pressure tensor in electron magnetohydrodynamics

Huishan Cai and Ding Li

Phys. Plasmas 16, 052107 (2009) (5 pages)

Online Publication Date: 15 May 2009

Full Text: PDF (146 kB)

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The dissipation mechanisms of reconnection and the pressure gradient effects on tearing mode with guide magnetic field are analyzed systematically by including the electron pressure tensor in electron magnetohydrodynamics. It is found that which dissipation mechanism dominates, either pressure-based dissipation or inertia-based dissipation, has a great relation with the relative scaling orders between the electron thermal Larmor radius and electron inertia skin depth. The effects of pressure gradient also depend on the relative magnitude between parallel and perpendicular equilibrium pressure gradients. When the pressure-based dissipation is dominant, the condition that pressure drives or suppresses tearing mode instability also depends on the relative magnitude between parallel and perpendicular equilibrium pressure gradients.
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52.35.Vd, 52.30.Cv, 52.25.Fi, 52.35.Py

Filamentation of laser in a magnetized plasma under relativistic and ponderomotive nonlinearities

Ranjeet Singh and V. K. Tripathi

Phys. Plasmas 16, 052108 (2009) (5 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (153 kB)

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Filamentation of a circularly polarized short pulse laser propagating along the direction of ambient magnetic field in plasma is studied. The nonlinearity arises through the combined effect of relativistic mass variation and ponderomotive force induced electron cavitation. The growth rate is maximum Gammamax for an optimum filament size, q<sub>opt</sub><sup>-1</sup>. Gammamax and qopt increases with plasma density and ambient magnetic field.
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52.38.-r, 52.35.Mw, 52.27.Ny

Linear coupling of Alfven waves and acoustic-type modes in dense quantum magnetoplasmas

S. A. Khan and H. Saleem

Phys. Plasmas 16, 052109 (2009) (6 pages)

Online Publication Date: 27 May 2009

Full Text: PDF (289 kB)

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A coupled dispersion relation of low frequency shear Alfven waves and electrostatic waves in a dense quantum magnetoplasma is derived by using hydrodynamic model. The dispersive contribution of electron quantum effects is discussed for dynamic as well as static ions. The dominant role of electron Fermi pressure is highlighted and its comparison with the quantum pressure arising due to quantum Bohm potential is presented. For illustrative purpose, the results are analyzed numerically. The relevance of present work with the dense astrophysical and laboratory plasmas is pointed out with possible consequences.
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52.35.Bj, 52.35.Py, 52.30.Cv

Tests of collision operators using laboratory measurements of shear Alfvén wave dispersion and damping

D. J. Thuecks, C. A. Kletzing, F. Skiff, S. R. Bounds, and S. Vincena

Phys. Plasmas 16, 052110 (2009) (11 pages)

Online Publication Date: 28 May 2009

Full Text: PDF (621 kB)

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Measurements of shear Alfvén waves are used to test the predictions of a variety of different electron collision operators, including several Krook collision operators as well as a Lorentz collision operator. New expressions for the collisional warm-plasma dielectric tensor resulting from the use of the fully magnetized collisional Boltzmann equation are presented here. Theoretical predictions for the parallel phase velocity and damping as a function of perpendicular wave number k[perpendicular] are derived from the dielectric tensor. Laboratory measurements of the parallel phase velocity and damping of shear Alfvén waves were made to test these theoretical predictions in both the kinetic (vte>>vA) and inertial (vte<<vA) parameter regimes and at several wave frequencies (omega<omegaci). Results show that, in the inertial regime, the best match between measurements and theory occur when any of the Krook operators are used to describe electron collisions. In contrast, the best agreement in the kinetic regime is found when collisions are completely ignored.
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52.35.Hr, 52.20.Fs, 52.72.+v

Parker problem in Hall magnetohydrodynamics

Bhimsen K. Shivamoggi

Phys. Plasmas 16, 052111 (2009) (4 pages)

Online Publication Date: 28 May 2009

Full Text: PDF (89 kB)

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The Parker problem in Hall magnetohydrodynamics (MHD) is considered. Poloidal shear superposed on the toroidal ion flow associated with the Hall effect is incorporated. This is found to lead to a triple deck structure for the Parker problem in Hall MHD, with the magnetic field falling off in the intermediate Hall-resistive region more steeply (like 1/x3) than that (like 1/x) in the outer ideal MHD region.
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52.30.Cv, 52.55.Tn

Nonlinear Phenomena, Turbulence, Transport

Implementation and application of two synthetic diagnostics for validating simulations of core tokamak turbulence

C. Holland, A. E. White, G. R. McKee, M. W. Shafer, J. Candy, R. E. Waltz, L. Schmitz, and G. R. Tynan

Phys. Plasmas 16, 052301 (2009) (15 pages)

Online Publication Date: 1 May 2009

Full Text: PDF (555 kB)

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The deployment of multiple high-resolution, spatially localized fluctuation diagnostics on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] opens the door to a new level of core turbulence model validation. Toward this end, the implementation of synthetic diagnostics that model physical beam emission spectroscopy and correlation electron cyclotron emission diagnostics is presented. Initial results from their applications to local gyrokinetic simulations of two locations in a DIII-D L-mode discharge performed with the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] are also discussed. At normalized toroidal flux rho=0.5, we find very good agreement between experiment and simulation in both the energy flows and fluctuation levels measured by both diagnostics. However, at rho=0.75, GYRO underpredicts the observed energy flows by roughly a factor of 7, with rms fluctuation levels underpredicted by a factor of 3. Interestingly, at both locations we find good agreement in the shapes of the radial and vertical density correlation functions and in the shapes of the frequency power spectra. At both locations, the attenuation of the GYRO-predicted fluctuations due to the spatial averaging imposed by the diagnostics' spot sizes is significant, and its incorporation via the use of synthetic diagnostics is shown to be essential for quantitative comparisons such as these.
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52.35.Ra, 52.25.Fi, 52.30.Gz, 52.55.Fa, 52.65.Tt

A novel mechanism for exciting intrinsic toroidal rotation

C. J. McDevitt, P. H. Diamond, Ö. D. Gürcan, and T. S. Hahm

Phys. Plasmas 16, 052302 (2009) (12 pages)

Online Publication Date: 4 May 2009

Full Text: PDF (222 kB)

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Beginning from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers two physically distinct mechanisms by which microturbulence may drive intrinsic rotation. The first mechanism, which emanates from E×B convection of parallel momentum, has already been analyzed [O. D. Gurcan et al., Phys. Plasmas 14, 042306 (2007); R. R. Dominguez and G. M. Staebler, Phys. Fluids B 5, 3876 (1993)] and was shown to follow from radial electric field shear induced symmetry breaking of the spectrally averaged parallel wave number. Thus, this mechanism is most likely active in regions with steep pressure gradients or strong poloidal flow shear. The second mechanism uncovered, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. This novel means of driving intrinsic rotation, while nominally higher order in an expansion of the mode frequency divided by the ion cyclotron frequency, does not depend on radial electric field shear. Thus, while the magnitude of the former mechanism is strongly reduced in regions of weak radial electric field shear, this mechanism remains unabated and is thus likely relevant in complementary regimes.
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52.30.-q, 52.35.Ra, 52.55.Hc

Finite orbit width effect in ion collisional transport in TJ-II

J. L. Velasco, F. Castejón, and A. Tarancón

Phys. Plasmas 16, 052303 (2009) (9 pages)

Online Publication Date: 7 May 2009

Full Text: PDF (282 kB)

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The validity of the traditional local diffusive approach and of the use of monoenergetic calculations has been studied for the stellarator TJ-II [Alejaldre et al., Fusion Technol. 17, 131 (1990)]: it is shown to be doubtful, under some circumstances, even in a purely collisional description of transport. The diffusion in physical space starting from Dirac-delta-like initial conditions has been studied using the code Integrator of Stochastic Differential Equations for Plasmas by Castejón et al. [Plasma Phys. Controlled Fusion 49, 753 (2007)]. Particles may experience large radial excursions from their original magnetic surfaces in a single collisional time. The contribution of these particles to the flux may make it nondiffusive; non-Gaussian density distributions, characterized by long tails, are observed. In the velocity space, there are important variations in the average particle kinetic energy after one collision time. We discuss the effect of this fact over the calculation of monoenergetic transport coefficients and their convolution. A simple analysis based on Hurst exponents has shown nevertheless that the description of transport by means of a pinch term and an effective transport coefficient is more correct than expected.
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52.25.Fi, 52.20.-j, 52.55.Hc

Probability distribution function for self-organization of shear flows

Eun-jin Kim, Han-Li Liu, and Johan Anderson

Phys. Plasmas 16, 052304 (2009) (5 pages)

Online Publication Date: 14 May 2009

Full Text: PDF (145 kB)

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The first prediction of the probability distribution function (PDF) of self-organized shear flows is presented in a nonlinear diffusion model where shear flows are generated by a stochastic forcing while diffused by a nonlinear eddy diffusivity. A novel nonperturbative method based on a coherent structure is utilized for the prediction of the strongly intermittent exponential PDF tails of the gradient of shear flows. Numerical simulations using Gaussian forcing not only confirm these predictions but also reveal the significant contribution from the PDF tails with a large population of supercritical gradients. The validity of the nonlinear diffusion model is then examined using a threshold model where eddy diffusivity is given by discontinuous values, elucidating an important role of relative time scales of relaxation and disturbance in the determination of the PDFs.
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52.30.-q, 52.35.Mw, 52.25.Fi, 52.65.Ff, 02.50.Ey, 02.60.Cb

Particle-in-cell simulation with Vlasov ions and drift kinetic electrons

Yang Chen and Scott E. Parker

Phys. Plasmas 16, 052305 (2009) (9 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (407 kB)

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There are certain limitations in using gyrokinetic ions for simulations of turbulent transport in tokamak plasmas. Applications where Vlasov ions might be more appropriate include the electron temperature gradient driven turbulence, edge turbulence with steep density gradient, and magnetic reconnection in a weak guide field. In such cases the ion gyrokinetic model presently used in simulations needs to be extended, but a satisfactory extension valid for fully electromagnetic turbulence is not presently available. Even if an accurate model is found, its numerical implementation could be very challenging. We propose a kinetic model that combines Vlasov ions with gyrokinetic electrons to avoid the difficulties with gyrokinetic ions. The field equations of this model are the Faraday's equation and the Ampere's equation without the displacement current. The perturbed fields B1 and E1 rather than the scalar and vector potentials are used to formulate the field equations. We have devised an implicit scheme for this model, demonstrated in three-dimensional slab for the Alfvén waves, the drift Alfvén instability and the ion acoustic waves.
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52.65.-y, 52.35.Bj, 52.35.Kt, 52.35.Qz, 52.35.Ra, 52.55.Fa

Equal energy phase space trajectories in resonant wave interactions

O. Yaakobi and L. Friedland

Phys. Plasmas 16, 052306 (2009) (7 pages)

Online Publication Date: 26 May 2009

Full Text: PDF (3545 kB)

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Adiabatic evolution of two and three resonantly interacting wave systems with nonlinear frequency/wave vector shifts is discussed. The corresponding Hamiltonian, depending on the coupling, detuning, and nonlinear frequency shift parameters may have a variable number of fixed points, i.e., the system can experience a topological change of phase space when these parameters vary in time or space. It is shown that the oscillation periods of two equal energy trajectories in these wave systems are equal and the difference between the action integrals of such trajectories is obtained analytically as a function of the system parameters. Based on these findings, a scheme of simultaneous adiabatic variation in the parameters is designed, such that any pair of initially equal energy trajectories continues to have the same energy at later times. These results are generalizations of a previous work [O. Polomarov and G. Shvets, Phys. Plasmas 13, 054502 (2006)] for a single, resonantly driven wave.
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52.35.Mw

Quasisteady and steady states in global gyrokinetic particle-in-cell simulations

S. Jolliet, B. F. McMillan, T. Vernay, L. Villard, A. Bottino, and P. Angelino

Phys. Plasmas 16, 052307 (2009) (10 pages)

Online Publication Date: 26 May 2009

Full Text: PDF (954 kB)

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Collisionless delta-f gyrokinetic particle-in-cell simulations suffer from the entropy paradox, in which the entropy grows linearly in time while low-order moments are saturated. As a consequence, these simulations do not reach a steady state and are unsuited to make quantitative predictions. A solution to this issue is the introduction of artificial dissipation. The notion of steady state in gyrokinetic simulations is studied by deriving an evolution equation for the fluctuation entropy and applying it to the global collisionless particle-in-cell code ORB5 [S. Jolliet et al., Comput. Phys. Commun. 177, 409 (2007)]. It is shown that a recently implemented noise-control algorithm [B. F. McMillan et al., Phys. Plasmas 15, 052308 (2008)] based on a W-stat provides the necessary dissipation to reach a steady state. The two interesting situations of decaying and driven turbulence are considered. In addition, it is shown that a separate heating algorithm, not based on a W-stat, does not lead to a statistical steady state.
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52.65.-y, 52.35.Ra

Non-Markovian renormalization of kinetic coefficients for drift-type turbulence in magnetized plasmas

A. Zagorodny and J. Weiland

Phys. Plasmas 16, 052308 (2009) (9 pages)

Online Publication Date: 27 May 2009

Full Text: PDF (159 kB)

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The problem of derivation of the kinetic equations for inhomogeneous plasma in an external magnetic field is considered. The Fokker–Planck-type equations with the non-Markovian kinetic coefficients are proposed. In the time-local limit (small correlation times with respect to the distribution function relaxation time) the relations obtained recover the results known from the appropriate quasilinear theory and the Dupree–Weinstock theory of plasma turbulence. Kinetic calculations of the dielectric response function are also performed with regard to the influence of turbulent fields on particle motion. The equations proposed are used to describe zonal flow generation and to estimate the diffusion coefficient for saturated turbulence.
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52.35.Ra, 52.25.Dg, 52.30.-q, 52.25.Mq, 52.55.-s

Effects of positron density and temperature on ion-acoustic solitary waves in a magnetized electron-positron-ion plasma: Oblique propagation

A. Esfandyari-Kalejahi, M. Mehdipoor, and M. Akbari-Moghanjoughi

Phys. Plasmas 16, 052309 (2009) (6 pages)

Online Publication Date: 28 May 2009

Full Text: PDF (174 kB)

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Ion-acoustic (IA) solitary waves are investigated in a magnetized three-component plasma consisting of cold ions, isothermal hot electrons, and positrons. The basic set of fluid equations is reduced to the Korteweg de Vries equation using the standard reductive perturbation (multiple-scale) technique. Theoretical and numerical analyses confirm significant effects of the presence of positrons and the dependence of the electron to positron temperature ratio on the amplitude and the width of IA solitary waves. It is shown that the rarefactive and compressive IA solitary excitations can propagate when the propagation angle theta satisfies 0<=theta<pi/2 and pi/2<theta<=pi, respectively. Also, it is remarked that the amplitude of the rarefactive and compressive IA solitary excitations is not affected by the magnitude of external magnetic field B0, whereas their width depends strictly on B0. The numerical analysis has been done based on the typical numerical data from a pulsar magnetosphere.
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52.25.Xz, 52.27.Ep, 52.35.Fp, 52.35.Mw

Magnetically Confined Plasmas, Heating, Confinement

Moment approach to the bootstrap current in nonaxisymmetric toroidal plasmas using deltaf Monte Carlo methods

A. Matsuyama, M. Yu. Isaev, K. Y. Watanabe, K. Hanatani, Y. Suzuki, N. Nakajima, W. A. Cooper, and T. M. Tran

Phys. Plasmas 16, 052501 (2009) (9 pages)

Online Publication Date: 7 May 2009

Full Text: PDF (262 kB)

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To evaluate the bootstrap current in nonaxisymmetric toroidal plasmas quantitatively, a deltaf Monte Carlo method is incorporated into the moment approach. From the drift-kinetic equation with the pitch-angle scattering collision operator, the bootstrap current and neoclassical conductivity coefficients are calculated. The neoclassical viscosity is evaluated from these two monoenergetic transport coefficients. Numerical results obtained by the deltaf Monte Carlo method for a model heliotron are in reasonable agreement with asymptotic formulae and with the results obtained by the variational principle.
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52.25.Fi, 52.55.Hc, 52.25.Dg, 52.20.Fs, 52.20.Hv, 52.65.Pp

Effect of local E×B flow shear on the stability of magnetic islands in tokamak plasmas

R. Fitzpatrick and F. L. Waelbroeck

Phys. Plasmas 16, 052502 (2009) (9 pages)

Online Publication Date: 8 May 2009

Full Text: PDF (299 kB)

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The influence of local E×B flow shear on a relatively wide, constant-psi, magnetic island embedded in a large-aspect-ratio, low-beta, circular cross-section tokamak plasma is examined, using a slab approximation to model the magnetic geometry. It is found that there are three separate solution branches characterized by low, intermediate, and high values of the shear. Flow shear is found to have a stabilizing effect on island solutions lying on the low and high shear branches, via a nonlinear modification of the ion polarization term in the Rutherford island width evolution equation, but to have a destabilizing effect on solutions lying on the intermediate shear branch. Moreover, the effect is independent of the sign of the shear. The modification of island stability by local E×B flow shear is found to peak when the magnitude of the shear is approximately vi/Ls, where vi is the ion thermal velocity, and Ls the magnetic shear length.
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52.55.Fa, 52.30.Cv, 52.35.Py

Resistive ferromagnetic wall modes in theory and experiment

V. D. Pustovitov

Phys. Plasmas 16, 052503 (2009) (10 pages)

Online Publication Date: 8 May 2009

Full Text: PDF (214 kB)

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Effects of the ferromagnetic resistive wall on the plasma stability are analyzed. The analysis is based on the equations describing the perturbation dynamics outside the plasma, assuming a linear plasma response. A single-mode cylindrical model is used with two features that differ from the standard case: the wall magnetic permeability is incorporated and the thin-wall approximation is waived. The derivations are performed so that the results can be applied to both tokamaks and line-tied pinches. This is done to allow conclusions for tokamaks from comparison of the developed theory with the experimental data on the resistive and ferromagnetic wall modes in the Wisconsin rotating wall machine with and without a ferritic wall [W. F. Bergerson, D. A. Hannum, C. C. Hegna, R. D. Kendrick, J. S. Sarff, and C. B. Forest, Phys. Rev. Lett. 101, 235005 (2008)]. The model shows that the ferromagnetic wall effect is always destabilizing. However, it must be small under standard conditions in tokamaks. The effect can be much stronger in the pinch with lower magnetic field and larger wall permeability. The dispersion relation obtained here makes possible an explanation of the experimental results available so far, including those from the Wisconsin machine reported recently as strongly contradictory to expectations based on earlier models. Also, an easy practical solution for compensating the destabilizing ferromagnetic effect in tokamaks is proposed.
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52.35.Py, 52.40.Hf, 52.55.Fa

Exact solutions for axisymmetric nonlinear magnetohydrodynamic equilibria of aligned magnetic field and plasma flow with applications to astrophysics and plasma confinement devices

A. H. Khater and S. M. Moawad

Phys. Plasmas 16, 052504 (2009) (7 pages)

Online Publication Date: 8 May 2009

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The steady state equations of magnetohydrodynamic (MHD) flows for an inviscid fluid of high electrical conductivity are considered for an axisymmetric case, in which the physical quantities are independent of the coordinate phi of a cylindrical coordinate system (r,phi,z). The magnetic field is taken to be aligned to the plasma velocity, i.e., the magnetic lines of force and the streamlines of the velocity field coincide. Two classes of exact solutions are obtained. The obtained solutions are smooth everywhere and satisfy all necessary physical conditions, in which they have applications in astrophysics as well as plasma confinement devices, e.g., tokamak and reversed field pinch.
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52.30.Cv, 52.25.Fi, 52.55.Fa, 52.58.Lq, 52.55.Ez

Plasma torque and nonambipolar transport

Allen H. Boozer

Phys. Plasmas 16, 052505 (2009) (15 pages)

Online Publication Date: 14 May 2009

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Poloidal symmetry breaking in toroidal plasmas causes a damping of poloidal rotation and toroidal symmetry breaking a damping of toroidal rotation. These torques are transmitted by the magnetic field to the outside world. An upper limit exists on the torque that can be transmitted by magnetic asymmetries. This limit is enforced by shielding asymmetries from the plasma, which can be an important effect for toroidal asymmetries. The torque interaction of plasmas with magnetic fields can be either through an anisotropic pressure or by the drive for magnetic islands. The physics of both types of interactions are considered and paradoxical effects are clarified.
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52.55.Hc, 52.30.-q, 52.25.Fi

Aspect-ratio effects in the driven, flux-core spheromak

E. B. Hooper, C. A. Romero-Talamás, L. L. LoDestro, R. D. Wood, and H. S. McLean

Phys. Plasmas 16, 052506 (2009) (9 pages) Multimedia

Online Publication Date: 19 May 2009

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Resistive magnetohydrodynamic simulations are used to evaluate the effects of the aspect ratio A (length to radius ratio) in a spheromak driven by coaxial helicity injection. The simulations are benchmarked against the Sustained Spheromak Physics Experiment (SSPX) [R. D. Wood et al., Nucl. Fusion 45, 1582 (2005)]. Amplification of the bias (“gun”) poloidal flux is fitted well by a linear dependence (insensitive to A) on the ratio of gun current and bias flux above a threshold dependent on A. For low flux amplifications in the simulations, the n=1 mode is coherent and the mean-field geometry looks like a tilted spheromak. Because the mode has relatively large amplitude the field lines are open everywhere, allowing helicity penetration. Strongly driven helicity injection at A<=1.4 in simulations generates reconnection events which generate cathode-voltage spikes, relaxation of the symmetry-breaking modes, and open, stochastic magnetic field lines; this state is characteristic of SSPX. The time sequences of these events suggest that they are representative of a chaotic process. Near the spheromak tilt-mode limit, A[approximate]1.67 for a cylindrical flux conserver, the tilt approaches 90°; reconnection events are not generated up to the strongest drives simulated. Implications for spheromak experiments are discussed.
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52.55.Ip, 52.65.Kj

A comprehensive gyrokinetic description of global electrostatic microinstabilities in a tokamak

J. Chowdhury, R. Ganesh, S. Brunner, J. Vaclavik, L. Villard, and P. Angelino

Phys. Plasmas 16, 052507 (2009) (9 pages)

Online Publication Date: 20 May 2009

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It is believed that low frequency microinstabilities such as ion temperature gradient (ITG) driven modes and trapped electron modes (TEMs) are largely responsible for the experimentally observed anomalous transport via the ion and electron channels in a tokamak. In the present work, a comprehensive global linear gyrokinetic model incorporating fully kinetic (trapped and passing) electrons and ions, actual ion to electron mass ratio, radial coupling, and profile variation is used to investigate the ITG driven modes and pure TEMs. These modes are found to exhibit multiscale structures in the presence of nonadiabatic passing electrons. The multiscale structure is related to the large nonadiabaticity of electrons in the vicinity of mode rational magnetic surfaces and leads to reduced mixing length estimates of transport compared to those obtained from adiabatic electron models.
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52.35.Qz, 52.25.Fi, 52.55.Fa, 52.25.Dg, 52.30.Gz

Effects of compressibility and heating in magnetohydrodynamics simulations of a reversed field pinch

M. Onofri, F. Malara, and P. Veltri

Phys. Plasmas 16, 052508 (2009) (9 pages)

Online Publication Date: 22 May 2009

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The reversed field pinch is studied using numerical simulations of the compressible magnetohydrodynamics equations. Contrary to what has been done in previous works, the hypotheses of constant density and vanishing pressure are not used. Two cases are investigated. In the first case the pressure is derived from an adiabatic condition and in the second case the pressure equation includes heating terms due to resistivity and viscosity. The evolution of the reversal parameter and the production of single helicity or multiple helicity states are different in the two cases. The simulations show that the results are affected by compressibility and are very sensitive to hypotheses on heat production.
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52.55.Ez, 52.30.Cv, 52.25.Kn, 52.25.Fi, 52.65.Kj

A paradigm shift from stationary stability to dynamically evolving stability required from experimental fusion plasmas

Yoshiomi Kondoh

Phys. Plasmas 16, 052509 (2009) (14 pages)

Online Publication Date: 26 May 2009

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A paradigm shift from the traditional concept of stationary stability to the new one of dynamically evolving stability is proposed in order to correctly deal with dynamically evolving experimental plasmas. A new process to derive generalized simultaneous eigenvalue equations is presented by the use of a generalized theory of self-organization. The final simultaneous eigenvalue equations are shown to be a good candidate for the proposed paradigm shift because their mathematical forms exactly describe the self-similarly evolving and dynamically stable states available to various dynamic systems. Typical numerical configurations of mutually dependent, dynamically stable, and self-similarly evolving physical quantities are presented for the reversed-field pinch plasmas in cylindrical geometry by solving a set of simultaneous eigenvalue equations for the two-fluid model. A new algorithm is presented to find the dynamically stable, self-similarly evolving and self-organized configurations and to investigate quantitatively the robust dynamical stability of these configurations.
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52.35.Qz, 52.58.Lq

Driving toroidally asymmetric current through the tokamak scrape-off layer. I. Potential for edge localized mode suppression

Ilon Joseph, Ronald H. Cohen, and Dmitri D. Ryutov

Phys. Plasmas 16, 052510 (2009) (14 pages)

Online Publication Date: 26 May 2009

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A potential technique for suppressing edge localized modes is theoretically analyzed. Recent experiments have shown that externally generated resonant magnetic perturbations (RMPs) can stabilize edge localized modes (ELMs) by modifying the density profile [T. E. Evans et al., Nat. Phys. 2, 419 (2006); Y. Liang et al., Phys. Rev. Lett. 98, 265004 (2007)]. Driving toroidally asymmetric current internally through the scrape-off layer (SOL) plasma itself can also generate RMPs that are close to the required threshold for ELM control. Ion saturation current densities can be achieved by producing potential differences on the order of the electron temperature. Although the threshold is uncertain in future devices, if driven coherently through the SOL, the upper limit for the resulting perturbation field would exceed the present experimental threshold. This analysis provides the tools required for estimating the magnitude of the coherent SOL current and RMP generated via toroidally asymmetric biasing of the target. Flux expansion increases the perturbation near the X-point, while phase interference due to the shearing of field lines near the X-point reduces the amplitude of the effective SOL perturbation and makes the result sensitive to both toroidal mode number n and the phasing at the target plate. If the current density driven at the target plate decays radially, the amplitude over the useful coherence width of the current profile will be reduced. The RMP can still exceed the present threshold at low n if the radial location and width of the biasing region are optimally chosen.
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52.25.Fi, 52.30.Cv, 52.35.Py, 52.40.Hf, 52.55.Fa, 52.65.-y

Driving toroidally asymmetric current through the tokamak scrape-off layer. II. Magnetic field structure and spectrum

Ilon Joseph

Phys. Plasmas 16, 052511 (2009) (15 pages)

Online Publication Date: 26 May 2009

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The structure of the magnetic field perturbations due to nonaxisymmetric field-aligned currents in the tokamak scrape-off layer (SOL) are analytically calculated near the X-point. Paper I [I. Joseph et al., Phys. Plasmas 16, 052510 (2009)] demonstrated that biasing divertor target plates in a toroidally asymmetric fashion can generate an appreciable toroidally asymmetric parallel current density in the SOL along the separatrix. Here, the magnetic field perturbation caused by a SOL current channel of finite width and stepwise constant amplitude at the target plate is derived. Flux expansion amplifies the magnetic perturbation near the X-point, while phase interference causes the SOL amplitude to be reduced at large toroidal mode number. Far enough from the current channel, the magnetic field can be approximated as arising from a surface current near the separatrix with differing amplitudes in the SOL and the divertor leg. The perturbation spectrum and resonant components of this field are computed analytically asymptotically close to the separatrix in magnetic flux coordinates. The size of the stochastic layer due to the applied perturbation that would result without self-consistent plasma shielding is also estimated. If enough resonant field is generated, control of the edge pressure gradient may allow stabilization of edge localized modes.
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52.25.Fi, 52.30.Cv, 52.35.Py, 52.40.Hf, 52.55.Rk, 52.55.Fa

Nonlinear cyclotron harmonic absorption

JaeChun Seol, C. C. Hegna, and J. D. Callen

Phys. Plasmas 16, 052512 (2009) (5 pages)

Online Publication Date: 27 May 2009

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Nonlinear oscillations of particle's energy occur when a particle stays in a resonance zone. In this work, we found that collisionless heating of particles occurs when they pass the microwave beam at first, second, and third harmonic resonances. It is found that the net energy gain of particles from the microwaves is inversely proportional to the wave frequency. It is also found that the net energy gain is dependent on the microwave beam width. The energy gain of particles from a single pass through a resonance zone has been formulated analytically. A numerical calculation has been performed and the results are in good agreement with the analytic calculation. Both analytic and numerical calculations show a strong frequency dependence and a beam width dependence of nonlinear cyclotron resonance heating.
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52.50.Sw, 52.40.Db, 52.35.Mw

Comparison of the Monte Carlo ion cyclotron heating model with the full-wave linear absorption model

M. Choi, V. S. Chan, L. A. Berry, E. F. Jaeger, D. Green, P. Bonoli, J. Wright, and RF SciDAC Team

Phys. Plasmas 16, 052513 (2009) (8 pages)

Online Publication Date: 28 May 2009

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To fully account for the wave-particle interaction physics in ion cyclotron resonant frequency (ICRF) heating experiment, finite orbit effects and non-Maxwellian distribution have to be self-consistently coupled with full-wave solutions. For this purpose, the five-dimensional Monte Carlo code ORBIT-RF [M. Choi et al., Phys. Plasmas 12, 1 (2005)] is being coupled with the two-dimensional full-wave code AORSA [E. F. Jaeger et al., Phys. Plasmas 13, 056101 (2006)] to iteratively evolve the ion distribution in four-dimensional spatial velocity space that is used to update the dielectric tensor in AORSA for evaluating the full-wave fields. In this paper, it is demonstrated that using the full-wave fields from a Maxwellian dielectric tensor in AORSA and confining the resonant ions to their initial orbits in ORBIT-RF, ORBIT-RF largely reproduces the AORSA linear wave absorption profiles for fundamental and higher harmonic ICRF heating. An exception is an observed inward shift in the ORBIT-RF absorption peak for high harmonics near the magnetic axis compared with that of AORSA, which can be attributed to a finite orbit width effect. The success of this verification supports the validity of the Monte Carlo wave-particle interaction model and the readiness of the iterative coupling between ORBIT-RF and AORSA for an improved modeling of ICRF heating experiments.
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52.50.Gj, 52.50.Qt, 52.65.Pp

Nonlocal analysis of the excitation of the geodesic acoustic mode by drift waves

P. N. Guzdar, R. G. Kleva, N. Chakrabarti, V. Naulin, J. J. Rasmussen, P. K. Kaw, and R. Singh

Phys. Plasmas 16, 052514 (2009) (7 pages)

Online Publication Date: 28 May 2009

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The geodesic acoustic modes (GAMs) are typically observed in the edge region of toroidal plasmas. Drift waves have been identified as a possible cause of excitation of GAMs by a resonant three wave parametric process. A nonlocal theory of excitation of these modes in inhomogeneous plasmas typical of the edge region of tokamaks is presented in this paper. The continuum GAM modes with coupling to the drift waves can create discrete “global” unstable eigenmodes localized in the edge “pedestal” region of the plasma. Multiple resonantly driven unstable radial eigenmodes can coexist on the edge pedestal.
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52.35.Mw, 52.35.Kt, 52.55.Fa

Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

Two-plasmon-decay instability in direct-drive inertial confinement fusion experiments

W. Seka, D. H. Edgell, J. F. Myatt, A. V. Maximov, R. W. Short, V. N. Goncharov, and H. A. Baldis

Phys. Plasmas 16, 052701 (2009) (7 pages)

Online Publication Date: 8 May 2009

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The two-plasmon-decay (TPD) instability in direct-drive irradiation OMEGA [J. M. Soures, R. L. McCrory, C. P. Verdon, et al., Phys. Plasmas 3, 2108 (1996)] experiments is seen in the half-integer harmonic emission. Experimental time-resolved omega/2 and 3omega/2 spectra indicate that the linear theory for the absolute TPD instability reasonably predicts TPD thresholds. The plasma wave spectra do not, however, agree at all with the predictions of the linear theory. This is most likely a consequence of the nonlinear evolution of this instability once it is above threshold. This is demonstrated with spectral data obtained from spherical implosion experiments as well as planar target experiments. In the latter, Thomson scattering shows the importance of the Landau cutoff. For the TPD instability, the Landau cutoff is found to be respected in all spherical and planar target experiments. In addition, the maximum plasma wave amplitudes appear to occur near the Landau cutoff.
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52.35.Qz, 52.35.Mw, 52.35.Fp, 52.38.Bv, 52.25.Os, 52.57.-z

Al 1s-2p absorption spectroscopy of shock-wave heating and compression in laser-driven planar foil

H. Sawada, S. P. Regan, P. B. Radha, R. Epstein, D. Li, V. N. Goncharov, S. X. Hu, D. D. Meyerhofer, J. A. Delettrez, P. A. Jaanimagi, V. A. Smalyuk, T. R. Boehly, T. C. Sangster, B. Yaakobi, and R. C. Mancini

Phys. Plasmas 16, 052702 (2009) (14 pages)

Online Publication Date: 15 May 2009

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Time-resolved Al 1s-2p absorption spectroscopy is used to diagnose direct-drive, shock-wave heating and compression of planar targets having nearly Fermi-degenerate plasma conditions (Te~10–40  eV, rho~3–11  g/cm3) on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. A planar plastic foil with a buried Al tracer layer was irradiated with peak intensities of 1014–1015  W/cm2 and probed with the pseudocontinuum M-band emission from a point-source Sm backlighter in the range of 1.4–1.7 keV. The laser ablation process launches 10–70 Mbar shock waves into the CH/Al/CH target. The Al 1s-2p absorption spectra were analyzed using the atomic physic code PRISMSPECT to infer Te and rho in the Al layer, assuming uniform plasma conditions during shock-wave heating, and to determine when the heat front penetrated the Al layer. The drive foils were simulated with the one-dimensional hydrodynamics code LILAC using a flux-limited (f=0.06 and f=0.1) and nonlocal thermal-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)]. The predictions of simulated shock-wave heating and the timing of heat-front penetration are compared to the observations. The experimental results for a wide variety of laser-drive conditions and buried depths have shown that the LILAC predictions using f=0.06 and the nonlocal model accurately model the shock-wave heating and timing of the heat-front penetration while the shock is transiting the target. The observed discrepancy between the measured and simulated shock-wave heating at late times of the drive can be explained by the reduced radiative heating due to lateral heat flow in the corona.
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52.70.Kz, 52.50.Lp, 52.35.Tc, 52.50.Jm, 52.38.Mf, 52.25.Fi

Absolute x-ray yields from laser-irradiated germanium-doped low-density aerogels

K. B. Fournier, J. H. Satcher, M. J. May, J. F. Poco, C. M. Sorce, J. D. Colvin, S. B. Hansen, S. A. MacLaren, S. J. Moon, J. F. Davis, F. Girard, B. Villette, M. Primout, D. Babonneau, C. A. Coverdale et al.

Phys. Plasmas 16, 052703 (2009) (13 pages)

Online Publication Date: 19 May 2009

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The x-ray yields from laser-irradiated germanium-doped ultra-low-density aerogel plasmas have been measured in the energy range from sub-keV to [approximate]15 keV at the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The targets' x-ray yields have been studied for variation in target size, aerogel density, laser pulse length, and laser intensity. For targets that result in plasmas with electron densities in the range of [approximate]10% of the critical density for 3omega light, one can expect 10–11 J/sr of x rays with energies above 9 keV, and 600–800 J/sr for energies below 3.5 keV. In addition to the x-ray spectral yields, the x-ray temporal waveforms have been measured and it is observed that the emitted x rays generally follow the delivered laser power, with late-time enhancements of emitted x-ray power correlated with hydrodynamic compression of the hot plasma. Further, the laser energy reflected from the target by plasma instabilities is found to be 2%–7% of the incident energy for individual beam intensities [approximate]1014–1015  W/cm2. The propagation of the laser heating in the target volume has been characterized with two-dimensional imaging. Source-region heating is seen to be correlated with the temporal profile of the emitted x-ray power.
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52.50.Jm, 52.59.Px, 52.35.Py, 52.25.Os

Titanium and germanium lined hohlraums and halfraums as multi-keV x-ray radiators

F. Girard, M. Primout, B. Villette, Ph. Stemmler, L. Jacquet, D. Babonneau, and K. B. Fournier

Phys. Plasmas 16, 052704 (2009) (11 pages)

Online Publication Date: 19 May 2009

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As multi-keV x-ray radiators, hohlraums and halfraums with inner walls coated with metallic materials (called liner) have been tested for the first time with laser as the energy drive. For titanium, conversion efficiencies (CEs) are up to ~14% for emission into 4pi, integrating between 4.6 and 6.5 keV when a large diameter hohlraum is used. Germanium CE is ~0.8% into 4pi between 9 and 13 keV. The highest CEs have been obtained with a 1 ns squared pulse and phase plates giving laser absorption near 99%. These high CEs are due to long-lasting, good plasma conditions for multi-keV x-ray production maintained by plasma confinement inside the plastic cylinder and plasma collision leading to a burst of x rays at a time that depends on target size. As photon emitters at 4.7 keV, titanium-lined hohlraums are the most efficient solid targets and data are close to CEs for gas targets, which are considered as the upper limit for x-ray yields since their low density allows good laser absorption and low kinetics losses. As 10.3 keV x-ray emitters, exploded germanium foils give best results one order of magnitude more efficient than thick targets; doped aerogels and lined hohlraums give similar yields, about three times lower than those from exploded foils.
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07.85.Fv, 52.50.Jm, 52.25.Os

Ionospheric, Solar-System, and Astrophysical Plasmas

A statistical analysis of systematic errors in temperature and ram velocity estimates from satellite-borne retarding potential analyzers

J. H. Klenzing, G. D. Earle, R. A. Heelis, and W. R. Coley

Phys. Plasmas 16, 052901 (2009) (6 pages)

Online Publication Date: 4 May 2009

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The use of biased grids as energy filters for charged particles is common in satellite-borne instruments such as a planar retarding potential analyzer (RPA). Planar RPAs are currently flown on missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellites Program to obtain estimates of geophysical parameters including ion velocity and temperature. It has been shown previously that the use of biased grids in such instruments creates a nonuniform potential in the grid plane, which leads to inherent errors in the inferred parameters. A simulation of ion interactions with various configurations of biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, the simulation calculates collected flux from Maxwellian ion distributions with three-dimensional drift relative to the instrument. Perturbations in the performance of flight instrumentation relative to expectations from the idealized RPA flux equation are discussed. Both single grid and dual-grid systems are modeled to investigate design considerations. Relative errors in the inferred parameters for each geometry are characterized as functions of ion temperature and drift velocity.
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52.70.Ds, 94.05.-a, 02.60.-x, 02.70.Bf

Effects of varying magnetosheath flow and dissipation on the two-dimensional reconnection structure at the magnetopause

Lars G. Westerberg, Hans O. Åkerstedt, and J. Henric Taavola

Phys. Plasmas 16, 052902 (2009) (11 pages)

Online Publication Date: 18 May 2009

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The stationary Riemann problem including dissipation in form of resistivity and viscosity for the reconnection structure at the dayside magnetopause is considered. Including tangential velocity shear and gradients across the complete reconnection structure from the magnetosheath side into the magnetosphere, it is shown how dissipation affects the thickness of the intermediate shock wave in the vicinity of a reconnection site. We present how plasma flow structure undergoes a significant change for a nonzero uniform plasma velocity and velocity gradient. It is also shown how the reconnection rate changes and leads to a cutoff when the velocity becomes Alfvénic.
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94.30.ch, 94.30.cj, 94.30.cp, 52.35.Bj, 52.35.Vd, 52.40.Kh, 52.55.Tn

Magnetohydrodynamic study of three-dimensional instability of the spontaneous fast magnetic reconnection

T. Shimizu, K. Kondoh, K. Shibata, and M. Ugai

Phys. Plasmas 16, 052903 (2009) (12 pages)

Online Publication Date: 28 May 2009

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Three-dimensional instability of the spontaneous fast magnetic reconnection is studied with magnetohydrodynamic (MHD) simulation, where the two-dimensional model of the spontaneous fast magnetic reconnection is destabilized in three dimension. Generally, in two-dimensional magnetic reconnection models, every plasma condition is assumed to be uniform in the sheet current direction. In such two-dimensional MHD simulations, the current sheet destabilized by the initial resistive disturbance can be developed to fast magnetic reconnection by a current driven anomalous resistivity. In this paper, the initial resistive disturbance includes a small amount of fluctuations in the sheet current direction, i.e., along the magnetic neutral line. The other conditions are the same as that of previous two-dimensional MHD studies for fast magnetic reconnection. Accordingly, we may expect that approximately two-dimensional fast magnetic reconnection occurs in the MHD simulation. In fact, the fast magnetic reconnection activated on the first stage of the simulation is two dimensional. However, on the subsequent stages, it spontaneously becomes three dimensional and is strongly localized in the sheet current direction. The resulting three-dimensional fast magnetic reconnection intermittently ejects three-dimensional magnetic loops. Such intermittent ejections of the three-dimensional loops are similar to the intermittent downflows observed in the solar flares. The ejection of the three-dimensional loops seems to be random but, numerically and theoretically, it is shown that the aspect ratio of the ejected loops is limited under a criterion.
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52.35.Vd, 52.35.Py, 52.30.Cv, 52.25.Gj, 52.25.Fi, 52.65.Kj

Lasers, Particle Beams, Accelerators, Radiation Generation

Electromagnetic instability in an electron beam–ion channel system

D. Su and C. J. Tang

Phys. Plasmas 16, 053101 (2009) (5 pages)

Online Publication Date: 7 May 2009

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The transverse electromagnetic instability in the electron beam–ion channel system is investigated using kinetic theory. The equilibrium distribution function of a relativistic electron beam, which takes into account a strong ion channel effect, is obtained. The linearized Vlasov equation is solved and the dispersion relation of the system is derived by perturbing the equilibrium with a high frequency electromagnetic wave (EMW). Analysis of the dispersion relation shows that the coupling of the electron beam with the transverse high frequency EMW is achieved through the deflection of the beam electrons due to the synergistic effects of the transverse high frequency EMW and transverse betatron oscillation. The numerical calculation finds that a branch of slow wave instability (SWI) with a wide frequency band is excited. The attenuation index of the SWI increases and its frequency band broadens as the normalized beam radii increases. Besides, the SWI will be suppressed as the longitudinal velocity of the electron beam increases to a certain value; meanwhile, a bunch of fast wave instability (FWI) is excited, which is equal to the increase of the relativistic factor. Also both the SWI and the FWI reach maximum when the EMW frequency meets a resonance condition.
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52.35.-g, 52.35.Qz, 52.27.Ny

Cross-phase modulation between lasers in a tunnel ionizing gas

C. S. Liu, Vishwa Bandhu Pathak, and V. K. Tripathi

Phys. Plasmas 16, 053102 (2009) (6 pages)

Online Publication Date: 12 May 2009

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The phase modulation of a low power long pulse probe laser beam in a rapidly tunnel ionizing gas (helium) under a relativistic short pulse laser is investigated. The relativistic pulse creates a fast increasing plasma density at its front, far ahead of the intensity peak. The probe pulse sees these changes as modulation in its phase and undergoes large frequency upshift. The spectral content of the blueshifted potion of the probe pulse is large when its intensity peak commoves with the ionization front. There are two ionization front created by first and second ionizations, and the separation between the two increases as laser propagates through the gas. The rate of density variation by first and second ionizations, however, is fairly the same and varies little as the spot size of the laser beam increases up to three times its initial value. The ionization front velocity, as well as the upshift in probe pulse frequency, is bigger for sharper laser pulse.
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52.40.Db, 52.40.Mj, 52.70.-m, 52.27.Ny, 52.25.-b

Plasma expansion and fast gap closure in a high power electron beam diode

Amitava Roy, R. Menon, S. Mitra, Senthil Kumar, Vishnu Sharma, K. V. Nagesh, K. C. Mittal, and D. P. Chakravarthy

Phys. Plasmas 16, 053103 (2009) (9 pages)

Online Publication Date: 13 May 2009

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High power electron beam generation studies were carried out in a planar diode configuration to investigate the effect of the accelerating gap, diode voltage, and anode-cathode materials on the electrode plasma expansion. The diode voltage has been varied from 145–428 kV, whereas the current density has been varied from 208–2215  A/cm2 with 100 ns pulse duration. It was found that the diode voltage and current follow the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 11  cm/µs for 34 mm anode-cathode gap and the plasma velocity decreases for smaller gaps. It was found that the plasma expansion velocity increases significantly due to the cathode edge contribution and the edge contribution is particularly important during the beginning and the end of the accelerating pulse when the diode voltage and the corresponding electric field are comparatively low. It was also observed that the diode current increased by a factor of 3 when anode material was released into the accelerating gap due to the electron beam bombardment.
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52.59.Mv, 52.40.Mj, 52.50.-b

Nonlinear longitudinal compression of short laser pulses in the atmosphere

Burak Yedierler

Phys. Plasmas 16, 053104 (2009) (5 pages)

Online Publication Date: 14 May 2009

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Propagation of short and intense laser beams in the atmosphere is considered for the purpose of identifying the temporal compression. The conditions and validity of linear and nonlinear compression theories are discussed. The effects of chirping and pulse power in the preionization regime are deliberated. The fact that the linear theory cannot explain the pulse compression in the atmosphere is presented.
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52.25.Os, 92.60.Ta, 52.80.-s

Influence of subpicosecond laser pulse duration on proton acceleration

M. Carrié, E. Lefebvre, A. Flacco, and V. Malka

Phys. Plasmas 16, 053105 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: PDF (734 kB)

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The influence of pulse duration on proton acceleration using subpicosecond (30–300 fs), ultraintense (from 3.6×1018 to 3.6×1019  W/cm2), constant energy (0.14 J) laser pulses is studied using two-dimensional simulations. The entire pulse duration is modeled so that during the rising edge of the pulse a preplasma can naturally expand from the target front and rear surfaces into vacuum, altering respectively laser absorption and electrostatic field generation. In this paper, we study this effect for two target profiles (sharp-edge profile and smooth density gradient at the front side) and we point out the existence of a weak optimum pulse duration for proton acceleration. For the different pulse durations we consider, we first show that the maximum proton energy variations are similar to those of the rear side electrostatic field amplitude. The energy variations, however, are smaller than expected from the field variations, and we explain this effect by characteristic proton acceleration time.
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52.38.Kd, 52.38.Dx, 52.25.Os, 52.65.Rr

Vacuum electron acceleration by tightly focused laser pulses with nanoscale targets

K. I. Popov, V. Yu. Bychenkov, W. Rozmus, R. D. Sydora, and S. S. Bulanov

Phys. Plasmas 16, 053106 (2009) (9 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (989 kB)

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Electron acceleration using a tightly focused relativistic short laser pulse interacting with a spherical nanocluster, ultrathin foil or preformed mid-dense plasmas is studied by using three-dimensional particle-in-cell simulations with the Stratton–Chu integrals as the boundary conditions for the incident laser fields. The investigation is performed in the regime where the focal spot size is comparable with the laser wavelength. Generation of high-energy electron multibunch jets with quasimonoenergetic or waterbaglike spectra has been demonstrated. The physical process of acceleration and bunching of the electrons is discussed in detail, as well as particles energy and angular distributions for different laser intensities, focusing optics, target parameters, and laser incidence angles.
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52.38.Kd, 52.50.Jm, 52.65.Rr

Simple model for wakefield excitation by intense short-pulse laser in underdense plasma

Xin Wang (王鑫), Wei Yu (余玮), M. Y. Yu (郁明阳), Han Xu (徐涵), J. W. Wang (王精伟), and Xiao Yuan (袁孝)

Phys. Plasmas 16, 053107 (2009) (5 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (486 kB)

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A simple analytical model for intense-laser interaction with low-density plasma is used to investigate the dependence of the wake structure on the laser parameters and the background plasma density. Many of the properties observed in the existing multidimensional particle-in-cell simulations are qualitatively recovered.
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52.38.Kd, 52.25.Os, 52.65.Rr

Radiation: Emission, Absorption, Transport

Neutron and high energy deuteron anisotropy investigations in plasma focus device

M. V. Roshan, R. S. Rawat, A. Talebitaher, P. Lee, and S. V. Springham

Phys. Plasmas 16, 053301 (2009) (4 pages)

Online Publication Date: 15 May 2009

Full Text: PDF (189 kB)

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The anisotropies of neutron and high energy deuteron emissions from the NX2 plasma focus device [M. V. Roshan et al., Phys. Lett. A 373, 851 (2009)] are studied. The nuclear activation of graphite targets is used to measure the fluences of high energy deuterons in the axial and radial directions. Two bismuth germanate scintillation detectors connected to multichannel analyzer systems are used for the detection of 511 keV gamma rays resulting from positron annihilation in the two targets. In addition, fast neutron activation detectors are employed to measure the axial and radial fluences of fusion neutrons. These detection systems are calibrated using the simulation code MCNPX [L. S. Waters et al., AIP Conf. Proc. 896, 81 (2007)]. Two distinct regimes of neutron and deuteron anisotropies are observed for the NX2 device. For deuterium gas pressures below 10 mbar, the neutron anisotropy increases with increasing pressure, while the overall neutron yield remains low. For gas pressures of 10–14 mbar, the neutron anisotropy is essentially constant, while, with increasing pressure, the neutron yield rises rapidly and the deuteron anisotropy falls.
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52.58.Lq, 52.59.Hq, 29.40.Mc, 13.66.-a, 52.25.Tx

Low-Temperature Plasmas, Plasma Applications, Plasma Sources, Sheaths

Particle-in-cell modeling of magnetized argon plasma flow through small mechanical apertures

Adam B. Sefkow and Samuel A. Cohen

Phys. Plasmas 16, 053501 (2009) (13 pages)

Online Publication Date: 1 May 2009

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Motivated by observations of supersonic argon-ion flow generated by linear helicon-heated plasma devices, a three-dimensional particle-in-cell (PIC) code is used to study whether stationary electrostatic layers form near mechanical apertures intersecting the flow of magnetized plasma. By self-consistently evaluating the temporal evolution of the plasma in the vicinity of the aperture, the PIC simulations characterize the roles of the imposed aperture and applied magnetic field on ion acceleration. The PIC model includes ionization of a background neutral-argon population by thermal and superthermal electrons, the latter found upstream of the aperture. Near the aperture, a transition from a collisional to a collisionless regime occurs. Perturbations of density and potential, with millimeter wavelengths and consistent with ion acoustic waves, propagate axially. An ion acceleration region of length ~200lambdaD,e–300lambdaD,e forms at the location of the aperture and is found to be an electrostatic double layer, with axially separated regions of net positive and negative charge. Reducing the aperture diameter or increasing its length increases the double layer strength.
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52.30.-q, 52.50.-b, 52.65.-y, 52.75.-d

The effect of N2 flow rate on discharge characteristics of microwave electron cyclotron resonance plasma

Wan-Yu Ding, Jun Xu, Wen-Qi Lu, Xin-Lu Deng, and Chuang Dong

Phys. Plasmas 16, 053502 (2009) (5 pages)

Online Publication Date: 6 May 2009

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The properties of plasma in Ar/N2 microwave electron cyclotron resonance discharge with a percentage of N2 flow rate ranging from 5% to 50% have been studied in order to understand the effect of N2 flow rate on the mechanical properties of silicon nitride films. N2+ radicals as well as N2, N+ are found by optical emission spectroscopy analysis. The evolution of plasma density, electron kinetic energy, N2+, N2, and N+ emission lines from mixed Ar/N2 plasma on changing mixture ratio has been studied. The mechanisms of their variations have been discussed. Moreover, an Ar/N2 flow ratio of 2/20 is considered to be the best condition for synthesizing a-Si3N4, which has been confirmed in the as-deposited silicon nitride films with quite good mechanical properties by nanoindentation analyses.
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52.25.Os, 52.70.Kz, 52.77.Dq, 68.60.Bs, 81.15.Jj, 68.55.aj

Mean free paths and elastic and related transport cross sections for neutrals and singly charged ions of Li, Be, and B in hydrogen plasmas

P. S. Krstić and D. R. Schultz

Phys. Plasmas 16, 053503 (2009) (6 pages)

Online Publication Date: 7 May 2009

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The mean free paths are computed from the momentum transfer cross sections associated with collisions of protons with Li, Be, and B and for Li, Li+, Be+, and B+ colliding with atomic hydrogen, for center of mass energies between 0.0001 and 10 000 eV. The elastic and viscosity cross sections are also calculated for these collision systems. A fully quantum mechanical approach has been used up to 100 eV along with a more approximate, quasiclassical method between ~0.1 and 10 000 eV.
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52.20.-j

Signature of fast H atoms from cathode glow region of a dc discharge

P. Bharathi, K. S. Suraj, V. Prahlad, S. Mukherjee, and P. Vasu

Phys. Plasmas 16, 053504 (2009) (10 pages)

Online Publication Date: 12 May 2009

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Asymmetric broadening of Halpha line from cathode glow region has been studied. In the cathode glow, mean energy and fractional population of very fast hydrogen atoms were found to be ~130  eV and ~55%, respectively. These values reduced to ~90  eV and ~20% when measured at negative glow region. The observed asymmetry was attributed to the presence of the fast hydrogen atoms near the cathode surface. The mean energy and number density of excited fast hydrogen atoms were estimated from the velocity distribution of H+, H<sub>2</sub><sup>+</sup>, and H<sub>3</sub><sup>+</sup> considering collisions inside the cathode sheath. The reduction in the mean energy and number density of the excited fast hydrogen atoms, at the other locations of the discharge, was explained by energy relaxation and thermalization of the neutrals with the background gas.
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52.80.Hc, 52.20.Hv, 52.40.Kh, 32.70.Jz

Effective control of ion fluxes over large areas by magnetic fields: From narrow beams to highly uniform fluxes

O. Baranov, M. Romanov, and Kostya (Ken) Ostrikov

Phys. Plasmas 16, 053505 (2009) (5 pages)

Online Publication Date: 12 May 2009

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An effective control of the ion current distribution over large-area (up to 103  cm2) substrates with the magnetic fields of a complex structure by using two additional magnetic coils installed under the substrate exposed to vacuum arc plasmas is demonstrated. When the magnetic field generated by the additional coils is aligned with the direction of the magnetic field generated by the guiding and focusing coils of the vacuum arc source, a narrow ion density distribution with the maximum current density 117  A m−2 is achieved. When one of the additional coils is set to generate the magnetic field of the opposite direction, an area almost uniform over the substrate of 103  cm2 ion current distribution with the mean value of 45  A m−2 is achieved. Our findings suggest that the system with the vacuum arc source and two additional magnetic coils can be effectively used for the effective, high throughput, and highly controllable plasma processing.
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52.77.-j, 52.80.Mg

The influence of space charge shielding on dielectric multipactor

C. Chang, G. Z. Liu, C. X. Tang, and L. X. Yan

Phys. Plasmas 16, 053506 (2009) (6 pages)

Online Publication Date: 28 May 2009

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A model of space charge influenced by multipactor electrons and plasma has been established. The positive space charge potential/field for vacuum dielectric multipactor is analytically studied. After considering the plasma, the positive space charge field is further shielded, and multipactor saturates at higher surface accumulated field, compared with that for only considering multipactor electrons. The negative space charge potential/field for dielectric breakdown at high pressure is analyzed. It is found that the negative potential can be nonmonotonously varied, forming a minimum potential well.
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52.80.Pi, 52.40.Mj, 52.25.Fi, 52.25.Dg, 02.60.Lj

Competitive effects of an axial magnetic field and of neutral gas depletion in a positive column

L. Liard, J.-L. Raimbault, and P. Chabert

Phys. Plasmas 16, 053507 (2009) (8 pages)

Online Publication Date: 29 May 2009

Full Text: PDF (344 kB)

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Neutral gas dynamics has been incorporated in plasma transport equations in recent studies of nonmagnetized plasma discharge equilibrium. It was found that when the plasma density increases, the neutral gas density becomes depleted in the discharge center, leading to plasma deconfinement. Consequently, larger electron temperature, flatter plasma density profiles, and larger edge-to-center plasma density ratios were observed. In this paper, we investigate the effect of adding a static axial magnetic field to the discharge. We find that at fixed plasma density at the center, the magnetic field reduces the calculated neutral depletion and all the associated effects. Nevertheless, the action of the magnetic field is less pronounced if one keeps the power deposited into the discharge fixed instead. This is because at fixed power, the plasma density increases with the magnetic field.
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52.80.Vp, 52.25.Ya, 52.25.Xz, 52.30.Ex

Dusty Plasmas

Weakly nonlinear dust ion-acoustic shock waves in a dusty plasma with nonthermal electrons

Abderrezak Berbri and Mouloud Tribeche

Phys. Plasmas 16, 053701 (2009) (5 pages)

Online Publication Date: 1 May 2009

Full Text: PDF (202 kB)

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Weakly nonlinear dust ion-acoustic (DIA) shock waves are investigated in a dusty plasma with nonthermal electrons. A modified Korteweg–de Vries equation with a cubic nonlinearity is derived. Due to the net negative dust charge µZd and electron nonthermality, the present plasma model can admit compressive and rarefactive weak DIA shock waves. The effect of increasing µZd is to lower the critical nonthermal parameter betac above which only rarefactive DIA shock waves are admitted. Our investigation may help to understand the nonlinear structures observed in the auroral acceleration regions.
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52.27.Lw, 52.35.Mw, 52.35.Tc

Acceleration of soliton by nonlinear Landau damping of dust-helical waves

Zahida Ehsan, Nodar L. Tsintsadze, J. Vranjes, and S. Poedts

Phys. Plasmas 16, 053702 (2009) (7 pages)

Online Publication Date: 6 May 2009

Full Text: PDF (149 kB)

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The problem of nonlinear Landau damping of helicon waves in dusty plasma in particular emphasis to the acceleration of soliton is presented here. This in the framework of a collisionless, anisotropic homogeneous dusty plasma in one dimension, can be well described by two coupled dynamical equations of the generalized Zakharov type, with one extra nonlocal term coming from Landau damping. Nonlinear-nonlocal term gives rise to essential contributions relative to the local term. Then under different conditions, kinetic nonlinear Schrödinger equation is constructed and nonlinear decrement is obtained for two cases. It is noticed that the time dependant term in the ponderomotive force plays a significant role for this kind of damping. Additionally, it is shown that nonlinear Landau damping leads to the amplitude modulation of dust helicon waves, further modulational instability, and maximal growth rate is obtained when the group velocity of the helicon wave reaches the dust-acoustic speed. It is demonstrated that how the nonlinear Landau damping leads to the acceleration of soliton, which is eventually slowed down after transferring some of its energy to the wave. Emission of dust-acoustic wave by accelerated soliton is discussed briefly.
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52.35.Sb, 52.35.Fp, 52.35.Py, 52.27.Lw

A Korteweg–de Vries Burgers-like equation for weakly nonlinear dust ion-acoustic waves in a charge-varying dusty plasma with nonthermal electrons

Abderrezak Berbri and Mouloud Tribeche

Phys. Plasmas 16, 053703 (2009) (8 pages)

Online Publication Date: 14 May 2009

Full Text: PDF (469 kB)

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A weakly nonlinear analysis is carried out to derive a Korteweg–de Vries Burgers-like equation for small but finite amplitude dust ion-acoustic (DIA) waves in a charge varying dusty plasma with non thermally distributed electrons. The correct expression for the nonthermal electron charging current is used. Interestingly, it may be noted that due to electron nonthermality and finite equilibrium ion streaming velocity, the present dusty plasma model can admit compressive as well as rarefactive DIA solitary waves. Furthermore, there may exist DIA shocks which have either monotonic or oscillatory behavior and the properties of which depend sensitively on the number of fast nonthermal electrons. Our results should be useful to understand the properties of localized DIA waves that may occur in space dusty plasmas.
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52.27.Lw, 52.35.Fp, 52.35.Mw, 52.35.Tc

Nonlinear dust-acoustic waves in a strongly coupled dusty plasma with vortexlike ion distribution

M. G. M. Anowar, M. S. Rahman, and A. A. Mamun

Phys. Plasmas 16, 053704 (2009) (5 pages)

Online Publication Date: 18 May 2009

Full Text: PDF (746 kB)

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The nonlinear features of dust-acoustic (DA) waves in a strongly coupled unmagnetized dusty plasma (containing electrons following Boltzmann distribution, ions obeying vortexlike distribution, and negatively charged mobile dust) are investigated by using reductive perturbation method. It is observed that the nonlinear propagation of the DA waves gives rise to solitary structures when the strong correlation is absent and gives rise to shock structures when the strong correlation among the dust grains is present. The condition for the formation of oscillatory and monotonic shock structures is also found. The implications of our result in space and laboratory dusty plasmas are discussed.
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52.27.Lw, 52.35.Sb, 52.35.We, 52.35.Fp, 52.35.Tc, 52.35.Mw

Brownian dynamics of charged particles in a constant magnetic field

L. J. Hou, Z. L. Mišković, A. Piel, and P. K. Shukla

Phys. Plasmas 16, 053705 (2009) (12 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (1445 kB)

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Numerical algorithms are proposed for simulating the Brownian dynamics of charged particles in an external magnetic field, taking into account the Brownian motion of charged particles, damping effect, and the effect of magnetic field self-consistently. Performance of these algorithms is tested in terms of their accuracy and long-time stability by using a three-dimensional Brownian oscillator model with constant magnetic field. Step-by-step recipes for implementing these algorithms are given in detail. It is expected that these algorithms can be directly used to study particle dynamics in various dispersed systems in the presence of a magnetic field, including polymer solutions, colloidal suspensions, and, particularly, complex (dusty) plasmas. The proposed algorithms can also be used as thermostat in the usual molecular dynamics simulation in the presence of magnetic field.
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52.40.Hf, 52.25.Vy, 05.40.-a

Modulated transverse off-plane dust-lattice wave packets in hexagonal two-dimensional dusty plasma crystals

B. Farokhi, M. Shahmansouri, and I. Kourakis

Phys. Plasmas 16, 053706 (2009) (11 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (521 kB)

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The propagation of nonlinear dust-lattice waves in a two-dimensional hexagonal crystal is investigated. Transverse (off-plane) dust grain oscillatory motion is considered in the form of a backward propagating wave packet whose linear and nonlinear characteristics are investigated. An evolution equation is obtained for the slowly varying amplitude of the first (fundamental) harmonic by making use of a two-dimensional lattice multiple scales technique. An analysis based on the continuum approximation (spatially extended excitations compared to the lattice spacing) shows that wave packets will be modulationally stable and that dark-type envelope solitons (density holes) may occur in the long wavelength region. Evidence is provided of modulational instability and of the occurrence of bright-type envelopes (pulses) at shorter wavelengths. The role of second neighbor interactions is also investigated and is shown to be rather weak in determining the modulational stability region. The effect of dissipation, assumed negligible in the algebra throughout the article, is briefly discussed.
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52.27.Lw, 05.45.Yv, 63.20.Ry

Generation of two-dimensional dust vortex flows in a direct current discharge plasma

Giichiro Uchida, Satoru Iizuka, Tetsuo Kamimura, and Noriyoshi Sato

Phys. Plasmas 16, 053707 (2009) (6 pages)

Online Publication Date: 21 May 2009

Full Text: PDF (781 kB)

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The two-dimensional dust vortex flows are observed in a direct current discharge plasma near the edge of a metal plate which is situated in the dust-particle levitation region. Applying negative dc potential to the metal plate, dust particles are strongly accelerated toward the metal plate edge, and two symmetric dust vortex flows are generated on both sides of the metal plate. Numerical calculation including the effect of the ion drag force well demonstrates the dust vortex formation as in the experiment. A mechanism of the dust vortex generation could be explained by effect of an asymmetry of ion drag force near the metal plate.
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52.27.Lw
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BRIEF COMMUNICATIONS

On Coulomb collisions in bi-Maxwellian plasmas

Petr Hellinger and Pavel M. Trávníček

Phys. Plasmas 16, 054501 (2009) (4 pages)

Online Publication Date: 18 May 2009

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Collisional momentum and energy transport in bi-Maxwellian plasmas with a drift velocity along the ambient magnetic field are calculated from both the Fokker–Planck and Boltzmann integral approximations. The transport coefficients obtained from the two approaches are identical to the leading order (proportional to the Coulomb logarithm) and are presented here in a closed form involving generalized double hypergeometric functions.
Show PACS
52.25.Fi, 52.65.Ff

Test charge potential in the presence of electron acoustic waves in multispecies dusty plasma

S. Ali

Phys. Plasmas 16, 054502 (2009) (3 pages)

Online Publication Date: 20 May 2009

Full Text: PDF (106 kB)

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An expression for the test charge potential is obtained in a multispecies dusty plasma, whose constituents are the Boltzmann distributed hot electrons, mobile cold electrons, immobile cold ions, and charge fluctuating isolated dust grains. The plasma response function involving the electron-acoustic waves becomes modified due to the inclusion of the dust-charge perturbations. The analytical and numerical investigations reveal that the Debye–Hückel screening and wakefield potentials are significantly affected by the plasma parameters such as the equilibrium dust number density, the dust grain radius, and the hot electron temperature. The relevance of the results to laboratory plasma, where the two distinct groups of electrons exist besides the static ions and isolated dust grains, is discussed.
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52.27.Lw, 52.35.-g, 52.25.-b

On nonresonant proton heating via intrinsic Alfvénic turbulence

C. S. Wu, P. H. Yoon, and C. B. Wang

Phys. Plasmas 16, 054503 (2009) (3 pages)

Online Publication Date: 29 May 2009

Full Text: PDF (71 kB)

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In a recent publication Wu and Yoon [Phys. Rev. Lett. 99, 075001 (2007)] propose that low-beta protons may be heated by turbulent Alfvén waves via nonresonant wave-particle scattering. The present Brief Communication clarifies some conceptual issues and describes the theoretical methods adopted in the above reference in more detail.
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52.35.Ra, 52.35.Bj, 52.30.Cv, 52.25.Fi
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COMMENTS

FREE

Comment on “Plasma ionization by annularly bounded helicon waves” [Phys. Plasmas 13, 063501 (2006)]

Robert W. Johnson

Phys. Plasmas 16, 054701 (2009) (3 pages)

Online Publication Date: 4 May 2009

Full Text: PDF (87 kB)

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The neoclassical calculation of the helicon wave theory contains a fundamental flaw. Use is made of a proportional relationship between the magnetic field and its curl to derive the Helmholtz equation describing helicon wave propagation. However, by the fundamental theorem of Stokes, the curl of the magnetic field must be perpendicular to that portion of the field contributing to the local curl. Re-examination of the equations of motion indicates that only electromagnetic waves propagate through a stationary region of constant pressure in a fully ionized, neutral medium.
Show PACS
52.25.Jm, 52.50.Dg, 52.40.Fd
FREE

Response to “Comment on `Plasma ionization by annularly bounded helicon waves' ” [Phys. Plasmas 16, 044701 (2009)]

Mitchell L. R. Walker and Masayuki Yano

Phys. Plasmas 16, 054702 (2009) (1 page)

Online Publication Date: 4 May 2009

Full Text: PDF (32 kB)

+
 Abstract Unavailable
Show PACS
52.35.-g, 52.55.Fa, 52.40.Fd, 52.25.Fi, 52.50.Dg, 52.40.Hf
FREE

Comment on “Quantum correction to Landau damping of electron plasma waves” [Phys. Plasmas 16, 032105 (2009)]

Jian Zheng

Phys. Plasmas 16, 054703 (2009) (1 page)

Online Publication Date: 11 May 2009

Full Text: PDF (45 kB)

+
 Abstract Unavailable
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52.35.-g, 52.25.Mq
FREE

Response to “Comment on `Quantum correction to Landau damping of electron plasma waves' ” [Phys. Plasmas 16, 054703 (2009)]

Jun Zhu, Peiyong Ji, and Nan Lu

Phys. Plasmas 16, 054704 (2009) (1 page)

Online Publication Date: 11 May 2009

Full Text: PDF (46 kB)

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We present three arguments to demonstrate that the comment on our paper [J. Zhu, P. Ji, and N. Lu, Phys. Plasmas 16, 032105 (2009)] by Zheng is incorrect, and the validity and feasibility of our start point are confirmed in this response.
Show PACS
52.25.Fi, 52.20.Fs, 52.35.-g, 52.65.Ff
FREE

Comment on “The single-wall carbon nanotube waveguides and excitation of their sigma+pi plasmons by an electron beam” [Phys. Plasmas 16, 022108 (2009)]

Afshin Moradi

Phys. Plasmas 16, 054705 (2009) (1 page)

Online Publication Date: 12 May 2009

Full Text: PDF (49 kB)

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In a recent article [M. Nejati, C. Javaherian, B. Shokri, and B. Jazi, Phys. Plasmas 16, 022108 (2009)], Nejati et al. studied the propagation of plasma wave in the single-wall carbon nanotubes in the presence of the electron beam and showed that the frequency of the sigma+pi plasma wave strongly depends on the nanotube radius in the short-wavelength region. Here we derive the correct form of the dispersion relation for the transverse magnetic wave in the system and show that the frequency of the plasma wave is quite sensitive to the radius of the tube in the long-wavelength limit.
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52.35.-g
FREE

Response to “Comment on `The single-wall carbon nanotube waveguides and excitation of their sigma+pi plasmons by an electron beam' ” [Phys. Plasmas 16, 054705 (2009)]

M. Nejati, C. Javaherian, B. Shokri, and B. Jazi

Phys. Plasmas 16, 054706 (2009) (1 page)

Online Publication Date: 12 May 2009

Full Text: PDF (46 kB)

+
 Abstract Unavailable
Show PACS
52.40.Fd, 52.40.Mj
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PAPERS FROM THE 50TH ANNUAL MEETING OF THE APS DIVISION OF PLASMA PHYSICS

FREE

Foreword to Special Issue: Papers from the 50th Annual Meeting of the APS Division of Plasma Physics, Dallas, Texas, 2008

Amitava Bhattacharjee and Ronald C. Davidson

Phys. Plasmas 16, 055301 (2009) (1 page)

Online Publication Date: 27 April 2009

Full Text: PDF (35 kB)

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The year 2008 marked the 50th Anniversary of the Division of Plasma Physics (DPP) of the American Physical Society. This Special Issue presents many of the Review, Tutorial, and Invited papers that were presented at the 2008 Annual Meeting of the DPP, which was held 17–21 November, in Dallas, Texas. We are very pleased that many of the speakers have submitted an archival-quality version of their presentation for peer review and publication in Physics of Plasmas.
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01.30.-y, 52.00.00
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REVIEW PAPERS

Perspectives on high-energy-density physics

R. P. Drake

Phys. Plasmas 16, 055501 (2009) (7 pages)

Online Publication Date: 6 March 2009

Full Text: PDF (758 kB)

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Much of 21st century plasma physics will involve work to produce, understand, control, and exploit very nontraditional plasmas. High-energy-density (HED) plasmas are often examples, variously involving strong Coulomb interactions and <<1 particles per Debye sphere, dominant radiation effects, and strongly relativistic or strongly quantum-mechanical behavior. Indeed, these and other modern plasma systems often fall outside the early standard theoretical definitions of “plasma.” Here the specific ways in which HED plasmas differ from traditional plasmas are discussed. This is first done by comparison of important physical quantities across the parameter regime accessible by existing or contemplated experimental facilities. A specific discussion of some illustrative cases follows, including strongly radiative shocks and the production of relativistic, quasimonoenergetic beams of accelerated electrons.
Show PACS
52.50.Jm, 52.35.Tc, 52.25.-b, 52.50.Lp
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INVITED PAPERS

Basic Plasma Phenomena, Waves, Instabilities

Quantitative analytical model for magnetic reconnection in Hall magnetohydrodynamics

Andrei N. Simakov and L. Chacón

Phys. Plasmas 16, 055701 (2009) (10 pages)

Online Publication Date: 11 February 2009

Full Text: PDF (295 kB)

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Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or “fast”) reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths di has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on di.
Show PACS
52.35.Vd, 52.30.Cv, 52.25.Fi

Plasma structures observed in gas breakdown using a 1.5 MW, 110 GHz pulsed gyrotron

Yoshiteru Hidaka, E. M. Choi, I. Mastovsky, M. A. Shapiro, J. R. Sirigiri, R. J. Temkin, G. F. Edmiston, A. A. Neuber, and Y. Oda

Phys. Plasmas 16, 055702 (2009) (7 pages)

Online Publication Date: 12 March 2009

Full Text: PDF (1214 kB)

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Regular two-dimensional plasma filamentary arrays have been observed in gas breakdown experiments using a pulsed 1.5 MW, 110 GHz gyrotron. The gyrotron Gaussian output beam is focused to an intensity of up to 4  MW/cm2. The plasma filaments develop in an array with a spacing of about one quarter wavelength, elongated in the electric field direction. The array was imaged using photodiodes, a slow camera, which captures the entire breakdown event, and a fast camera with a 6 ns window. These diagnostics demonstrate the sequential development of the array propagating back toward the source. Gases studied included air, nitrogen, SF6, and helium at various pressures. A discrete plasma array structure is observed at high pressure, while a diffuse plasma is observed at lower pressure. The propagation speed of the ionization front for air and nitrogen at atmospheric pressure for 3  MW/cm2 was found to be of the order of 10 km/s.
Show PACS
52.80.-s, 52.35.Py, 52.70.Kz

Langmuir probe-based observables for plasma-turbulence code validation and application to the TORPEX basic plasma physics experiment

Paolo Ricci, C. Theiler, A. Fasoli, I. Furno, B. Labit, S. H. Müller, M. Podestà, and F. M. Poli

Phys. Plasmas 16, 055703 (2009) (11 pages)

Online Publication Date: 18 March 2009

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The methodology for plasma-turbulence code validation is discussed, with focus on the quantities to use for the simulation-experiment comparison, i.e., the validation observables, and application to the TORPEX basic plasma physics experiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. The considered validation observables are deduced from Langmuir probe measurements and are ordered into a primacy hierarchy, according to the number of model assumptions and to the combinations of measurements needed to form each of them. The lowest levels of the primacy hierarchy correspond to observables that require the lowest number of model assumptions and measurement combinations, such as the statistical and spectral properties of the ion saturation current time trace, while at the highest levels, quantities such as particle transport are considered. The comparison of the observables at the lowest levels in the hierarchy is more stringent than at the highest levels. Examples of the use of the proposed observables are applied to a specific TORPEX plasma configuration characterized by interchange-driven turbulence.
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52.35.Ra, 52.70.Ds, 52.25.Fi, 52.65.-y

Structure of the dissipation region in fluid simulations of asymmetric magnetic reconnection

P. A. Cassak and M. A. Shay

Phys. Plasmas 16, 055704 (2009) (11 pages)

Online Publication Date: 24 March 2009

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The structure of the dissipation region during asymmetric magnetic reconnection is studied assuming antiparallel magnetic fields in two dimensions. A physics-based prediction for the scaling of the thickness of the dissipation region in (collisionless) Hall reconnection is presented and confirmed with two-fluid simulations. However, the substructure of the dissipation region in these and additional single-fluid (magnetohydrodynamics) simulations disagrees with a recent model [Cassak and Shay, Phys. Plasmas 14, 102114 (2007)]. We attribute the disagreement to the lack of plasma mixing along newly reconnected field lines in fluid models, rendering the use of a fluid description of questionable validity for determining the dissipation region substructure. Applications to the dayside magnetopause are discussed.
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52.30.Cv, 94.30.cp, 94.30.ch

Electron acoustic waves in pure ion plasmas

F. Anderegg, C. F. Driscoll, D. H. E. Dubin, T. M. O'Neil, and F. Valentini

Phys. Plasmas 16, 055705 (2009) (7 pages)

Online Publication Date: 8 April 2009

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Standing electron acoustic waves (EAWs) are observed in a pure ion plasma. EAWs are slow nonlinear plasma waves; at small amplitude their phase velocities (vph~=1.4[overline v] for small klambdaD) and their frequencies are in agreement with theory. At moderate amplitude, EAW-type plasma waves can be excited over a broad range of frequencies. This frequency variability comes from the plasma adjusting its velocity distribution so as to make the plasma mode resonant with the drive frequency. Wave-coherent laser-induced fluorescence shows the intimate nature of the wave-particle interaction, and how the particle distribution function is modified by the wave driver until the plasma mode is resonant with the driver.
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52.35.Fp, 52.35.Mw, 52.35.Dm, 52.70.Kz

Doppler-shifted cyclotron resonance of fast ions with circularly polarized shear Alfvén waves

Yang Zhang, W. W. Heidbrink, Shu Zhou, H. Boehmer, R. McWilliams, T. A. Carter, S. Vincena, and M. K. Lilley

Phys. Plasmas 16, 055706 (2009) (7 pages)

Online Publication Date: 16 April 2009

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The Doppler-shifted cyclotron resonance between fast ions and shear Alfvén waves (SAWs) has been experimentally investigated with a test-particle fast-ion (Li+) beam launched in the helium plasma of the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. Left- or right-hand circularly polarized SAWs are launched by an antenna with four current channels. A collimated fast-ion energy analyzer characterizes the resonance by measuring the nonclassical spreading of the averaged beam signal. Left-hand circularly polarized SAWs resonate with the fast ions but right-hand circularly polarized SAWs do not. The measured fast-ion profiles are compared with simulations by a Monte Carlo Lorentz code that uses the measured wave field data.
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52.35.Bj, 52.40.Fd, 52.65.Pp

Collisionless plasma expansion into vacuum: Two new twists on an old problem

Alexey V. Arefiev and Boris N. Breizman

Phys. Plasmas 16, 055707 (2009) (11 pages)

Online Publication Date: 22 April 2009

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The paper deals with a generic problem of collisionless plasma expansion into vacuum in the regimes where the expanding plasma consists of hot electrons and cold ions. The expansion is caused by electron pressure and serves as an energy transfer mechanism from electrons to ions. This process is often described under the assumption of Maxwellian electrons, which easily fails in the absence of collisions. The paper discusses two systems with a naturally occurring non-Maxwellian distribution: an expanding laser-irradiated nanoplasma and a supersonic jet coming out of a magnetic nozzle. The presented rigorous kinetic description demonstrates how the deviation from the Maxwellian distribution fundamentally alters the process of ion acceleration during plasma expansion. This result points to the critical importance of a fully kinetic treatment in problems with collisionless plasma expansion.
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52.38.Kd, 52.20.Hv, 52.20.Fs, 52.25.Dg