Physics of Plasmas is dedicated to the publication of original experimental and theoretical contributions in plasma physics. Physics of Plasmas is published by AIP Publishing with the cooperation of the APS Division of Plasma Physics.
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Differentially rotating flows of unmagnetized, highly conducting plasmas have been created in the Plasma Couette Experiment. Previously, hotcathodes have been used to control plasma rotation by a stirring technique [C. Collins et al., Phys. Rev. Lett. 108, 115001 (2012)] on the outer cylindrical boundary—these plasmas were nearly rigid rotors, modified only by the presence of a neutral particle drag. Experiments have now been extended to include stirring from an inner boundary, allowing for generalized circular Couette flow and opening a path for both hydrodynamic and magnetohydrodynamic experiments, as well as fundamental studies of plasma viscosity. Plasma is confined in a cylindrical, axisymmetric, multicusp magnetic field, with Te < 10 eV, Ti < 1 eV, and . Azimuthal flows (up to 12 km/s, M = V∕cs ∼ 0.7) are driven by edge J × B torques in helium, neon, argon, and xenon plasmas, and the experiment has already achieved Rm ∼ 65 and . We present measurements of a selfconsistent, rotationinduced, speciesdependent radial electric field, which acts together with pressure gradient to provide the centripetal acceleration for the ions. The maximum flow speeds scale with the Alfvén critical ionization velocity, which occurs in partially ionized plasma. A hydrodynamic stability analysis in the context of the experimental geometry and achievable parameters is also explored.

In this research, a series of singlemode, indirectdrive, ablative RayleighTaylor (RT) instability experiments performed on the ShenguangII laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007)] using planar target is reported. The simulation results from the onedimensional hydrocode for the planar foil trajectory experiment indicate that the energy flux at the hohlraum wall is obviously less than that at the laser entrance hole. Furthermore, the nonPlanckian spectra of xray source can strikingly affect the dynamics of the foil flight and the perturbation growth. Clear images recorded by an xray framing camera for the RT growth initiated by small and largeamplitude perturbations are obtained. The observed onset of harmonic generation and transition from linear to nonlinear growth regime is well predicted by twodimensional hydrocode simulations.

By considering particle, momentum, and energy balance equations, we develop a semiempirical quasi onedimensional analytical discharge model of radiofrequency and helicon plasma thrusters. The model, which includes both the upstream plasma source region as well as the downstream diverging magnetic nozzle region, is compared with experimental measurements and confirms current performance levels. Analysis of the discharge model identifies plasma power losses on the radial and back wall of the thruster as the major performance reduction factors. These losses serve as sinks for the input power which do not contribute to the thrust, and which reduce the maximum plasma density and hence propellant utilization. With significant radial plasma losses eliminated, the discharge model (with argon) predicts specific impulses in excess of 3000 s, propellant utilizations above 90%, and thruster efficiencies of about 30%.

Two magnetic flux ropes that collide and bounce have been characterized in the laboratory. We find screw pinch profiles that include ion flow , magnetic field , current density , and plasma pressure. The electron flow can be inferred, allowing the evaluation of the Hall term in a two fluid magnetohydrodynamic Ohm's Law. Flux ropes that are initially cylindrical are mutually attracted and compress each other, which distorts the cylindrical symmetry. Magnetic field is created via the induction term in Ohm's Law where inplane (perpendicular) shear of parallel flow (along the flux rope) is the dominant feature, along with some dissipation and magnetic reconnection. We predict and measure the growth of a quadrupole outofplane magnetic field δBz . This is a simple and coherent example of a shear flow driven dynamo. There is some similarity with two dimensional reconnection scenarios, which induce a current sheet and thus outofplane flow in the third dimension, despite the customary picture that considers flows only in the reconnection plane. These data illustrate a general and deterministic mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence.

Using 2D Molecular Dynamics simulation, the equilibrium and dynamical properties of a gravitationally equilibrated Yukawa liquid are investigated. We observe that due to asymmetry introduced in one direction by gravity, several interesting features arise. For example, for a given value of coupling parameter Γ, screening parameter κ, and according to a chosen value of gravitational force g (say in ydirection), the system is seen to exhibit super, sub or normal diffusion. Interestingly, xaveraged density profiles, unlike a barotropic fluid, acquires sharp, free surface with scale free linear ydependence. As can be expected for a system with macroscopic gradients, selfdiffusion calculated from GreenKubo’s formalism does not agree with that obtained from EinsteinSmoluchowski diffusion. A 2D angularradial pair correlation function g(r, θ) clearly indicates asymmetric features induced by gravity. We observe that due to compression in ydirection, though in liquid state for all values of gravity considered, the transverse mode is found to predominant as compared to the longitudinal mode, leading to a novel Anisotropic Solidlike Yukawa liquid.