Volume 20, Issue 7, July 2013

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory includes a precision laser system now capable of delivering 1.8 MJ at 500 TW of 0.35μm light to a target. NIF has been operational since March 2009. A variety of experiments have been completed in support of NIF's mission areas: national security, fundamental science, and inertial fusion energy. NIF capabilities and infrastructure are in place to support its missions with nearly 60 Xray, optical, and nuclear diagnostic systems. A primary goal of the National Ignition Campaign (NIC) on the NIF was to implode a lowZ capsule filled with ∼0.2 mg of deuteriumtritium (DT) fuel via laser indirectdrive inertial confinement fusion and demonstrate fusion ignition and propagating thermonuclear burn with a net energy gain of ∼5–10 (fusion yield/input laser energy). This requires assembling the DT fuel into a dense shell of ∼1000 g/cm^{3} with an areal density (ρR) of ∼1.5 g/cm^{2}, surrounding a lower density hot spot with a temperature of ∼10 keV and a ρR ∼0.3 g/cm^{2}, or approximately an αparticle range. Achieving these conditions demand precise control of laser and target parameters to allow a low adiabat, high convergence implosion with low ablator fuel mix. We have demonstrated implosion and compressed fuel conditions at ∼80–90% for most point design values independently, but not at the same time. The nuclear yield is a factor of ∼3–10× below the simulated values and a similar factor below the alpha dominated regime. This paper will discuss the experimental trends, the possible causes of the degraded performance (the offset from the simulations), and the plan to understand and resolve the underlying physics issues.
 REVIEW ARTICLE


Progress towards ignition on the National Ignition Facility^{a)}
View Description Hide DescriptionThe National Ignition Facility (NIF) at Lawrence Livermore National Laboratory includes a precision laser system now capable of delivering 1.8 MJ at 500 TW of 0.35μm light to a target. NIF has been operational since March 2009. A variety of experiments have been completed in support of NIF's mission areas: national security, fundamental science, and inertial fusion energy. NIF capabilities and infrastructure are in place to support its missions with nearly 60 Xray, optical, and nuclear diagnostic systems. A primary goal of the National Ignition Campaign (NIC) on the NIF was to implode a lowZ capsule filled with ∼0.2 mg of deuteriumtritium (DT) fuel via laser indirectdrive inertial confinement fusion and demonstrate fusion ignition and propagating thermonuclear burn with a net energy gain of ∼5–10 (fusion yield/input laser energy). This requires assembling the DT fuel into a dense shell of ∼1000 g/cm^{3} with an areal density (ρR) of ∼1.5 g/cm^{2}, surrounding a lower density hot spot with a temperature of ∼10 keV and a ρR ∼0.3 g/cm^{2}, or approximately an αparticle range. Achieving these conditions demand precise control of laser and target parameters to allow a low adiabat, high convergence implosion with low ablator fuel mix. We have demonstrated implosion and compressed fuel conditions at ∼80–90% for most point design values independently, but not at the same time. The nuclear yield is a factor of ∼3–10× below the simulated values and a similar factor below the alpha dominated regime. This paper will discuss the experimental trends, the possible causes of the degraded performance (the offset from the simulations), and the plan to understand and resolve the underlying physics issues.
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 LETTERS


Plasmonic Roche lobe in metaldielectricmetal structure
View Description Hide DescriptionThis study investigates a plasmonic Roche lobe that is based on a metaldielectricmetal (MDM) structure using finitedifference timedomain simulations and theoretical analyses. The effective refractive index of the MDM structure has two centers and is inversely proportional to the distance from the position of interest to the centers, in a manner that is analogous to the gravitational potential in a twostar system. The motion of surface plasmons (SPs) strongly depends on the ratio of permittivities at the two centers. The Lagrange point is an unstable equilibrium point for SPs that propagate in the system. After the SPs have passed through the Lagrange point, their spread drastically increases.

Anisotropy of radiation emitted from planar wire arrays
View Description Hide DescriptionThe planar wire array (PWA) is a promising load for new multisource inertial confinement fusion (ICF) hohlraums [B. Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The hohlraum radiation symmetry is an important issue for ICF. It was found that extreme ultraviolet and subkeV photon emission from PWAs may have considerable anisotropy in the load azimuthal plane. This experimental result is obtained on the UNR 1–1.7 MA Zebra generator. The timedependent anisotropy effect is detected. This feature is studied in 2D numerical simulations and can be explained by initial anisotropy of implosion of those noncylindrical loads radiating essentially as surface sources in subkeV quanta and also by radiation absorption in cold magnetized plasma tails forming in the direction of magnetic compression.

Enhancement of proton acceleration field in laser doublelayer target interaction
View Description Hide DescriptionA mechanism is proposed to enhance a proton acceleration field in laser plasma interaction. A doublelayer plasma with different densities is illuminated by an intense short pulse. Electrons are accelerated to a high energy in the first layer by the wakefield. The electrons accelerated by the laser wakefield induce the enhanced target normal sheath (TNSA) and breakout afterburner (BOA) accelerations through the second layer. The maximum proton energy reaches about 1 GeV, and the total charge with an energy higher than 100 MeV is about several tens of μC/μm. Both the acceleration gradient and laser energy transfer efficiency are higher than those in singletargetbased TNSA or BOA. The model has been verified by 2.5DPIC simulations.
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 ARTICLES

 Basic Plasma Phenomena, Waves, Instabilities

Density modification by two superposing TE_{10} modes in a plasma filled rectangular waveguide
View Description Hide DescriptionMicrowave and plasma interaction is examined via two fundamental TE10 modes propagating in a plasma filled rectangular waveguide after superposing at a smaller angle. The propagation of the resultant mode realized from these two modes is governed by a wave equation obtained using the Maxwell's equations. This equation is solved numerically using fourth order RungeKutta method for the field amplitude of the microwave in the waveguide considering the waveguide to be made up of a perfect conductor and filled with different types of initial plasma density distributions, viz. homogeneous density, linear density with gradient in the propagation direction, and the density with Gaussian profile along the waveguide width. A phenomenon similar to the duct formation by high power microwaves is found to take place, where the plasma density attains interesting profiles. These profiles can be controlled by the angle of superposition, phase difference between the fields of the two modes, microwave frequency and microwave field amplitude.

Ionacoustic super rogue waves in ultracold neutral plasmas with nonthermal electrons
View Description Hide DescriptionThe ionacoustic rogue waves in ultracold neutral plasmas consisting of ion fluid and nonthermal electrons are reported. A reductive perturbation method is used to obtain a nonlinear Schrödinger equation for describing the system and the modulation instability of the ionacoustic wave is analyzed. The critical wave number kc , which indicates where the modulational instability sets in, has been determined. Moreover, the possible region for the ionacoustic rogue waves to exist is defined precisely. The effects of the nonthermal parameter β and the ions effective temperature ratio on the critical wave number kc are studied. It is found that there are two critical wave numbers in our plasma system. For low wave number, increasing β would lead to cringe kc until β approaches to its critical value , then further increase of β beyond would enhance the values of kc . For large wave numbers, the increase of β would lead to a decrease of kc . However, increasing would lead to the reduction of kc for all values of the wave number. The dependence of the rogue waves profile on the plasma parameters is numerically examined. It is found that the rogue wave amplitudes have complex behavior with increasing β. Furthermore, the enhancement of and the carrier wave number k reduces the rogue wave amplitude. It is noticed that near to the critical wave number, the rogue wave amplitude becomes high, but it shrinks whenever we stepped away from kc . The implications of our results in laboratory ultracold neutral plasma experiments are briefly discussed.

Twodimensional cylindrical ionacoustic solitary and rogue waves in ultrarelativistic plasmas
View Description Hide DescriptionThe propagation of ionacoustic (IA) solitary and rogue waves is investigated in a twodimensional ultrarelativistic degenerate warm dense plasma. By using the reductive perturbation technique, the cylindrical Kadomtsev–Petviashvili (KP) equation is derived, which can be further transformed into a Korteweg–de Vries (KdV) equation. The latter admits a solitary wave solution. However, when the frequency of the carrier wave is much smaller than the ion plasma frequency, the KdV equation can be transferred to a nonlinear Schrödinger equation to study the nonlinear evolution of modulationally unstable modified IA wavepackets. The propagation characteristics of the IA solitary and rogue waves are strongly influenced by the variation of different plasma parameters in an ultrarelativistic degenerate dense plasma. The present results might be helpful to understand the nonlinear electrostatic excitations in astrophysical degenerate dense plasmas.

Numerical magnetohydrodynamic simulations of expanding flux ropes: Influence of boundary driving
View Description Hide DescriptionThe expansion dynamics of a magnetized, currentcarrying plasma arch is studied by means of timedependent ideal MHD simulations. Initial conditions model the setup used in recent laboratory experiments that in turn simulate coronal loops [J. Tenfelde et al., Phys. Plasmas 19, 072513 (2012); E. V. Stenson and P. M. Bellan, Plasma Phys. Controlled Fusion 54, 124017 (2012)]. Boundary conditions of the electric field at the “lower” boundary, intersected by the arch, are chosen such that poloidal magnetic flux is injected into the domain, either localized at the arch footpoints themselves or halfway between them. These conditions are motivated by the tangential electric field expected to exist in the laboratory experiments due to the external circuit that drives the plasma current. The boundary driving is found to systematically enhance the expansion velocity of the plasma arch. While perturbations at the arch footpoints also deform its legs and create characteristic elongated segments, a perturbation between the footpoints tends to push the entire structure upwards, retaining an ellipsoidal shape.

Automation of the guiding center expansion
View Description Hide DescriptionWe report on the use of the recently developed Mathematica package VEST (Vector Einstein Summation Tools) to automatically derive the guiding center transformation. Our Mathematica code employs a recursive procedure to derive the transformation orderbyorder. This procedure has several novel features. (1) It is designed to allow the user to easily explore the guiding center transformation's numerous nonunique forms or representations. (2) The procedure proceeds entirely in cartesian position and velocity coordinates, thereby producing manifestly gyrogauge invariant results; the commonly used perpendicular unit vector fields are never even introduced. (3) It is easy to apply in the derivation of higherorder contributions to the guiding center transformation without fear of human error. Our code therefore stands as a useful tool for exploring subtle issues related to the physics of toroidal momentum conservation in tokamaks.

Shielding effect and wakefield pattern of a moving test charge in a nonMaxwellian dusty plasma
View Description Hide DescriptionBy using the VlasovPoisson equations, we calculate an expression for the electrostatic potential caused by a test charge in an unmagnetized nonMaxwellian dusty plasma, whose constituents are the superthermal hotelectrons, the mobile coldelectrons with a neutralizing background of cold ions, and charge fluctuating isolated dust grains. The superthermality effects due to hot electrons not only modify the dielectric constant of the electronacoustic waves but also significantly affect the electrostatic potential. The latter can be decomposed into the DebyeHückel and oscillatory wake potentials. Analytical and numerical results reveal that the DebyeHückel and wakefield potentials converge to the Maxwellian case for large values of superthermality parameter. Furthermore, the plasma parameters play a vital role in the formation of shielding and wakefield pattern in a twoelectron temperature plasma. The present results should be important for laboratory and space dusty plasmas, where hotelectrons can be assumed to follow the nonMaxwellian distribution function.

Neutrino oscillations in a turbulent plasma
View Description Hide DescriptionA new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both timeinvariant and timedependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicates the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.

Numerical study on a 0.4 THz second harmonic gyrotron with high power
View Description Hide DescriptionTerahertz and subterahertz science and technology are promising topics today. However, it is difficult to obtain high power source of terahertz wave. In this paper, the mode competition and beamwave interaction in a gradually tapered cavity are studied to achieve high efficiency of a 0.4THz second harmonic gyrotron in practice. In order to attain high power and stable radiation, the TE32,5 mode is selected as the operating mode of the desired gyrotron to realize single mode oscillation. The issues of studying on the highorder mode gyrotrons are solved effectively by transforming the generalized telegraphist's equations. The efficiency and output power of the gyrotron under different conditions have been calculated by the code, which is based on the transformed equations. Consequently, the results show that single mode second harmonic radiation with power of over 150 kW at frequency of 0.4 THz could be achieved.

The existence of electronacoustic shock waves and their interactions in a nonMaxwellian plasma with qnonextensive distributed electrons
View Description Hide DescriptionWe present a theoretical investigation for the nonlinear interaction between electronacoustic shock waves in a nonextensive twoelectron plasma. The interaction is governed by a pair of Kortewegde VriesBurgers equations. We focus on studying the colliding effects on the propagation of shock waves, more specifically, we have studied the effects of plasma parameters, i.e., the nonextensive parameter q, the “hot” to “cold” electron number density ratio α, and the normalized electron kinematic viscosity on the trajectory changes (phase shifts) of shock waves. It is found that there are trajectory changes (phase shifts) for both colliding shock waves in the present plasma system. We also noted that the nonlinearity has no decisive effect on the trajectory changes, the occurrence of trajectory changes may be due to the combined role played by the dispersion and dissipation of the nonlinear structure. Our theoretical study may be beneficial to understand the propagation and interaction of nonlinear electrostatic waves and may brings a possibility to develop the nonlinear theory of electronacoustic waves in astrophysical plasma systems.

Parameter spaces for linear and nonlinear whistlermode waves
View Description Hide DescriptionWe examine the growth of magnetospheric whistlermode waves which comprises a linear growth phase followed by a nonlinear growth phase. We construct timeprofiles for the wave amplitude that smoothly match at the transition between linear and nonlinear wave growth. This matching procedure can only take place over a limited “matching region” in space, where AT is the electron thermal anisotropy, Nh is the hot (energetic) electron number density, and N 0 is the cold (background) electron number density. We construct this matching region and determine how the matching wave amplitude varies throughout the region. Further, we specify a boundary in space that separates a region where only linear chorus wave growth can occur from the region in which fully nonlinear chorus growth is possible. We expect that this boundary should prove of practical use in performing computationally expensive fullscale particle simulations, and in interpreting experimental wave data.

Effects of higherorder Kerr nonlinearity and plasma diffraction on multiple filamentation of ultrashort laser pulses in air
View Description Hide DescriptionThe effect of higherorder Kerr nonlinearity on channel formation by, and filamentation of, ultrashort laser pulses propagating in air is considered. Filament patterns originating from multiphoton ionization of the air molecules with and without the higherorder Kerr and molecularrotation effects are investigated. It is found that diverging multiple filaments are formed if only the plasmainduced defocusing effect is included. In the presence of the higherorder Kerr effects, the light channel can exist for a long distance. The effect of noise on the filament patterns is also discussed.

Parametric coupling of lower hybrid wave with gyrating ion beam driven ion cyclotron instability in a plasma
View Description Hide DescriptionA lower hybrid wave, launched into a tokamak for supplementary heating in the presence of neutral beam turned gyrating ion beam, is seen to excite some prominent channels of parametric decay. The beam driven deuterium cyclotron mode is further destabilized by the lower hybrid pump through the nonlinear 4wave coupling, involving higher and lower frequency lower hybrid sidebands, when where is the lower hybrid frequency, and are the frequency and parallel wave number of the pump wave, and is the velocity of ion beam parallel to the magnetic field. The growth rate increases with parallel wave number of the ioncyclotron mode. The pump is also susceptible to parametric upconversion into an upper sideband shifted by the frequency of the negative energy deuterium cyclotron mode. For typical parameters, the growth rate of this channel is around one fiftieth of deuterium cyclotron frequency and falls off with the transverse wave number of the mode.

Nonlinear theory of intense laserplasma interactions modified by vacuum polarization effects
View Description Hide DescriptionThe classical nonlinear theory of laserplasma interactions is corrected by taking account of the vacuum polarization effects. A set of wave equations are obtained by using the HeisenbergEuler Lagrangian density and the derivative correction with the firstorder quantum electrodynamic effects. A model more suitable to formulate the interactions of ultrastrong lasers and highenergydensity plasmas is developed. In the result, some environments in which the effects of vacuum polarization will be enhanced are discussed.

Statistical and spectral properties of magnetic islands in reconnecting current sheets during tworibbon flares
View Description Hide DescriptionWe perform a set of two dimensional resistive magnetohydrodynamic simulations to study the reconnection process occurring in current sheets that develop during solar eruptions. Reconnection commences gradually and produces smallscale structures inside the current sheet, which has one end anchored to the bottom boundary and the other end open. The main features we study include plasmoids (or plasma blobs) flowing in the sheet, and Xpoints between pairs of adjacent islands. The statistical properties of the fine structure and the dependence of the spectral energy on these properties are examined. The flux and size distribution functions of plasmoids roughly follow inverse square power laws at large scales. The mass distribution function is steep at large scales and shallow at small scales. The size distribution also shows that plasmoids are highly asymmetric soon after being formed, while older plasmoids tend to be more circular. The spectral profiles of magnetic and kinetic energy inside the current sheet are both consistent with a power law. The corresponding spectral indices γ are found to vary with the magnetic Reynolds number of the system, but tend to approach a constant for large . The motion and growth of blobs change the spectral index. The growth of new islands causes the power spectrum to steepen, but it becomes shallower when old and large plasmoids leave the computational domain.

A primitive kineticfluid model for quasiparallel propagating magnetohydrodynamic waves
View Description Hide DescriptionThe extension and limitation of the existing onedimensional kineticfluid model (VlasovMHD (magnetohydrodynamic) model), which has been used to analyze parametric instabilities of parallel propagating Alfvén waves, are discussed. The inconsistency among the given velocity distribution functions in the past studies is resolved through the systematic derivation of the multidimensional VlasovMHD model. The linear dispersion analysis of the present model indicates that the collisionless damping of the slow modes is adequately evaluated in low beta plasmas, although the deviation between the present model and the fullVlasov theory increases with increasing plasma beta and increasing propagation angle. This is because the transittime damping is not correctly evaluated in the present model. It is also shown that the ponderomotive density fluctuations associated with the envelopemodulated quasiparallel propagating Alfvén waves derived from the present model is not consistent with those derived from the other models such as the Landaufluid model, except for low beta plasmas. The result indicates the present model would be useful to understand the linear and nonlinear development of the Alfvénic turbulence in the inner heliosphere, whose condition is relatively low beta, while the existing model and the present model are insufficient to discuss the parametric instabilities of Alfvén waves in high beta plasmas and the obliquely propagating waves.

Modulational interactions in quantum plasmas
View Description Hide DescriptionA formalism for treating modulational interactions of electrostatic fields in collisionless quantum plasmas is developed, based on the kinetic WignerPoisson model of quantum plasma. This formalism can be used in a range of problems of nonlinear interaction between electrostatic fields in a quantum plasma, such as development of turbulence, selforganization, as well as transition from the weak turbulent state to strong turbulence. In particular, using this formalism, we obtain the kinetic quantum Zakharov equations that describe nonlinear coupling of high frequency Langmuir waves to low frequency plasma density variations, for cases of nondegenerate and degenerate plasma electrons.