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Mar 2013

Volume 20, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 20, 032106 (2013); http://dx.doi.org/10.1063/1.4794320 (10 pages)

M. Raghunathan and R. Ganesh
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back to top Nonlinear Phenomena, Turbulence, Transport

Propagation of ion-acoustic solitons in an electron beam-superthermal plasma system with finite ion-temperature: Linear and fully nonlinear investigation

E. Saberian, A. Esfandyari-Kalejahi, A. Rastkar-Ebrahimzadeh, and M. Afsari-Ghazi

Phys. Plasmas 20, 032307 (2013); http://dx.doi.org/10.1063/1.4795745 (15 pages)

Online Publication Date: 19 March 2013

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The propagation of ion-acoustic (IA) solitons is studied in a plasma system, comprised of warm ions and superthermal (Kappa distributed) electrons in the presence of an electron-beam by using a hydrodynamic model. In the linear analysis, it is seen that increasing the superthermality lowers the phase speed of the IA waves. On the other hand, in a fully nonlinear investigation, the Mach number range and characteristics of IA solitons are analyzed, parametrically and numerically. It is found that the accessible region for the existence of IA solitons reduces with increasing the superthermality. However, IA solitons with both negative and positive polarities can coexist in the system. Additionally, solitary waves with both subsonic and supersonic speeds are predicted in the plasma, depending on the value of ion-temperature and the superthermality of electrons in the system. It is examined that there are upper critical values for beam parameters (i.e., density and velocity) after which, IA solitary waves could not propagate in the plasma. Furthermore, a typical interaction between IA waves and the electron-beam in the plasma is confirmed.
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52.35.Sb Solitons; BGK modes
52.40.Mj Particle beam interactions in plasmas
02.60.-x Numerical approximation and analysis
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Nonlinear interaction and parametric instability of kinetic Alfvén waves in multicomponent plasmas

J. S. Zhao, D. J. Wu, L. Yang, and J. Y. Lu

Phys. Plasmas 20, 032308 (2013); http://dx.doi.org/10.1063/1.4796054 (6 pages)

Online Publication Date: 21 March 2013

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Nonlinear couplings among kinetic Alfvén waves are investigated for a three-component plasma consisting of electrons, protons, and heavy ions. The parametric instability is investigated, and the growth rate is obtained. In the kinetic regime, the growth rate for the parallel decay instability increases with the heavy ion content, but the growth rate for the reverse decay is independent of the latter since the perpendicular wavelength is much larger than the ion gyroradius. It decreases with the heavy ion content when the perpendicular wavelength is of the order of the ion gyroradius. It is also found that in the short perpendicular wavelength limit, the growth rate is only weakly affected by the heavy ions. On the other hand, in the inertial regime, for both parallel and reverse decay cases, the growth rate decreases as the number of heavy ions becomes large.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Verification of electromagnetic fluid-kinetic hybrid electron model in global gyrokinetic particle simulation

I. Holod and Z. Lin

Phys. Plasmas 20, 032309 (2013); http://dx.doi.org/10.1063/1.4798392 (6 pages)

Online Publication Date: 26 March 2013

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The fluid-kinetic hybrid electron model is verified in global gyrokinetic particle simulation of linear electromagnetic drift-Alfvénic instabilities in tokamak. In particular, we have recovered the β-stabilization of the ion temperature gradient mode, transition to collisionless trapped electron mode, and the onset of kinetic ballooning mode as βe (ratio of electron kinetic pressure to magnetic pressure) increases.
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52.55.Fa Tokamaks, spherical tokamaks
52.65.Ww Hybrid methods
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Impurity transport in trapped electron mode driven turbulence

A. Mollén, I. Pusztai, T. Fülöp, and S. Moradi

Phys. Plasmas 20, 032310 (2013); http://dx.doi.org/10.1063/1.4796196 (13 pages)

Online Publication Date: 28 March 2013

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Trapped electron mode turbulence is studied by gyrokinetic simulations with the GYRO code and an analytical model including the effect of a poloidally varying electrostatic potential. Its impact on radial transport of high-Z trace impurities close to the core is thoroughly investigated, and the dependence of the zero-flux impurity density gradient (peaking factor) on local plasma parameters is presented. Parameters such as ion-to-electron temperature ratio, electron temperature gradient, and main species density gradient mainly affect the impurity peaking through their impact on mode characteristics. The poloidal asymmetry, the safety factor, and magnetic shear have the strongest effect on impurity peaking, and it is shown that under certain scenarios where trapped electron modes are dominant, core accumulation of high-Z impurities can be avoided. We demonstrate that accounting for the momentum conservation property of the impurity-impurity collision operator can be important for an accurate evaluation of the impurity peaking factor.
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52.35.Ra Plasma turbulence
52.25.Vy Impurities in plasmas
52.65.Tt Gyrofluid and gyrokinetic simulations
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Xz Magnetized plasmas
back to top Magnetically Confined Plasmas, Heating, Confinement

Collisional damping of the geodesic acoustic mode

Zhe Gao

Phys. Plasmas 20, 032501 (2013); http://dx.doi.org/10.1063/1.4794339 (4 pages) | Cited 1 time

Online Publication Date: 1 March 2013

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The frequency and damping rate of the geodesic acoustic mode (GAM) is revisited by using a gyrokinetic model with a number-conserving Krook collision operator. It is found that the damping rate of the GAM is non-monotonic as the collision rate increases. At low ion collision rate, the damping rate increases linearly with the collision rate; while as the ion collision rate is higher than vti/R, where vti and R are the ion thermal velocity and major radius, the damping rate decays with an increasing collision rate. At the same time, as the collision rate increases, the GAM frequency decreases from the (7/4+τ)vti/R to (1+τ)vti/R, where τ is the ratio of electron temperature to ion temperature.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Fast wave stabilization/destabilization of drift waves in a plasma

Pawan Kumar and V. K. Tripathi

Phys. Plasmas 20, 032502 (2013); http://dx.doi.org/10.1063/1.4794341 (5 pages)

Online Publication Date: 1 March 2013

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Four wave-nonlinear coupling of a large amplitude whistler with low frequency drift wave and whistler wave sidebands is examined. The pump and whistler sidebands exert a low frequency ponderomotive force on electrons introducing a frequency shift in the drift wave. For whistler pump propagating along the ambient magnetic field Bsmath with wave number math0, drift waves of wave number math = math⊥+k||math see an upward frequency shift when k⊥2/k02>4k||/k0 and are stabilized once the whistler power exceeds a threshold value. The drift waves of low transverse wavelength tend to be destabilized by the nonlinear coupling. Oblique propagating whistler pump with transverse wave vector parallel to math⊥ is also effective but with reduced effectiveness.
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52.35.Kt Drift waves
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

The effect of emissive biased limiter on the magnetohydrodynamic modes in the IR-T1 tokamak

M. Ghasemloo, M. Ghoranneviss, M. K. Salem, R. Arvin, S. Mohammadi, and A. Nik Mohammadi

Phys. Plasmas 20, 032503 (2013); http://dx.doi.org/10.1063/1.4791658 (7 pages)

Online Publication Date: 1 March 2013

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A moveable emissive biased limiter (EBL) for the investigation of spatial and temporal structure of MHD modes in IR-T1 tokamak, based on mirnov oscillations, was designed and constructed. The biasing has been considered to improve the global confinement by setting up an electric field at the plasma edge. Radial electric field (Er) modifies edge plasma turbulence, plasma rotation, and transport. Mirnov oscillations using singular value decomposition (SVD) and wavelet techniques were analyzed. SVD algorithm has been employed to analyze the frequency and wavenumber harmonics of the MHD fluctuations. The time-resolved frequency component analysis has been performed using wavelets. The EBL was applied to plasma at 10 ms with negative polarity. The results show that after applying EBL, the m = 2 mode is grown, m = 3 mode is suppressed, and Hα radiation is decreased. Furthermore, results of the wavelet analysis of mirnov coil in the time range of 8–12 ms indicate that 1.5 ms after applying EBL, the MHD frequency is reduced from 45 kHz to 25 kHz.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties

On the formation of m = 1, n = 1 density snakes

Linda E. Sugiyama

Phys. Plasmas 20, 032504 (2013); http://dx.doi.org/10.1063/1.4793450 (11 pages) | Cited 1 time

Online Publication Date: 4 March 2013

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The m/n = 1/1 helical ion density “snake” located near the q = 1 magnetic surface in a toroidal, magnetically confined plasma arises naturally in resistive MHD, when the plasma density evolves separately from pressure. Nonlinear numerical simulations show that a helical density perturbation applied around q = 1 can form a quasi-steady state over q≳1 with math of opposite average sign to math. Two principal outcomes depend on the magnitude of math/n and the underlying stability of the 1/1 internal kink mode. For a small q<1 central region, a moderate helical density drives a new, slowly growing type of nonlinear 1/1 internal kink inside q<1, with small math and ∇math ≃ ∇(nmath). The hot kink core moves away from, or perpendicular to, the high density region near q ≃ 1, preserving the snake density during a sawtooth crash. The mode resembles the early stage of heavy-impurity-ion snakes in ohmic discharges, including recent observations in Alcator C-Mod. For a larger, more unstable q<1 region, the helical density perturbation drives a conventional 1/1 kink where math aligns with math, leading to a rapid sawtooth crash. The crash redistributes the density to a localized helical concentration inside q≲1, similar to experimentally observed snakes that are initiated by a sawtooth crash.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Vy Impurities in plasmas

Thermal ion effects on kinetic beta-induced Alfvén eigenmodes excited by energetic ions

Longyu Qi, J. Q. Dong, A. Bierwage, Gaimin Lu, and Z. M. Sheng

Phys. Plasmas 20, 032505 (2013); http://dx.doi.org/10.1063/1.4794287 (12 pages)

Online Publication Date: 7 March 2013

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Kinetic beta-induced Alfvén eigenmodes (KBAEs) driven by energetic ions are numerically investigated using revised AWECS code. The thermal ion density and temperature gradients are taken into account. It is found that the growth rate of the KBAEs increases with the thermal ion pressure gradient, and the contributions from the density gradient and temperature gradient of the thermal ions to the enhancement of the instability are comparable. The damping effect of thermal ion dynamics on the modes is also observed.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Kj Magnetohydrodynamic and fluid equation
52.65.Tt Gyrofluid and gyrokinetic simulations
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties

Physics basis of Multi-Mode anomalous transport module

T. Rafiq, A. H. Kritz, J. Weiland, A. Y. Pankin, and L. Luo

Phys. Plasmas 20, 032506 (2013); http://dx.doi.org/10.1063/1.4794288 (13 pages) | Cited 1 time

Online Publication Date: 7 March 2013

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The derivation of Multi-Mode anomalous transport module version 8.1 (MMM8.1) is presented. The MMM8.1 module is advanced, relative to MMM7.1, by the inclusion of peeling modes, dependence of turbulence correlation length on flow shear, electromagnetic effects in the toroidal momentum diffusivity, and the option to compute poloidal momentum diffusivity. The MMM8.1 model includes a model for ion temperature gradient, trapped electron, kinetic ballooning, peeling, collisionless and collision dominated magnetohydrodynamics modes as well as model for electron temperature gradient modes, and a model for drift resistive inertial ballooning modes. In the derivation of the MMM8.1 module, effects of collisions, fast ion and impurity dilution, non-circular flux surfaces, finite beta, and Shafranov shift are included. The MMM8.1 is used to compute thermal, particle, toroidal, and poloidal angular momentum transports. The fluid approach which underlies the derivation of MMM8.1 is expected to reliably predict, on an energy transport time scale, the evolution of temperature, density, and momentum profiles in plasma discharges for a wide range of plasma conditions.
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52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks

Nonideal fishbone instability excited by trapped energetic electrons

Y. Liu (刘宇), Z. T. Wang (王中天), Y. X. Long (龙永兴), J. Q. Dong (董家 齐), and C. J. Tang (唐昌建)

Phys. Plasmas 20, 032507 (2013); http://dx.doi.org/10.1063/1.4794738 (5 pages)

Online Publication Date: 7 March 2013

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It is shown that trapped energetic electrons can resonate with the collisionless m = 1 nonideal kink mode, therefore exciting the nonideal e-fishbone, which would often lead to a drop in soft x-ray emissivity and frequency chirping. The theory predictions agree well with the experimental observations of e-fishbone on HL-2A. It is also found that the effects of MHD energy of background plasma might be the reason for the observed phenomena: frequency chirping up and down, and V-font-style sweeping.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.55.Tn Ideal and resistive MHD modes; kinetic modes

The excitation of geodesic acoustic mode flows by a resonant magnetic field and by resonant heating

Robert G. Kleva and A. B. Hassam

Phys. Plasmas 20, 032508 (2013); http://dx.doi.org/10.1063/1.4794837 (6 pages)

Online Publication Date: 12 March 2013

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Toroidal magnetohydrodynamic (MHD) simulations demonstrate that sheared poloidal flows in tokamaks can be generated by the resonant excitation of the geodesic acoustic mode (GAM). Poloidal flows are generated by two resonant excitation methods: oscillating currents in an external coil and an oscillating heat source. The coil current and the heat source oscillate in time at the local GAM frequency. The sheared poloidal flow generated by the excitation of the GAM may be useful for the suppression of plasma instabilities.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.50.Dg Plasma sources

The infinite interface limit of multiple-region relaxed magnetohydrodynamics

G. R. Dennis, S. R. Hudson, R. L. Dewar, and M. J. Hole

Phys. Plasmas 20, 032509 (2013); http://dx.doi.org/10.1063/1.4795739 (6 pages)

Online Publication Date: 15 March 2013

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We show the stepped-pressure equilibria that are obtained from a generalization of Taylor relaxation known as multi-region, relaxed magnetohydrodynamics (MRXMHD) are also generalizations of ideal magnetohydrodynamics (ideal MHD). We show this by proving that as the number of plasma regions becomes infinite, MRXMHD reduces to ideal MHD. Numerical convergence studies illustrating this limit are presented.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
02.60.-x Numerical approximation and analysis

Investigation of the transport shortfall in Alcator C-Mod L-mode plasmas

N. T. Howard, A. E. White, M. Greenwald, M. L. Reinke, J. Walk, C. Holland, J. Candy, and T. Görler

Phys. Plasmas 20, 032510 (2013); http://dx.doi.org/10.1063/1.4795301 (5 pages) | Cited 1 time

Online Publication Date: 18 March 2013

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A so-called “transport shortfall,” where ion and electron heat fluxes and turbulence are underpredicted by gyrokinetic codes, has been robustly identified in DIII-D L-mode plasmas for ρ>0.55 [T. L. Rhodes et al., Nucl. Fusion 51(6), 063022 (2011); and C. Holland et al., Phys. Plasmas 16(5), 052301 (2009)]. To probe the existence of a transport shortfall across different tokamaks, a dedicated scan of auxiliary heated L-mode discharges in Alcator C-Mod are studied in detail with nonlinear gyrokinetic simulations for the first time. Two discharges, only differing by the amount of auxiliary heating are investigated using both linear and nonlinear simulation of the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)]. Nonlinear gyrokinetic simulation of the low and high input power discharges reveals a discrepancy between simulation and experiment in only the electron heat flux channel of the low input power discharge. However, both discharges demonstrate excellent agreement in the ion heat flux channel, and the high input power discharge demonstrates simultaneous agreement with experiment in both the electron and ion heat flux channels. A summary of linear and nonlinear gyrokinetic results and a discussion of possible explanations for the agreement/disagreement in each heat flux channel is presented.
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52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.65.Tt Gyrofluid and gyrokinetic simulations
52.80.-s Electric discharges

Effect of magnetic fluctuations on the confinement and dynamics of runaway electrons in the HT-7 tokamak

R. J. Zhou, L. Q. Hu, E. Z. Li, M. Xu, G. Q. Zhong, L. Q. Xu, and S. Y. Lin

Phys. Plasmas 20, 032511 (2013); http://dx.doi.org/10.1063/1.4795740 (8 pages)

Online Publication Date: 18 March 2013

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The nature of runaway electrons is such that the confinement and dynamics of the electrons can be strongly affected by magnetic fluctuations in plasma. Experimental results in the HT-7 tokamak indicated significant losses of runaway electrons due to magnetic fluctuations, but the loss processes did not only rely on the fluctuation amplitude. Efficient radial runaway transport required that there were no more than small regions of the plasma volume in which there was very low transport of runaways. A radial runaway diffusion coefficient of Dr ≈ 10 m2s-1 was derived for the loss processes, and diffusion coefficient near the resonant magnetic surfaces and shielding factor ϒ = 0.8 were deduced. Test particle equations were used to analyze the effect of magnetic fluctuations on runaway dynamics. It was found that the maximum energy that runaways can gain is very sensitive to the value of αs (i.e., the fraction of plasma volume with reduced transport). αs = (0.28−0.33) was found for the loss processes in the experiment, and maximum runaway energy could be controlled in the range of E = (4 MeV-6 MeV) in this case. Additionally, to control the maximum runaway energy below 5 MeV, the normalized electric field needed to be under a critical value Dα = 6.8, and the amplitude normalized magnetic fluctuations math needed to be at least of the order of math ≈ 3×10−5.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

Effects of magnetic field on anisotropic temperature relaxation

Chao Dong, Haijun Ren, Huishan Cai, and Ding Li

Phys. Plasmas 20, 032512 (2013); http://dx.doi.org/10.1063/1.4795728 (11 pages)

Online Publication Date: 19 March 2013

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In a strongly magnetized plasma, where the particles' thermal gyro-radii are smaller than the Debye length, the magnetic field greatly affects the plasma's relaxation processes. The expressions for the time rates of change of the electron and ion parallel and perpendicular temperatures are obtained and calculated analytically for small anisotropies through considering binary collisions between charged particles in the presence of a uniform magnetic field by using perturbation theory. Based on these expressions, the effects of the magnetic field on the relaxation of anisotropic electron and ion temperatures due to electron-electron collisions, ion-ion collisions, and electron-ion collisions are investigated. Consequently, the relaxation times of anisotropic electron and ion temperatures to isotropy are calculated. It is shown that electron-ion collisions can affect the relaxation of an anisotropic ion distribution in the strong magnetic field.
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52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties
52.25.Xz Magnetized plasmas

Traveling wave current drive theory for an arbitrary m-polar configuration

V. N. Duarte, R. A. Clemente, and R. Farengo

Phys. Plasmas 20, 032513 (2013); http://dx.doi.org/10.1063/1.4796089 (10 pages)

Online Publication Date: 21 March 2013

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An extension of the formalism employed to describe current drive in magnetized plasmas by means of traveling magnetic fields (or double-helix configuration) is presented. In all previous theoretical studies, only driving fields with dipolar topology have been employed and the figure of merit of the current drive mechanism has never been analyzed in terms of the dissipation in the power feeding circuit. In this paper, we show how to express the model equations in terms of the current amplitude in the coils, for an arbitrary number of equally spaced coils wound around the plasma column. We present a brief review of the existing theory and a theoretical formulation, valid for an arbitrary m-polar helical symmetry, which removes the above mentioned complications and limitations. In the limit of straight coils, our magnetic field expression agrees exactly with well-established results of the literature for rotating magnetic field current drive. Finally, we present initial numerical results from a recently developed code which consistently compares the steady driven nonlinear Hall currents and steady fields, corresponding to different configurations in terms of the Ohmic dissipation in the helical coils and discuss future perspectives.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Xz Magnetized plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
back to top Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

Mixing of equations of state for xenon-deuterium using density functional theory

Rudolph J. Magyar and Thomas R. Mattsson

Phys. Plasmas 20, 032701 (2013); http://dx.doi.org/10.1063/1.4793441 (6 pages)

Online Publication Date: 1 March 2013

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We report on a theoretical study of equation of state (EOS) properties of fluid and dense plasma mixtures of xenon and deuterium to explore and illustrate the basic physics of the mixing of a light element with a heavy element. Accurate EOS models are crucial to achieve high-fidelity hydrodynamics simulations of many high-energy-density phenomena, for example inertial confinement fusion and strong shock waves. While the EOS is often tabulated for separate species, the equation of state for arbitrary mixtures is generally not available, requiring properties of the mixture to be approximated by combining physical properties of the pure systems. Density functional theory (DFT) at elevated-temperature is used to assess the thermodynamics of the xenon-deuterium mixture at different mass ratios. The DFT simulations are unbiased as to elemental species and therefore provide comparable accuracy when describing total energies, pressures, and other physical properties of mixtures as they do for pure systems. The study focuses on addressing the accuracy of different mixing rules in the temperature range 1000–40 000 K for pressures between 100 and 600 GPa (1–6 Mbar), thus, including the challenging warm dense matter regime of the phase diagram. We find that a mix rule taking into account pressure equilibration between the two species performs very well over the investigated range.
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52.25.Kn Thermodynamics of plasmas
52.35.Tc Shock waves and discontinuities
31.15.E- Density-functional theory
28.52.-s Fusion reactors
51.30.+i Thermodynamic properties, equations of state

Experimental investigation of the ribbon-array ablation process

Zhenghong Li, Rongkun Xu, Yanyun Chu, Jianlun Yang, Zeping Xu, Ning Ding, Fan Ye, Faxin Chen, Feibiao Xue, Jiamin Ning, Yi Qin, Shijian Meng, Qingyuan Hu, Fenni Si, Jinghua Feng, et al.

Phys. Plasmas 20, 032702 (2013); http://dx.doi.org/10.1063/1.4794199 (6 pages)

Online Publication Date: 4 March 2013

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Ablation processes of ribbon-array loads, as well as wire-array loads for comparison, were investigated on Qiangguang-1 accelerator. The ultraviolet framing images indicate that the ribbon-array loads have stable passages of currents, which produce axially uniform ablated plasma. The end-on x-ray framing camera observed the azimuthally modulated distribution of the early ablated ribbon-array plasma and the shrink process of the x-ray radiation region. Magnetic probes measured the total and precursor currents of ribbon-array and wire-array loads, and there exists no evident difference between the precursor currents of the two types of loads. The proportion of the precursor current to the total current is 15% to 20%, and the start time of the precursor current is about 25 ns later than that of the total current. The melting time of the load material is about 16 ns, when the inward drift velocity of the ablated plasma is taken to be 1.5 × 107 cm/s.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.La X-ray and γ-ray measurements
52.50.-b Plasma production and heating
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.70.Ds Electric and magnetic measurements

Magnetic field advection in two interpenetrating plasma streams

D. D. Ryutov, N. L. Kugland, M. C. Levy, C. Plechaty, J. S. Ross, and H. S. Park

Phys. Plasmas 20, 032703 (2013); http://dx.doi.org/10.1063/1.4794200 (10 pages) | Cited 1 time

Online Publication Date: 6 March 2013

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Laser-generated colliding plasma streams can serve as a test-bed for the study of various astrophysical phenomena and the general physics of self-organization. For streams of a sufficiently high kinetic energy, collisions between the ions of one stream with the ions of the other stream are negligible, and the streams can penetrate through each other. On the other hand, the intra-stream collisions for high-Mach-number flows can still be very frequent, so that each stream can be described hydrodynamically. This paper presents an analytical study of the effects that these interpenetrating streams have on large-scale magnetic fields either introduced by external coils or generated in the plasma near the laser targets. Specifically, a problem of the frozen-in constraint is assessed and paradoxical features of the field advection in this system are revealed. A possibility of using this system for studies of magnetic reconnection is mentioned.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Mj Particle beam interactions in plasmas
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Hydrodynamic simulations of long-scale-length two-plasmon–decay experiments at the Omega Laser Facility

S. X. Hu (胡素兴), D. T. Michel, D. H. Edgell, D. H. Froula, R. K. Follett, V. N. Goncharov, J. F. Myatt, S. Skupsky, and B. Yaakobi

Phys. Plasmas 20, 032704 (2013); http://dx.doi.org/10.1063/1.4794285 (10 pages) | Cited 1 time

Online Publication Date: 7 March 2013

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Direct-drive–ignition designs with plastic CH ablators create plasmas of long density scale lengths (Ln ≥ 500 μm) at the quarter-critical density (Nqc) region of the driving laser. The two-plasmon–decay (TPD) instability can exceed its threshold in such long-scale-length plasmas (LSPs). To investigate the scaling of TPD-induced hot electrons to laser intensity and plasma conditions, a series of planar experiments have been conducted at the Omega Laser Facility with 2-ns square pulses at the maximum laser energies available on OMEGA and OMEGA EP. Radiation–hydrodynamic simulations have been performed for these LSP experiments using the two-dimensional hydrocode draco. The simulated hydrodynamic evolution of such long-scale-length plasmas has been validated with the time-resolved full-aperture backscattering and Thomson-scattering measurements. draco simulations for CH ablator indicate that (1) ignition-relevant long-scale-length plasmas of Ln approaching ∼400 μm have been created; (2) the density scale length at Nqc scales as Ln(μm) ≃ (RDPP×I1/4/2); and (3) the electron temperature Te at Nqc scales as Te(keV) ≃ 0.95×math, with the incident intensity (I) measured in 1014 W/cm2 for plasmas created on both OMEGA and OMEGA EP configurations with different-sized (RDPP) distributed phase plates. These intensity scalings are in good agreement with the self-similar model predictions. The measured conversion fraction of laser energy into hot electrons fhot is found to have a similar behavior for both configurations: a rapid growth [fhot ≃ fc×(Gc/4)6 for Gc < 4] followed by a saturation of the form, fhot ≃ fc×(Gc/4)1.2 for Gc ≥ 4, with the common wave gain is defined as Gc = 3 × 10−2×IqcLnλ0/Te, where the laser intensity contributing to common-wave gain Iqc, Ln, Te at Nqc, and the laser wavelength λ0 are, respectively, measured in [1014 W/cm2], [μm], [keV], and [μm]. The saturation level fc is observed to be fc ≃ 10–2 at around Gc ≃ 4. The hot-electron temperature scales roughly linear with Gc. Furthermore, to mitigate TPD instability in long-scale-length plasmas, different ablator materials such as saran and aluminum have been investigated on OMEGA EP. Hot-electron generation has been reduced by a factor of 3–10 for saran and aluminum plasmas, compared to the CH case at the same incident laser intensity. draco simulations suggest that saran might be a better ablator for direct-drive–ignition designs as it balances TPD mitigation with an acceptable hydro-efficiency.
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52.65.Kj Magnetohydrodynamic and fluid equation
28.52.Cx Fueling, heating and ignition
52.25.Kn Thermodynamics of plasmas
52.40.Mj Particle beam interactions in plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)

Determination of the inductance of imploding wire array Z-pinches using measurements of load voltage

G. C. Burdiak, S. V. Lebedev, G. N. Hall, A. J. Harvey-Thompson, F. Suzuki-Vidal, G. F. Swadling, E. Khoory, L. Pickworth, S. N. Bland, P. de Grouchy, and J. Skidmore

Phys. Plasmas 20, 032705 (2013); http://dx.doi.org/10.1063/1.4794957 (8 pages)

Online Publication Date: 12 March 2013

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The inductance of imploding cylindrical wire array z-pinches has been determined from measurements of load voltage and current. A thorough analysis method is presented that explains how the load voltage of interest is found from raw signals obtained using a resistive voltage divider. This method is applied to voltage data obtained during z-pinch experiments carried out on the MAGPIE facility (1.4 MA, 240 ns rise-time) in order to calculate the load inductance and thereafter the radial trajectory of the effective current sheath during the snowplough implosion. Voltage and current are monitored very close to the load, allowing these calculations to be carried out without the need for circuit modelling. Measurements give a convergence ratio for the current of between 3.1 and 5.7 at stagnation of the pinch.
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52.59.Qy Wire array Z-pinches
52.40.Kh Plasma sheaths
52.80.Qj Explosions; exploding wires
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties

Ideal hydrodynamic scaling relations for a stagnated imploding spherical plasma liner formed by an array of merging plasma jets

J. T. Cassibry, M. Stanic, and S. C. Hsu

Phys. Plasmas 20, 032706 (2013); http://dx.doi.org/10.1063/1.4795732 (11 pages)

Online Publication Date: 18 March 2013

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This work presents scaling relations for the peak thermal pressure and stagnation time (over which peak pressure is sustained) for an imploding spherical plasma liner formed by an array of merging plasma jets. Results were derived from three-dimensional (3D) ideal hydrodynamic simulation results obtained using the smoothed particle hydrodynamics code SPHC. The 3D results were compared to equivalent one-dimensional (1D) simulation results. It is found that peak thermal pressure scales linearly with the number of jets and initial jet density and Mach number, quadratically with initial jet radius and velocity, and inversely with the initial jet length and the square of the chamber wall radius. The stagnation time scales approximately as the initial jet length divided by the initial jet velocity. Differences between the 3D and 1D results are attributed to the inclusion of thermal transport, ionization, and perfect symmetry in the 1D simulations. A subset of the results reported here formed the initial design basis for the Plasma Liner Experiment [S. C. Hsu et al., Phys. Plasmas 19, 123514 (2012)].
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52.75.-d Plasma devices
52.80.Qj Explosions; exploding wires
52.25.-b Plasma properties
52.25.Fi Transport properties
52.58.-c Other confinement methods
52.65.-y Plasma simulation
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“Bloch wave” modification of stimulated Raman by stimulated Brillouin scattering

E. S. Dodd, H. X. Vu, D. F. DuBois, and B. Bezzerides

Phys. Plasmas 20, 032707 (2013); http://dx.doi.org/10.1063/1.4796044 (11 pages)

Online Publication Date: 21 March 2013

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Using the reduced-description particle-in-cell (RPIC) method, we study the coupling of backward stimulated Raman scattering (BSRS) and backward stimulated Brillouin scattering (BSBS) in regimes where the reflectivity involves the nonlinear behavior of particles trapped in the daughter plasma waves. The temporal envelope of a Langmuir wave (LW) obeys a Schrödinger equation where the potential is the periodic electron density fluctuation resulting from an ion-acoustic wave (IAW). The BSRS-driven LWs in this case have a Bloch wave structure and a modified dispersion due to the BSBS-driven spatially periodic IAW, which includes frequency band gaps at kLW ∼ kIAW/2 ∼ k0 (kLW, kIAW, and k0 are the wave number of the LW, IAW, and incident pump electromagnetic wave, respectively). This band structure and the associated Bloch wave harmonic components are distinctly observed in RPIC calculations of the electron density fluctuation spectra and this structure may be observable in Thomson scatter. Bloch wave components grow up in the LW spectrum, and are not the result of isolated BSRS. Self-Thomson scattered light from these Bloch wave components can have forward scattering components. The distortion of the LW dispersion curve implies that the usual relationship connecting the frequency shift of the BSRS-scattered light and the density of origin of this light may become inaccurate. The modified LW frequency results in a time-dependent frequency shift that increases as the IAW grows, detunes the BSRS frequency matching condition, and reduces BSRS growth. A dependence of the BSRS reflectivity on the IAW Landau damping results because this damping determines the levels of IAWs. The time-dependent reflectivity in our simulations is characterized by bursts of sub-picosecond pulses of BSRS alternating with multi-ps pulses of BSBS, and BSRS is observed to decline precipitously as soon as SBS begins to grow from low levels. In strong BSBS regimes, the Bloch wave effects in BSRS are strong and temporal anti-correlation with BSRS is due to pump depletion in addition to frequency detuning. In most cases studied, BSBS suppressed the time-averaged reflectivity of BSRS compared to the levels obtained with fixed ions (and therefore no BSBS). The strong spatial modulation of the Bloch Langmuir waves appears to weaken electron trapping and thereby lowers the inflated reflectivity levels of BSRS.
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52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.65.Rr Particle-in-cell method
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
back to top Ionospheric, Solar-System, and Astrophysical Plasmas

Theory and experiments characterizing hypervelocity impact plasmas on biased spacecraft materials

Nicolas Lee, Sigrid Close, Ashish Goel, David Lauben, Ivan Linscott, Theresa Johnson, David Strauss, Sebastian Bugiel, Anna Mocker, and Ralf Srama

Phys. Plasmas 20, 032901 (2013); http://dx.doi.org/10.1063/1.4794331 (9 pages)

Online Publication Date: 4 March 2013

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Space weather including solar activity and background plasma sets up spacecraft conditions that can magnify the threat from hypervelocity impacts. Hypervelocity impactors include both meteoroids, traveling between 11 and 72 km/s, and orbital debris, with typical impact speeds of 10 km/s. When an impactor encounters a spacecraft, its kinetic energy is converted over a very short timescale into energy of vaporization and ionization, resulting in a small, dense plasma. This plasma can produce radio frequency (RF) emission, causing electrical anomalies within the spacecraft. In order to study this phenomenon, we conducted ground-based experiments to study hypervelocity impact plasmas using a Van de Graaff dust accelerator. Iron projectiles ranging from 10−16 g to 10−11 g were fired at speeds of up to 70 km/s into a variety of target materials under a range of surface charging conditions representative of space weather effects. Impact plasmas associated with bare metal targets as well as spacecraft materials were studied. Plasma expansion models were developed to determine the composition and temperature of the impact plasma, shedding light on the plasma dynamics that can lead to spacecraft electrical anomalies. The dependence of these plasma properties on target material, impact speed, and surface charge was analyzed. Our work includes three major results. First, the initial temperature of the impact plasma is at least an order of magnitude lower than previously reported, providing conditions more favorable for sustained RF emission. Second, the composition of impact plasmas from glass targets, unlike that of impact plasmas from tungsten, has low dependence on impact speed, indicating a charge production mechanism that is significant down to orbital debris speeds. Finally, negative ion formation has a strong dependence on target material. These new results can inform the design and operation of spacecraft in order to mitigate future impact-related space weather anomalies and failures.
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52.70.Gw Radio-frequency and microwave measurements
52.25.Tx Emission, absorption, and scattering of particles
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.65.-y Plasma simulation
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