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Dec 2003

Volume 10, Issue 12, pp. 4601-4915

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back to top Basic Plasma Phenomena, Waves, Instabilities

Low-frequency waves in collisional complex plasmas with an ion drift

S. A. Khrapak and V. V. Yaroshenko

Phys. Plasmas 10, 4616 (2003); http://dx.doi.org/10.1063/1.1621398 (6 pages) | Cited 14 times

Online Publication Date: 20 November 2003

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A self-consistent model of low-frequency linear waves in collisional complex (dusty) plasmas with an ion drift is presented. Plasma conditions relevant to recent wave experiments under microgravity conditions are considered. Ion-neutral, ion-dust, and neutral-dust collisions, as well as external forces acting on the grains and grain charge variations in the presence of the wave are taken into account. A linear dispersion relation is obtained and some limiting cases are analyzed. Comparison of the obtained theoretical results with the experiments under microgravity conditions is presented. © 2003 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Excitation of nonreciprocal electromagnetic surface waves in semibounded magnetized plasmas by an electron beam

B. Shokri and B. Jazi

Phys. Plasmas 10, 4622 (2003); http://dx.doi.org/10.1063/1.1623765 (5 pages) | Cited 16 times

Online Publication Date: 20 November 2003

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The dispersion relation of nonreciprocal electromagnetic surface waves propagating on the magnetized plasma–vacuum interface is obtained. Furthermore, the dependency of penetration depth on the magnetic field strength and its directivity is investigated. Finally, it will be shown that by an electron beam flowing on the plasma surface, aforementioned waves can be excited. © 2003 American Institute of Physics.
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52.25.-b Plasma properties

Resonance cones in a dusty magnetized plasma

Thomas Trottenberg, Björn Brede, Dietmar Block, and Alexander Piel

Phys. Plasmas 10, 4627 (2003); http://dx.doi.org/10.1063/1.1624834 (6 pages) | Cited 4 times

Online Publication Date: 20 November 2003

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A new diagnostic method for magnetized dusty plasmas, the excitation of lower hybrid resonance cones, is investigated experimentally. The resonance cone is excited with a small antenna, and the angular distribution of the wave field with respect to the magnetic field shows a resonant enhancement, which shifts according to the free electron density. It is demonstrated that dust reduces the free electron density in agreement with Langmuir probe results. Wave damping by scattering effects is found negligible. © 2003 American Institute of Physics.
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52.25.Xz Magnetized plasmas
52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.70.Gw Radio-frequency and microwave measurements
back to top Nonlinear Phenomena, Turbulence, Transport

Linear theory of nonlocal transport in a magnetized plasma

A. V. Brantov, V. Yu. Bychenkov, W. Rozmus, C. E. Capjack, and R. Sydora

Phys. Plasmas 10, 4633 (2003); http://dx.doi.org/10.1063/1.1624249 (12 pages) | Cited 7 times

Online Publication Date: 20 November 2003

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A system of nonlocal electron-transport equations for small perturbations in a magnetized plasma is derived using the systematic closure procedure of Bychenkov et al. [Phys. Rev. Lett. 75, 4405 (1995)]. Solution to the linearized kinetic equation with a Landau collision operator is obtained in the diffusive approximation. The Fourier components of the longitudinal, oblique, and transversal electron fluxes are found in an explicit form for quasistatic conditions in terms of the generalized forces: the gradients of density and temperature, and the electric field. The full set of nonlocal transport coefficients is given and discussed. Nonlocality of transport enhances electron fluxes across magnetic field above the values given by strongly collisional local theory. Dispersion and damping of magnetohydrodynamic waves in weakly collisional plasmas is discussed. Nonlocal transport theory is applied to the problem of temperature relaxation across the magnetic field in a laser hot spot. © 2003 American Institute of Physics.
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52.25.Fi Transport properties
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.38.Fz Laser-induced magnetic fields in plasmas

The concept of collision strength and a unified kinetic calculation for hard-sphere interactions and inverse square force law interactions

Yongbin Chang

Phys. Plasmas 10, 4645 (2003); http://dx.doi.org/10.1063/1.1625647 (16 pages) | Cited 4 times

Online Publication Date: 20 November 2003

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With a concept of collision strength and other associated definitions, a unified kinetic theory for both hard-sphere interactions and inverse square force law interactions is developed. Collision frequencies that associate with many kinds of physical terms are calculated and expressed by a series special function Υj(α,x). Among them are arbitrary higher order linear Fokker–Planck coefficients, collision frequency, and energy exchange frequency. In case of a two-temperature system, the total collision rate, energy exchange rate, and collision strength rate are calculated and expressed in a uniform expression. A primitive form of Coulomb logarithm ½Γ(0,hmin) is found by comparing the exact form of equilibration time with Spitzer’s result. Many unifications are found from the unified expression. The threshold value of collision strength has unified activation energy in chemical reaction rate theory and ionization energy in Thomson’s classical ionization theory. An incomplete gamma function has unified Arrhenius exponential coefficient in chemical reaction rate theory and Coulomb logarithm in plasma physics. © 2003 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
98.10.+z Stellar dynamics and kinematics
51.10.+y Kinetic and transport theory of gases
82.40.-g Chemical kinetics and reactions: special regimes and techniques

The two-dimensional magnetohydrodynamic Kelvin–Helmholtz instability: Compressibility and large-scale coalescence effects

H. Baty, R. Keppens, and P. Comte

Phys. Plasmas 10, 4661 (2003); http://dx.doi.org/10.1063/1.1624076 (14 pages) | Cited 17 times

Online Publication Date: 20 November 2003

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The Kelvin–Helmholtz (KH) instability occurring in a single shear flow configuration that is embedded in a uniform flow-aligned magnetic field, is revisited by means of high resolution two-dimensional magnetohydrodynamic simulations. First, the calculations extend previous studies of magnetized shear flows to a higher compressibility regime. The nonlinear evolution of an isolated KH billow emerging from the fastest growing linear mode for a convective sonic Mach number Mcs = 0.7 layer is in many respects similar to its less compressible counterpart (Mach Mcs = 0.5). In particular, the disruptive regime where locally amplified, initially weak magnetic fields, control the nonlinear saturation process is found for Alfvén Mach numbers 4≲MA≲30. The most notable difference between Mcs = 0.7 vs Mcs = 0.5 layers is that higher density contrasts and fast magnetosonic shocklet structures are observed. Second, the use of adaptive mesh refinement allows to parametrically explore much larger computational domains, including up to 22 wavelengths of the linearly dominant mode. A strong process of large-scale coalescence is found, whatever the magnetic field regime. It proceeds through continuous pairing/merging events between adjacent vortices up to the point where the final large-scale vortical structure reaches the domain dimensions. This pairing/merging process is attributed to the growth of subharmonic modes and is mainly controlled by relative phase differences between them. These grid-adaptive simulations demonstrate that even in very weak magnetic field regimes (MA ≃ 30), the large-scale KH coalescence process can trigger tearing-type reconnection events previously identified in cospatial current–vortex sheets. © 2003 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.30.-q Plasma dynamics and flow
95.30.Qd Magnetohydrodynamics and plasmas

Electrostatic instabilities and nonlinear structures of low-frequency waves in nonuniform electron–positron–ion plasmas with shear flow

Arshad M. Mirza, Asma Hasan, M. Azeem, and H. Saleem

Phys. Plasmas 10, 4675 (2003); http://dx.doi.org/10.1063/1.1620998 (5 pages) | Cited 6 times

Online Publication Date: 20 November 2003

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It is found that the low-frequency ion acoustic and electrostatic drift waves can become unstable in uniform electron–ion and electron–positron–ion plasmas due to the ion shear flow. In a collisional plasma a drift-dissipative instability can also take place. In the presence of collisions the temporal behavior of nonlinear drift-dissipative mode can be represented in the form of well-known Lorenz and Stenflo type equations that admit chaotic trajectories. On the other hand, a quasi-stationary solution of the mode coupling equations can be represented in the form of monopolar vortex. The results of the present investigation can be helpful in understanding electrostatic turbulence and wave phenomena in laboratory and astrophysical plasmas. © 2003 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
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.)
52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence

Nonlinear slow shear Alfvén wave in electron–positron–ion plasmas

S. Mahmood and H. Saleem

Phys. Plasmas 10, 4680 (2003); http://dx.doi.org/10.1063/1.1622953 (5 pages) | Cited 22 times

Online Publication Date: 20 November 2003

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Nonlinear solitary structures of an arbitrary amplitude slow shear Alfvén wave (SSAW) in ideal electron–positron–ion (e–p–i) plasmas are studied. It is found that the electron density dips of SSAW are formed in the super Alfvénic region. The amplitude and the width of the nonlinear shear Alfvén wave reduces with the increase in the concentration of positrons in electron–ion (e–i) plasmas. The width of the soliton also depends upon the direction of propagation of the perturbation in both e–i and e–p–i plasmas. The numerical results for several different cases have also been presented for illustrative purposes. © 2003 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Sb Solitons; BGK modes
52.25.Kn Thermodynamics of plasmas

Dust acoustic solitary waves and double layers in a dusty plasma with trapped electrons

S. K. El-Labany and W. F. El-Taibany

Phys. Plasmas 10, 4685 (2003); http://dx.doi.org/10.1063/1.1623764 (11 pages) | Cited 27 times

Online Publication Date: 20 November 2003

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The effect of variable dust charge, dust temperature, and trapped electrons on small amplitude dust acoustic waves is investigated. It is found that both compressive and rarefactive solitons as well as double layers exist depending on the nonisothermality parameter. A modified Korteweg–de Vries is derived. At critical density, the Korteweg–de Vries equation is obtained. Employing quasipotential analysis, the Sagdeev potential equation with the inclusion of different new effects has been derived. Because of the presence of free and trapped electrons, the plasma acoustic wave has gained features of various solitary waves. The Sagdeev potential equation, at a small amplitude, shows that the ordering of nonisothermality plays a unique role. In the case of a plasma with first-order nonisothermality, the Sagdeev potential equation shows the compressive solitary wave propagation, while for plasma with higher-order nonisothermality, the solution of this equation reveals the coexistence of both compressive and rarefactive solitary waves. In addition, for certain plasma parameters, the solitary wave disappears and a double layer is expected. Again, with the better approximation in the Sagdeev potential equation, more features of solitary waves, e.g., spiky and explosive, along with the double layers, are also highlighted. The findings of this investigation may be useful in understanding laboratory plasma phenomena and astrophysical situations. © 2003 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes

Confinement and dynamical regulation in two-dimensional convective turbulence

N. H. Bian and O. E. Garcia

Phys. Plasmas 10, 4696 (2003); http://dx.doi.org/10.1063/1.1625941 (12 pages) | Cited 14 times

Online Publication Date: 20 November 2003

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In this work the nature of confinement improvement implied by the self-consistent generation of mean flows in two-dimensional convective turbulence is studied. The confinement variations are linked to two distinct regulation mechanisms which are also shown to be at the origin of low-frequency bursting in the fluctuation level and the convective heat flux integral, both resulting in a state of large-scale intermittency. The first one involves the control of convective transport by sheared mean flows. This regulation relies on the conservative transfer of kinetic energy from tilted fluctuations to the mean component of the flow. Bursting can also result from the quasi-linear modification of the linear instability drive which is the mean pressure gradient. For each bursting process the relevant zero-dimensional model equations are given. These are finally coupled in a minimal model of convection in fluids and plasmas. The results of the modeling are used to discuss confinement scaling and intermittency, and in a heuristic way, more complex issues such as criticality and transport avalanches. © 2003 American Institute of Physics.
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52.35.Ra Plasma turbulence

Unified form for parallel ion viscous stress in magnetized plasmas

E. D. Held

Phys. Plasmas 10, 4708 (2003); http://dx.doi.org/10.1063/1.1626681 (8 pages) | Cited 5 times

Online Publication Date: 20 November 2003

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In this work a unified form for the parallel ion viscous stress in a magnetized plasma is presented. Approximately valid for arbitrary collisionality, the integral nature of this generalized closure results from assuming the maximal ordering between collisional pitch-angle scattering and free streaming effects and from taking a Chapman–Enskog-type approach which includes the parallel ion viscous stress itself as a drive. The ion drift kinetic equation is solved in a sheared slab using an expansion in eigenfunctions of the Lorentz scattering operator. Integrating the coefficient equations in space and taking the proper velocity space moments couples the parallel viscous stress closure to an integral momentum restoring term, thus generalizing the concept of momentum conservation for simplified Coulomb collision operators. The integral closure involves following ions along magnetic field lines which are the ideal, time-independent characteristics of the perturbed distribution function. The fact that the viscous stress and momentum restoring term appear in the kernels of these field line integrals means that in general the closure has the form of coupled Volterra equations with an inhomogeneous term supplied by the traditional flow gradient drive. It is shown that the unified closure agrees both qualitatively and quantitatively with previous results and hence represents a generalized physical form for the parallel ion viscous stress in magnetized plasmas. © 2003 American Institute of Physics.
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52.25.Dg Plasma kinetic equations
back to top Magnetically Confined Plasmas, Heating, Confinement

Marginal stability boundaries for infinite-n ballooning modes in a quasiaxisymmetric stellarator

S. R. Hudson and C. C. Hegna

Phys. Plasmas 10, 4716 (2003); http://dx.doi.org/10.1063/1.1622669 (12 pages) | Cited 8 times

Online Publication Date: 20 November 2003

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A method for computing the ideal magnetohydrodynamic (MHD) stability boundaries in three-dimensional equilibria is employed. Following Hegna and Nakajima [Phys. Plasmas 5, 1336 (1998)], a two-dimensional family of equilibria is constructed by perturbing the pressure and rotational-transform profiles in the vicinity of a flux surface for a given stellarator equilibrium. The perturbations are constrained to preserve the MHD equilibrium condition. For each perturbed equilibrium, the infinite-n ballooning stability is calculated. Marginal stability diagrams are thus constructed that are analogous to (s,α) diagrams for axisymmetric configurations. A quasiaxisymmetric stellarator is considered. Calculations of stability boundaries generally show regions of instability can occur for either sign of the average magnetic shear. Additionally, regions of second-stability are present. © 2003 American Institute of Physics.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Kn Thermodynamics of plasmas
52.75.-d Plasma devices
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects

Plasma flow and confinement in the vicinity of a rotating island in tokamaks

K. C. Shaing

Phys. Plasmas 10, 4728 (2003); http://dx.doi.org/10.1063/1.1623198 (9 pages) | Cited 12 times

Online Publication Date: 20 November 2003

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The theory for the electric field and the plasma confinement in the vicinity of a magnetic island in tokamaks [Phys. Plasmas 9, 3470 (2002)] is extended to the situation where the magnetic island is rotating. The electric field that is parallel to the magnetic field, E∥, is assumed to vanish. With this assumption, the theory for a nonrotating island is applicable to a rotating island if the radial electric field in the nonrotating theory is replaced by the radial gradient of F. Here, F is the part of the electrostatic potential that is constant on the rotating island magnetic surface. As an application of the theory, the radial electric field, toroidal flow speed, ambipolar particle flux, heat flux, and island rotation frequency in the collisionless regime are also presented. © 2003 American Institute of Physics.
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52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks

Role of the m = 0 modes in the edge region of a reversed-field pinch during pulsed poloidal current drive

A. Cravotta, G. Spizzo, P. Zanca, and P. Martin

Phys. Plasmas 10, 4737 (2003); http://dx.doi.org/10.1063/1.1623271 (7 pages) | Cited 4 times

Online Publication Date: 20 November 2003

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Changes in the edge profile of soft x-ray emission during pulsed poloidal current drive (PPCD) experiments are in agreement with the modifications of the plasma surface, as seen from magnetic measurements. In particular, the m = 0 modes resonant at the reversal radius have been analyzed. A comparison with an m = 0 island reconstruction model shows that PPCD reduces the bulging associated with the m = 0 modes by shifting inward the reversal surface, where the m = 0 island is located. Regarding the total m = 0 amplitude, there are evidences that during PPCD, on average, it does not change significantly. Additional data coming from standard discharges support the idea that two competing phenomena act during PPCD: one is the inward shift of the reversal, which destabilizes the m = 0 modes; the other one is the decrease of the m = 1 fluctuations, which acts in the opposite direction. © 2003 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.55.Wq Current drive; helicity injection
52.55.Tn Ideal and resistive MHD modes; kinetic modes

Drift-ordered fluid equations for field-aligned modes in low-β collisional plasma with equilibrium pressure pedestals

Andrei N. Simakov and Peter J. Catto

Phys. Plasmas 10, 4744 (2003); http://dx.doi.org/10.1063/1.1623492 (14 pages) | Cited 27 times

Online Publication Date: 20 November 2003

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See Also: Erratum

Show Abstract
Starting from the complete short mean-free path fluid equations describing magnetized plasmas, assuming that plasma pressure is small compared to magnetic pressure, considering field-aligned plasma fluctuations, and adopting an ordering in which the plasma species flow velocities are much smaller than the ion thermal speed, a system of nonlinear equations for plasma density, electron and ion temperatures, parallel ion flow velocity, parallel current, electrostatic potential, perturbed parallel electromagnetic potential, and a perturbed magnetic field is derived. The equations obtained allow sharp equilibrium radial gradients of plasma quantities, and are shown to contain the neoclassical (Pfirsch–Schlüter) results for plasma current, parallel ion flow velocity (with the correct temperature gradient terms), and parallel gradients of equilibrium electron and ion temperatures. Special care is taken to ensure the divergence-free character of perturbed magnetic field and total plasma current, as well as local particle number and total energy conservation. © 2003 American Institute of Physics.
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52.25.Gj Fluctuation and chaos phenomena

Stability of the ion-temperature-gradient-driven mode with negative magnetic shear

M. Uchida, S. Sen, A. Fukuyama, and D. R. McCarthy

Phys. Plasmas 10, 4758 (2003); http://dx.doi.org/10.1063/1.1616015 (5 pages) | Cited 2 times

Online Publication Date: 20 November 2003

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A model for transition to the enhanced reverse shear or negative central shear mode triggered in tokamaks is proposed. This model takes into account the linear behavior of the ion temperature gradient (ITG) driven perturbation, considered nowadays as the dominant source of anomalous energy losses in the low confinement mode, in the presence of a radially varying parallel velocity. Analytic and numerical studies show that when the magnetic shear has the same sign as the second derivative of the parallel velocity with respect to the radial coordinate, the ITG mode may become more unstable. On the other hand, when the magnetic shear has the opposite sign to the second derivative of the parallel velocity, the linear ITG mode may be completely stabilized. This result is similar to our earlier works on parallel velocity shear instability [S. Sen et al., Phys. Plasmas 7, 1192 (2000); D. R. McCarthy et al., Phys. Plasmas 8, 3645 (2001)]. © 2003 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Separatrix shapes and internal structures of a field-reversed configuration plasma

Hiroshi Gota, Kayoko Fujimoto, Yasunori Ohkuma, Tsutomu Takahashi, and Yasuyuki Nogi

Phys. Plasmas 10, 4763 (2003); http://dx.doi.org/10.1063/1.1624835 (8 pages) | Cited 9 times

Online Publication Date: 20 November 2003

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The separatrix shape of a field-reversed configuration plasma is determined in comparison with measured fluxes surrounding the plasma and the solution of the Grad–Shafranov equation with an edge-layer plasma in the open field region. A reconnection point of the bias field, an outgoing flow of torn plasmas and a large amplitude ripple on the separatrix surface are clearly observed at the formation phase. A smoothed separatrix shape having definite ends is observed at the quiescent phase. It is also estimated that the beta value at the separatrix and the thickness of the edge-layer plasma are, respectively, βs = 0.5–0.7 and 4–6 ρi (ρi: ion gyroradius). The magnetic structure inside the separatrix is investigated by solving the Grad–Shafranov equation with the measured separatrix shape and βs. It is found that magnetic islands are formed near the magnetic axis not only at the formation phase but also at the quiescent phase. The appearance and coalescence of the islands are repeated during the discharge. © 2003 American Institute of Physics.
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52.55.Ez Theta pinch
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.40.Hf Plasma-material interactions; boundary layer effects

Destabilization of fast magnetoacoustic waves by circulating energetic ions in toroidal plasmas

V. S. Belikov, Ya. I. Kolesnichenko, and R. B. White

Phys. Plasmas 10, 4771 (2003); http://dx.doi.org/10.1063/1.1625375 (5 pages) | Cited 6 times

Online Publication Date: 20 November 2003

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An instability of fast magnetoacoustic waves driven by circulating energetic ions in axisymmetric toroidal plasmas and characterized by frequencies below the ion gyrofrequency is considered. An important role of the l = 0 resonance (l is the number of a cyclotron harmonic) in the wave–particle interaction is revealed: It is shown that this resonance considerably extends an unstable region in the space of the pitch-angles of the energetic ions and the wave frequencies. The analysis is carried out for a “slow” instability, which has the growth rate less than the bounce frequency of the energetic ions. Specific examples relevant to the National Spherical Torus Experiment [Spitzer et al., Fusion Technol. 30, 1337 (1996)], where instabilities of this kind were observed, are considered. © 2003 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Dm Sound waves

Analysis of stable resistive wall modes in a rotating plasma

A. M. Garofalo, T. H. Jensen, and E. J. Strait

Phys. Plasmas 10, 4776 (2003); http://dx.doi.org/10.1063/1.1625942 (8 pages) | Cited 39 times

Online Publication Date: 20 November 2003

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Measurements of the resistive wall mode (RWM) response to external resonant field pulses yield complete knowledge of the mode characteristics in the parameter range explored. An ideal magnetohydrodynamics model [Garofalo et al., Phys. Plasmas 9, 4573 (2002)] has been generalized to include the effects of plasma rotation and dissipation, and the new model is found to explain quantitatively the experimental observations. Rotation of the RWM with respect to the wall is often described as an essential feature of the mechanism by which plasma rotation stabilizes the RWM. This interpretation of the rotational stabilization of the RWM appears inconsistent with the measurements from recent DIII–D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] experiments. It is found that the theoretically predicted mode rotation with respect to the wall is not needed for stabilization and is only a consequence of torque balance in the absence of magnetic-field nonaxisymmetries. © 2003 American Institute of Physics.
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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.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Fa Tokamaks, spherical tokamaks
back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

First observation of density profile in directly laser-driven polystyrene targets for ablative Rayleigh–Taylor instability research

Shinsuke Fujioka, Hiroyuki Shiraga, Masaharu Nishikino, Keisuke Shigemori, Atsushi Sunahara, Mitsuo Nakai, Hiroshi Azechi, Katsunobu Nishihara, and Tatsuhiko Yamanaka

Phys. Plasmas 10, 4784 (2003); http://dx.doi.org/10.1063/1.1622951 (6 pages) | Cited 8 times

Online Publication Date: 20 November 2003

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The temporal evolution of the density profile of a directly laser-driven polystyrene target was observed for the first time using an x-ray penumbral imaging technique coupled with side-on x-ray backlighting at the GEKKO XII [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)]–High Intensity Plasma Experimental Research laser facility (IL = 0.7×1014 W/cm2, λL = 0.35 μm). This density measurement makes it possible to experimentally confirm all physical parameters [γ(k),k,g,math,ρa,Lm] appearing in the modified Takabe formula for the growth rate of the ablative Rayleigh–Taylor instability. The measured density profiles were well reproduced by a one-dimensional hydrodynamic simulation code. The density measurement contributes toward fully understanding the ablative Rayleigh–Taylor instability. © 2003 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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.)
52.70.La X-ray and γ-ray measurements

Length scaling of dynamic-hohlraum axial radiation

T. W. L. Sanford, R. C. Mock, S. A. Slutz, and D. L. Peterson

Phys. Plasmas 10, 4790 (2003); http://dx.doi.org/10.1063/1.1625938 (10 pages) | Cited 13 times

Online Publication Date: 20 November 2003

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Radiation generated within a 10-mm-long foam-target DH (dynamic hohlraum) is used for high-temperature (>200 eV) radiation-flow and inertial-confinement-fusion studies [Sanford et al., Phys. Plasmas 9, 3573 (2002)]. The length of this DH is varied from 5 to 20 mm, keeping the mass/unit length constant in an effort to study the scaling of axial radiation power with length, and better understand its production. Measurements show a greater variation in this power with length than would be expected from simple arguments [Slutz et al., Phys. Plasmas 8, 1673 (2001)]. Maximum axial power of ∼ 10 TW is produced with a length of ∼ 7.5 mm, similar to the typical power for the baseline 10 mm DH. The decreasing axial power (at a rate of ∼ 0.65 TW per mm at longer lengths) is bounded by radiation-magnetohydrodynamic simulations [Peterson et al., Phys. Plasmas 6, 2178 (1999)] that include the development of the magnetic Rayleigh–Taylor instability in the r–z plane. The dramatic drop in axial power below 7.5 mm, by contrast, was unanticipated. This decrease suggests the presence of differing mechanisms for limiting power at short and long lengths. © 2003 American Institute of Physics.
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52.57.-z Laser inertial confinement
52.55.Ez Theta pinch
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
back to top Ionospheric, Solar-system, and Astrophysical Plasmas

Plasma heating via parametric beating of Alfvén waves, with heliospheric applications

Steven H. Bekhor and R. Paul Drake

Phys. Plasmas 10, 4800 (2003); http://dx.doi.org/10.1063/1.1619975 (11 pages) | Cited 1 time

Online Publication Date: 20 November 2003

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This paper advances a novel mechanism to explain the dissipation of the Alfvén waves that carry much of the energy in heliospheric and astrophysical turbulence, with specific applications to solar wind heating. The essential point is that the nonlinear beating of relatively low-frequency Alfvén waves, which are abundant in the heliosphere, drives a compressible magnetosonic response whose damping can dissipate significant energy. This mechanism involves both kinetic and magnetohydrodynamic (MHD) processes. The damping of the magnetosonic waves is a kinetic process. The nonlinear beating of Alfvén waves, which produces the magnetosonic waves, is best described by MHD theory. This mechanism complements and may compete with the well-known alternative mechanism in which the cascade of turbulent energy to small-scale, high-frequency Alfvén waves dissipates by ion-cyclotron damping. The MHD analysis in this paper reveals that the fast magnetosonic mode dominates the dissipation when the plasma beta is near unity, and that the timescale of dissipation in the heliosphere can vary from hours to a year depending upon the direction of the driven wave and the plasma parameters where it is driven. The damping of the driven magnetosonic waves may also contribute to the observed high-energy particle distributions. © 2003 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.50.-b Plasma production and heating
96.20.Br Origin and evolution
96.60.Vg Particle emission, solar wind
52.35.Ra Plasma turbulence
95.30.Qd Magnetohydrodynamics and plasmas
back to top Lasers, Particle Beams, Accelerators, Radiation Generation

The role of the focusing field profile on the stability of periodically focused particle beams

J. S. Moraes, F. B. Rizzato, and R. Pakter

Phys. Plasmas 10, 4811 (2003); http://dx.doi.org/10.1063/1.1619139 (7 pages) | Cited 2 times

Online Publication Date: 20 November 2003

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In this paper, the role of the focusing field profile on the stability of periodically focused particle beams is investigated, paying special attention to the transport within the new regions of stability found recently for vacuum-phase advances well above 90° [R. Pakter and F. B. Rizzato, Phys. Rev. Lett. 87, 044801 (2001)]. In particular, a solenoidal focusing field profile that goes from a smooth sinusoidal-like function to a sharp-edged step-funcion as a continuous parameter is varied is considered. It is shown that the new regions are always present, but may be very sensitive to changes in the focusing field profile. Specifically, as the focusing field becomes more localized, the new regions become narrower, occur at higher vacuum phase advances, and present a larger number of nonlinear resonances and chaos in the beam envelope phase space. Although in all the cases analyzed here it was found that there is a relatively thick layer of regular trajectories isolating the matched solution from the chaotic region, self-consistent simulations show that envelope phase-space chaos may affect beam dynamics, leading to some small emittance growth. © 2003 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
41.85.-p Beam optics

X-ray generation in an ion channel

I. Kostyukov, S. Kiselev, and A. Pukhov

Phys. Plasmas 10, 4818 (2003); http://dx.doi.org/10.1063/1.1624605 (11 pages) | Cited 45 times

Online Publication Date: 20 November 2003

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X-ray generation by relativistic electrons in an ion channel is studied. The emission process is analyzed in the regime of high harmonic generation when the plasma wiggler strength is large. Like for the conventional free electron laser, the synchrotron-like broadband spectrum is generated in this regime. An asymptotic expression for the radiation spectrum of the spontaneous emission is derived. The radiation spectrum emitted from an axisymmetric monoenergetic electron beam is analyzed. The stimulated emission in the ion channel is studied and the gain of the ion-channel synchrotron-radiation laser is calculated. It is shown that the use of laser-produced ion channels leads to a much higher power of x-ray radiation than the one in a self-generated channel. In addition, the mean photon energy, the number of emitted photons and the brilliance of the photon beam increase dramatically. Three-dimensional particle-in-cell simulations of a 25-GeV electron bunch propagating in a laser-produced ion channel are made. Several GeV γ-quants are produced in a good agreement with the analytical results. © 2003 American Institute of Physics.
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41.60.Ap Synchrotron radiation
52.40.Mj Particle beam interactions in plasmas

Electromagnetic Weibel instability in intense charged particle beams with large energy anisotropy

Edward A. Startsev and Ronald C. Davidson

Phys. Plasmas 10, 4829 (2003); http://dx.doi.org/10.1063/1.1625648 (8 pages) | Cited 18 times

Online Publication Date: 20 November 2003

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In plasmas with strongly anisotropic distribution functions, collective instabilities may develop if there is sufficient coupling between the transverse and longitudinal degrees of freedom. Our previous numerical and theoretical studies of intense charged particle beams with large temperature anisotropy [E. A. Startsev, R. C. Davidson, and H. Qin, Phys. Rev. ST Accel. Beams 6, 084401 (2003); Phys. Plasmas 9, 3138 (2002)] demonstrated that a fast, electrostatic, Harris-type instability develops, and saturates nonlinearly, for sufficiently large temperature anisotropy (T⊥b/T∥b≫1). The total distribution function after saturation, however, is still far from equipartitioned. In this paper the linearized Vlasov–Maxwell equations are used to investigate detailed properties of the transverse electromagnetic Weibel-type instability for a long charge bunch propagating through a cylindrical pipe of radius rw. The kinetic stability analysis is carried out for azimuthally symmetric perturbations about a two-temperature thermal equilibrium distribution in the smooth-focusing approximation. The most unstable modes are identified, and their eigenfrequencies, radial mode structure and instability thresholds are determined. The stability analysis shows that, although there is free energy available to drive the electromagnetic Weibel instability, the finite transverse geometry of the charged particle beam introduces a large threshold value for the temperature anisotropy [(T⊥b/T∥b)Weibel≫(T⊥b/T∥b)Harris] below which the instability is absent. Hence, unlike the case of an electrically neutral plasma, the Weibel instability is not expected to play as significant a role in the process of energy isotropization of intense unneutralized charged particle beams as the electrostatic Harris-type instability. © 2003 American Institute of Physics.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
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