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May 2012

Volume 19, Issue 5 (partial)

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back to top Basic Plasma Phenomena, Waves, Instabilities

Magnetohydrodynamic spin waves in degenerate electron-positron-ion plasmas

A. Mushtaq, R. Maroof, Zulfiaqr Ahmad, and A. Qamar

Phys. Plasmas 19, 052101 (2012); http://dx.doi.org/10.1063/1.4714602 (7 pages)

Online Publication Date: 16 May 2012

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Low frequency magnetosonic waves are studied in magnetized degenerate electron-positron-ion plasmas with spin effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, and spin magnetization energy, a generalized dispersion relation for oblique magnetosonic waves is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. For three different values of angle θ, the generalized dispersion relation is reduced to three different relations under the low frequency magnetohydrodynamic assumptions. It is found that the effect of quantum corrections in the presence of positron concentration significantly modifies the dispersive properties of these modes. The importance of the work relevant to compact astrophysical bodies is pointed out.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Hamiltonian magnetohydrodynamics: Helically symmetric formulation, Casimir invariants, and equilibrium variational principles

T. Andreussi, P. J. Morrison, and F. Pegoraro

Phys. Plasmas 19, 052102 (2012); http://dx.doi.org/10.1063/1.4714761 (8 pages)

Online Publication Date: 16 May 2012

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The noncanonical Hamiltonian formulation of magnetohydrodynamics (MHD) is used to construct variational principles for continuously symmetric equilibrium configurations of magnetized plasma, including flow. In particular, helical symmetry is considered, and results on axial and translational symmetries are retrieved as special cases of the helical configurations. The symmetry condition, which allows the description in terms of a magnetic flux function, is exploited to deduce a symmetric form of the noncanonical Poisson bracket of MHD. Casimir invariants are then obtained directly from the Poisson bracket. Equilibria are obtained from an energy-Casimir principle and reduced forms of this variational principle are obtained by the elimination of algebraic constraints.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
02.10.-v Logic, set theory, and algebra
02.30.Xx Calculus of variations
02.50.Ey Stochastic processes

Coupling between whistler waves and slow-mode solitary waves

A. Tenerani, F. Califano, F. Pegoraro, and O. Le Contel

Phys. Plasmas 19, 052103 (2012); http://dx.doi.org/10.1063/1.4717764 (10 pages)

Online Publication Date: 18 May 2012

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The interplay between electron- and ion-scale phenomena is of general interest for both laboratory and space plasma physics. In this paper, we investigate the linear coupling between whistler waves and slow magnetosonic solitons through two-fluid numerical simulations. Whistler waves can be trapped in the presence of inhomogeneous external fields such as a density hump or hole where they can propagate for times much longer than their characteristic time scale, as shown by laboratory experiments and space measurements. Space measurements have detected whistler waves also in correspondence to magnetic holes, i.e., to density humps with magnetic field minima extending on ion-scales. This raises the interesting question of how ion-scale structures can couple to whistler waves. Slow magnetosonic solitons share some of the main features of a magnetic hole. Using the ducting properties of an inhomogeneous plasma as a guide, we present a numerical study of whistler waves that are trapped and transported inside propagating slow magnetosonic solitons.
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52.35.Sb Solitons; BGK modes
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
back to top Nonlinear Phenomena, Turbulence, Transport

Electron kappa distribution and steady-state Langmuir turbulence

Peter H. Yoon

Phys. Plasmas 19, 052301 (2012); http://dx.doi.org/10.1063/1.4710515 (6 pages)

Online Publication Date: 4 May 2012

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In a recent pair of papers, the present author discussed a self-consistent theory of asymptotically steady-state electron distribution function and Langmuir turbulence intensity in one [P. H. Yoon, Phys. Plasmas 18, 122303 (2011)] and three [P. H. Yoon, Phys. Plasmas 19, 012304 (2012)] dimensions. The resulting electron distribution function is a type of kappa distribution that features a non-Maxwellian energetic tail component. However, while the one-dimensional solution is rigorously correct, the three-dimensional solution, which was obtained using the cylindrical coordinate representation, contains two features that may be inconsistent for field-free plasmas. One is the assumption that the resonance condition can be approximated by ω-k·v ≈ ω-k∥v∥. Needless to say, this is not the most general condition. The second inconsistency is that while the electron distribution is isotropic in velocity, the Langmuir turbulence intensity depends on the wave propagation direction. While these features may not be too unrealistic in the presence of an implicit ambient magnetic field, they certainly cannot be correct if the plasma is genuinely unmagnetized. In the present paper, we rectify such shortcomings by properly reformulating the problem using a spherical coordinate system in a truly free-field plasma.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Ra Plasma turbulence

Effect of nonthermal electrons on oblique electrostatic excitations in a magnetized electron-positron-ion plasma

H. Alinejad

Phys. Plasmas 19, 052302 (2012); http://dx.doi.org/10.1063/1.4714609 (6 pages)

Online Publication Date: 14 May 2012

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The linear and nonlinear propagation of ion-acoustic waves are investigated in a magnetized electron-positron-ion (e-p-i) plasma with nonthermal electrons. In the linear regime, the propagation of two possible modes and their evolution are studied via a dispersion relation. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. Then, the Korteweg-de Vries equation describing the dynamics of ion-acoustic solitary waves is derived from a weakly nonlinear analysis. The influence on the solitary wave characteristics of relevant physical parameters such as nonthermal electrons, magnetic field, obliqueness, positron concentration, and temperature ratio is examined. It is observed that the increasing nonthermal electrons parameter makes the solitary structures much taller and narrower. Also, it is revealed that the magnetic field strength makes the solitary waves more spiky. The present investigation contributes to the physics of the nonlinear electrostatic ion-acoustic waves in space and laboratory e-p-i plasmas in which wave damping produces an electron tail.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
02.10.-v Logic, set theory, and algebra
52.25.-b Plasma properties

Tripolar vortex formation in dense quantum plasma with ion-temperature-gradients

Anisa Qamar, Ata-ur-Rahman, and Arshad M. Mirza

Phys. Plasmas 19, 052303 (2012); http://dx.doi.org/10.1063/1.4714648 (5 pages)

Online Publication Date: 16 May 2012

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We have derived system of nonlinear equations governing the dynamics of low-frequency electrostatic toroidal ion-temperature-gradient mode for dense quantum magnetoplasma. For some specific profiles of the equilibrium density, temperature, and ion velocity gradients, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. These results are relevant to understand nonlinear structure formation in dense quantum plasmas in the presence of equilibrium ion-temperature and density gradients.
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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.)
52.25.Fi Transport properties

Hexagonal superlattice pattern consisting of colliding filament pairs in a dielectric barrier discharge

Lifang Dong, Ben Li, Ning Lu, Xinchun Li, and Zhongkai Shen

Phys. Plasmas 19, 052304 (2012); http://dx.doi.org/10.1063/1.4717466 (5 pages)

Online Publication Date: 17 May 2012

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Colliding-pairs hexagonal superlattice pattern (CPHSP) is studied in a dielectric barrier discharge system. The evolution of CPHSP bifurcating from a hexagonal pattern to chaos is shown. The phase diagrams of CPHSP as a function of discharge parameters are given. From a series of pictures taken by a high speed video camera, collisions between two spots are observed and the superposition of many collisions results in each big spot presenting four small spots on long time scales. Measurements of the correlation between filaments indicate that the pattern is an interleaving of four different transient hexagonal sublattices. Depending on the discharging sequence, the forces exerted on one colliding spot are discussed briefly.
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52.20.-j Elementary processes in plasmas
52.25.Gj Fluctuation and chaos phenomena
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges

Energy spectrum, dissipation, and spatial structures in reduced Hall magnetohydrodynamic

L. N. Martin, P. Dmitruk, and D. O. Gomez

Phys. Plasmas 19, 052305 (2012); http://dx.doi.org/10.1063/1.4717728 (6 pages)

Online Publication Date: 18 May 2012

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We analyze the effect of the Hall term in the magnetohydrodynamic turbulence under a strong externally supported magnetic field, seeing how this changes the energy cascade, the characteristic scales of the flow, and the dynamics of global magnitudes, with particular interest in the dissipation. Numerical simulations of freely evolving three-dimensional reduced magnetohydrodynamics are performed, for different values of the Hall parameter (the ratio of the ion skin depth to the macroscopic scale of the turbulence) controlling the impact of the Hall term. The Hall effect modifies the transfer of energy across scales, slowing down the transfer of energy from the large scales up to the Hall scale (ion skin depth) and carrying faster the energy from the Hall scale to smaller scales. The final outcome is an effective shift of the dissipation scale to larger scales but also a development of smaller scales. Current sheets (fundamental structures for energy dissipation) are affected in two ways by increasing the Hall effect, with a widening but at the same time generating an internal structure within them. In the case where the Hall term is sufficiently intense, the current sheet is fully delocalized. The effect appears to reduce impulsive effects in the flow, making it less intermittent.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations
52.25.Fi Transport properties
back to top Magnetically Confined Plasmas, Heating, Confinement

Gauge properties of the guiding center variational symplectic integrator

J. Squire, H. Qin, and W. M. Tang

Phys. Plasmas 19, 052501 (2012); http://dx.doi.org/10.1063/1.4714608 (7 pages)

Online Publication Date: 14 May 2012

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Variational symplectic algorithms have recently been developed for carrying out long-time simulation of charged particles in magnetic fields [H. Qin and X. Guan, Phys. Rev. Lett. 100, 035006 (2008); H. Qin, X. Guan, and W. Tang, Phys. Plasmas (2009); J. Li, H. Qin, Z. Pu, L. Xie, and S. Fu, Phys. Plasmas 18, 052902 (2011)]. As a direct consequence of their derivation from a discrete variational principle, these algorithms have very good long-time energy conservation, as well as exactly preserving discrete momenta. We present stability results for these algorithms, focusing on understanding how explicit variational integrators can be designed for this type of system. It is found that for explicit algorithms, an instability arises because the discrete symplectic structure does not become the continuous structure in the t→0 limit. We examine how a generalized gauge transformation can be used to put the Lagrangian in the “antisymmetric discretization gauge,” in which the discrete symplectic structure has the correct form, thus eliminating the numerical instability. Finally, it is noted that the variational guiding center algorithms are not electromagnetically gauge invariant. By designing a model discrete Lagrangian, we show that the algorithms are approximately gauge invariant as long as A and φ are relatively smooth. A gauge invariant discrete Lagrangian is very important in a variational particle-in-cell algorithm where it ensures current continuity and preservation of Gauss’s law [J. Squire, H. Qin, and W. Tang (to be published)].
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52.65.-y Plasma simulation
02.30.Xx Calculus of variations
02.60.Jh Numerical differentiation and integration

Kinetic damping of resistive wall modes in ITER

I. T. Chapman, Y. Q. Liu, O. Asunta, J. P. Graves, T. Johnson, and M. Jucker

Phys. Plasmas 19, 052502 (2012); http://dx.doi.org/10.1063/1.4714877 (10 pages)

Online Publication Date: 15 May 2012

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Full drift kinetic modelling including finite orbit width effects has been used to assess the passive stabilisation of the resistive wall mode (RWM) that can be expected in the ITER advanced scenario. At realistic plasma rotation frequency, the thermal ions have a stabilising effect on the RWM, but the stability limit remains below the target plasma pressure to achieve Q = 5. However, the inclusion of damping arising from the fusion-born alpha particles, the NBI ions, and ICRH fast ions extends the RWM stability limit above the target β for the advanced scenario. The fast ion damping arises primarily from finite orbit width effects and is not due to resonance between the particle frequencies and the instability.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.50.Gj Plasma heating by particle beams
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Auxiliary ECR heating system for the gas dynamic trap

A. G. Shalashov, E. D. Gospodchikov, O. B. Smolyakova, P. A. Bagryansky, V. I. Malygin, and M. Thumm

Phys. Plasmas 19, 052503 (2012); http://dx.doi.org/10.1063/1.4717757 (8 pages)

Online Publication Date: 16 May 2012

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Physics aspects of a new system for electron cyclotron resonance heating (ECRH) at the magnetic mirror device Gas Dynamic Trap (GDT, Budker Institute, Novosibirsk) are discussed. This system based on two 400 kW/54.5 GHz gyrotrons is aimed at increasing the electron temperature up to the range 250–350 eV for improved energy confinement of hot ions. The key physical issue of the GDT magnetic field topology is that conventional ECRH geometries are not accessible. The proposed solution is based on a peculiar effect of radiation trapping in inhomogeneous magnetized plasma. Under specific conditions, oblique launch of gyrotron radiation results in generation of right-hand-polarized (R) electromagnetic waves propagating with high N|| in the vicinity of the cyclotron resonance layer, which leads to effective single-pass absorption of the injected microwave power. In the present paper, we investigate numerically an optimized ECRH scenario based on the proposed mechanism of wave propagation and discuss the design of the ECRH system, which is currently under construction at the Budker Institute.
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52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
02.60.-x Numerical approximation and analysis
52.25.Xz Magnetized plasmas
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Drift wave dispersion relation for arbitrarily collisional plasma

Justin R. Angus and Sergei I. Krasheninnikov

Phys. Plasmas 19, 052504 (2012); http://dx.doi.org/10.1063/1.4714614 (7 pages)

Online Publication Date: 17 May 2012

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The standard local linear analysis of drift waves in a plasma slab is generalized to be valid for arbitrarily collisional electrons by considering the electrons to be governed by the drift-kinetic equation with a BGK-like (Bhatnagar-Gross-Krook) collision operator. The obtained dispersion relation reduces to that found from collisionless kinetic theory when the collision frequency is zero. Electron temperature fluctuations must be retained in the standard fluid analysis in order to obtain good quantitative agreement with our general solution in the highly collisional limit. Any discrepancies between the fluid solution and our general solution in this limit are attributed to the limitations of the BGK collision operator. The maximum growth rates in both the collisional and collisionless limits are comparable and are both on the order of the fundamental drift wave frequency. The main role of the destabilizing mechanism is found to be in determining the parallel wave number at which the maximum growth rate will occur. The parallel wave number corresponding to the maximum growth rate is set by the wave-particle resonance condition in the collisionless limit and transitions to being set by the real frequency being on the order of the rate for electrons to diffuse a parallel wavelength in the collisional limit.
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52.35.Kt Drift waves
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.20.Fs Electron collisions
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties

On the delayed gas breakdown in a ringing theta-pinch with bias magnetic field

Warner C. Meeks and Joshua L. Rovey

Phys. Plasmas 19, 052505 (2012); http://dx.doi.org/10.1063/1.4717731 (7 pages)

Online Publication Date: 17 May 2012

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A single particle model and particle-in-cell simulations are used to elucidate the breakdown physics in a ringing theta-pinch with a bias magnetic field. Previous experimental results show that gas breakdown occurs when the bias magnetic field is nullified by the theta-pinch magnetic field. The analyses presented here agree with the experimental results and show that electron kinetic energy does not exceed the ionization threshold of deuterium until the net magnetic field is approximately zero. Despite the presence of a strong electric field, the gyromotion of electrons within the bias magnetic field prevents them from gaining energy necessary to ionize the gas. Parametric analysis of the peak electron energy as a function of the bias and pre-ionization magnetic fields reveals that: (1) when the bias magnetic field is ≈97% of the pre-ionization magnetic field, peak electron energies are highly erratic resulting in poor overall ionization, and (2) full ionization with repeatable behavior requires a pre-ionization to bias magnetic field ratio of approximately 2 to 1 or higher.
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52.55.Ez Theta pinch
52.65.Rr Particle-in-cell method
52.25.Jm Ionization of plasmas

Measurements of the runaway electron energy during disruptions in the tokamak TEXTOR

M. Forster, K. H. Finken, M. Lehnen, O. Willi, Y. Xu, and TEXTOR Team

Phys. Plasmas 19, 052506 (2012); http://dx.doi.org/10.1063/1.4717759 (10 pages)

Online Publication Date: 18 May 2012

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Calorimetric measurements of the total runaway electron energy are carried out using a reciprocating probe during induced TEXTOR disruptions. A comparison with the energy inferred from runaway energy spectra, which are measured with a scintillator probe, is used as an independent check of the results. A typical runaway current of 100 kA at TEXTOR contains 30 to 35 kJ of runaway energy. The dependencies of the runaway energy on the runaway current, the radial probe position, the toroidal magnetic field and the predisruptive plasma current are studied. The conversion efficiency of the magnetic plasma energy into runaway energy is calculated to be up to 26%.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Fa Tokamaks, spherical tokamaks
back to top Inertially Confined Plasmas, High Energy Density Plasma Science, Warm Dense Matter

The quantum equations of state of plasma under the influence of a weak magnetic field

N. A. Hussein, D. A. Eisa, and M. G. Eldin

Phys. Plasmas 19, 052701 (2012); http://dx.doi.org/10.1063/1.4704794 (6 pages)

Online Publication Date: 9 May 2012

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The aim of this paper is to calculate the magnetic quantum equations of state of plasma, the calculation is based on the magnetic binary Slater sum in the case of low density. We consider only the thermal equilibrium plasma in the case of nλab3≪1, where λab2 = math is the thermal De Broglie wave length between two particles. The formulas contain the contributions of the magnetic field effects. Using these results we compute the magnetization and the magnetic susceptibility. Our equation of state is compared with others.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
05.70.Ce Thermodynamic functions and equations of state

Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry

J. T. Cassibry, M. Stanic, S. C. Hsu, F. D. Witherspoon, and S. I. Abarzhi

Phys. Plasmas 19, 052702 (2012); http://dx.doi.org/10.1063/1.4714606 (9 pages)

Online Publication Date: 14 May 2012

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We have performed three-dimensional (3D) simulations using smoothed particle hydrodynamics (SPH) in order to study the effects of discrete plasma jets on the processes of plasma liner formation, implosion on vacuum, and expansion. It was found that the pressure histories of the inner portion of the liner from 3D SPH simulations with a uniform liner and with 30 discrete plasma jets were qualitatively and quantitatively similar from peak compression through the complete stagnation of the liner. The 3D simulations with a uniform liner were first benchmarked against results from one-dimensional radiation-hydrodynamic simulations [T. J. Awe et al., Phys. Plasmas 18, 072705 (2011)]. Two-dimensional plots of the pressure field show that the discrete jet SPH case evolves towards a profile that is almost indistinguishable from the SPH case with a uniform liner, thus indicating that non-uniformities due to discrete jets are smeared out by late stages of the implosion. The processes of plasma liner formation and implosion on vacuum were shown to be robust against Rayleigh-Taylor instability growth. Finally, interparticle mixing for a liner imploding on vacuum was investigated. The mixing rate was found to be very small until after the peak compression for the 30 jet simulations.
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52.75.-d Plasma devices
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.-y Plasma simulation
back to top Ionospheric, Solar-System, and Astrophysical Plasmas

Orbital ferromagnetism and the Chandrasekhar mass-limit

M. Akbari-Moghanjoughi

Phys. Plasmas 19, 052901 (2012); http://dx.doi.org/10.1063/1.4714611 (7 pages)

Online Publication Date: 15 May 2012

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In this paper, we use quantum magnetohydrodynamic as well as magnetohydrostatic (MHS) models for a zero-temperature Fermi-Dirac plasma to show the fundamental role of Landau orbital ferromagnetism (LOFER) on the magnetohydrostatic stability of compact stars. It is revealed that the generalized flux-conserved equation of state of form B = βρ2s/3 only with conditions 0 ≤ s ≤ 1 and 0 ≤ β<math can lead to a stable compact stellar configuration. The distinct critical value βcr = math is shown to affect the magnetohydrostatic stability of the LOFER (s = 1) state and the magnetic field strength limit on the compact stellar configuration. Furthermore, the value of the parameter β is remarked to fundamentally alter the Chandrasekhar mass-radius relation and the known mass-limit on white dwarfs when the star is in LOFER state. Current findings can help to understand the role of flux-frozen ferromagnetism and its fundamental role on hydrostatic stability of relativistically degenerate super-dense plasmas such as white dwarfs.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
95.30.Qd Magnetohydrodynamics and plasmas
97.10.Ld Magnetic and electric fields; polarization of starlight
97.20.Rp Faint blue stars (including blue stragglers), white dwarfs, degenerate stars, nuclei of planetary nebulae
52.27.Ny Relativistic plasmas
back to top Lasers, Particle Beams, Accelerators, Radiation Generation

Quasi-matched propagation of ultra-short, intense laser pulses in plasma channels

C. Benedetti, C. B. Schroeder, E. Esarey, and W. P. Leemans

Phys. Plasmas 19, 053101 (2012); http://dx.doi.org/10.1063/1.4707393 (8 pages)

Online Publication Date: 4 May 2012

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The propagation of an ultrashort and relativistically intense laser pulse in a preformed plasma channel is investigated. The nonlinear paraxial wave equation describing the laser propagation in the plasma is solved both analytically and numerically. For any arbitrary temporal laser pulse profile with a given power (less then the critical power for self-focusing) and any prescribed transverse density profile in the channel, we determine the laser intensity distribution along the pulse ensuring quasi-matched propagation, neglecting non-paraxial effects. For the case of a Gaussian laser with an initially uniform spot throughout the pulse, we determine the optimal channel depth that minimizes laser evolution (e.g., minimizes spot size oscillations). The analytical and semi-analytical results obtained for both cases in the weakly relativistic regime are presented and validated through comparison with numerical simulations.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.27.Ny Relativistic plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.-y Plasma simulation
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.60.Cb Numerical simulation; solution of equations

Frequency-selective plasmonic wave propagation through the overmoded waveguide with photonic-band-gap slab arrays

Young-Min Shin

Phys. Plasmas 19, 053102 (2012); http://dx.doi.org/10.1063/1.4707394 (5 pages)

Online Publication Date: 10 May 2012

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Confined propagation of guided waves through the periodically corrugated channel sandwiched between two staggered dielectric photonic-band-gap slab arrays is investigated with the band-response analysis. Numerical simulations show that longitudinally polarized evanescent waves within the band gap propagate with insertion loss of ∼−0.2 to 1 dB (−0.05 to 0.4 dB/mm at G-band) in the hybrid band filter. This structure significantly suppresses low energy modes and higher-order-modes beyond the band-gap, including background noises, down to ∼−45 dB. This would enable the single-mode propagation in the heavily over-moded waveguide (TEM-type), minimizing abnormal excitation probability of trapped modes. This band filter could be integrated with active and passive RF components for electron beam and optoelectronic devices.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.65.-y Plasma simulation
52.25.Mq Dielectric properties
42.70.Qs Photonic bandgap materials
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
02.60.Cb Numerical simulation; solution of equations

Effect of pulse profile and chirp on a laser wakefield generation

Xiaomei Zhang, Baifei Shen, Liangliang Ji, Wenpeng Wang, Jiancai Xu, Yahong Yu, Longqing Yi, Xiaofeng Wang, Nasr A. M. Hafz, and V. Kulagin

Phys. Plasmas 19, 053103 (2012); http://dx.doi.org/10.1063/1.4714610 (7 pages)

Online Publication Date: 10 May 2012

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A laser wakefield driven by an asymmetric laser pulse with/without chirp is investigated analytically and through two-dimensional particle-in-cell simulations. For a laser pulse with an appropriate pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced by using an asymmetric un-chirped laser pulse with a fast rise time; however, the growth is small. On the other hand, the wakefield can be greatly enhanced for both positively chirped laser pulse having a fast rise time and negatively chirped laser pulse having a slow rise time. Simulations show that at the early laser-plasma interaction stage, due to the influence of the fast rise time the wakefield driven by the positively chirped laser pulse is more intense than that driven by the negatively chirped laser pulse, which is in good agreement with analytical results. At a later time, since the laser pulse with positive chirp exhibits opposite evolution to the one with negative chirp when propagating in plasma, the wakefield in the latter case grows more intensely. These effects should be useful in laser wakefield acceleration experiments operating at low plasma densities.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Rr Particle-in-cell method
52.25.Fi Transport properties

A study of fast electron energy transport in relativistically intense laser-plasma interactions with large density scalelengths

R. H. H. Scott, F. Perez, J. J. Santos, C. P. Ridgers, J. R. Davies, K. L. Lancaster, S. D. Baton, Ph. Nicolai, R. M. G. M. Trines, A. R. Bell, S. Hulin, M. Tzoufras, S. J. Rose, and P. A. Norreys

Phys. Plasmas 19, 053104 (2012); http://dx.doi.org/10.1063/1.4714615 (13 pages)

Online Publication Date: 15 May 2012

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A systematic experimental and computational investigation of the effects of three well characterized density scalelengths on fast electron energy transport in ultra-intense laser-solid interactions has been performed. Experimental evidence is presented which shows that, when the density scalelength is sufficiently large, the fast electron beam entering the solid-density plasma is best described by two distinct populations: those accelerated within the coronal plasma (the fast electron pre-beam) and those accelerated near or at the critical density surface (the fast electron main-beam). The former has considerably lower divergence and higher temperature than that of the main-beam with a half-angle of ∼20°. It contains up to 30% of the total fast electron energy absorbed into the target. The number, kinetic energy, and total energy of the fast electrons in the pre-beam are increased by an increase in density scalelength. With larger density scalelengths, the fast electrons heat a smaller cross sectional area of the target, causing the thinnest targets to reach significantly higher rear surface temperatures. Modelling indicates that the enhanced fast electron pre-beam associated with the large density scalelength interaction generates a magnetic field within the target of sufficient magnitude to partially collimate the subsequent, more divergent, fast electron main-beam.
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52.25.Fi Transport properties
52.27.Ny Relativistic plasmas
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Gj Plasma heating by particle beams
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Highly efficient accelerator of dense matter using laser-induced cavity pressure acceleration

J. Badziak, S. Jabłoński, T. Pisarczyk, P. Rączka, E. Krousky, R. Liska, M. Kucharik, T. Chodukowski, Z. Kalinowska, P. Parys, M. Rosiński, S. Borodziuk, and J. Ullschmied

Phys. Plasmas 19, 053105 (2012); http://dx.doi.org/10.1063/1.4714660 (8 pages)

Online Publication Date: 15 May 2012

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Acceleration of dense matter to high velocities is of high importance for high energy density physics, inertial confinement fusion, or space research. The acceleration schemes employed so far are capable of accelerating dense microprojectiles to velocities approaching 1000 km/s; however, the energetic efficiency of acceleration is low. Here, we propose and demonstrate a highly efficient scheme of acceleration of dense matter in which a projectile placed in a cavity is irradiated by a laser beam introduced into the cavity through a hole and then accelerated in a guiding channel by the pressure of a hot plasma produced in the cavity by the laser beam or by the photon pressure of the ultra-intense laser radiation trapped in the cavity. We show that the acceleration efficiency in this scheme can be much higher than that achieved so far and that sub-relativisitic projectile velocities are feasible in the radiation pressure regime.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.Fi Transport properties
52.27.Ny Relativistic plasmas
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Acceleration of cone-produced electrons by double-line Ti-sapphire laser beating

Y. Mori and Y. Kitagawa

Phys. Plasmas 19, 053106 (2012); http://dx.doi.org/10.1063/1.4707390 (6 pages)

Online Publication Date: 16 May 2012

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Acceleration of electrons is demonstrated in a beat wave scheme by using a prepulse-free short-pulse (150 fs) double-line Ti-sapphire laser. To inject electrons, we used a hybrid target composed of a cone-drilled plate and a gas jet, where the cone-produced electrons were accelerated via the forced plasma wave excited in the gas jet that was situated behind the plate. This resulted in an increase in slope temperature from 0.05 to 0.15 MeV. We find a correlation between the slope temperature and forced relativistic plasma wave. The wake amplitude is 15 GV/m at the resonant density of 2.5×1018 cm-3 in a hydrogen plasma. The wake acceleration models can explain the increase in slope temperature.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.75.-d Plasma devices
52.27.Ny Relativistic plasmas
52.25.-b Plasma properties

Nonlinear theory for a terahertz gyrotron with a special cross-section interaction cavity

XueSong Yuan (袁学松), Ying Lan (兰颖), Yu Han (韩煜), and Yang Yan (鄢扬)

Phys. Plasmas 19, 053107 (2012); http://dx.doi.org/10.1063/1.4714755 (5 pages)

Online Publication Date: 16 May 2012

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The fully numerical nonlinear theory for a gyrotron with a special cross-section interaction cavity has been developed in this paper. In this theory, the analytical solution to different modes in the special cross-section interaction cavity is replaced by the numerical solution based on electromagnetic simulation results. A 0.4 THz third harmonic gyrotron with an azimuthally corrugated interaction cavity has been investigated by using this theory and simulation results show that this approach has a significant advantage of developing high harmonic terahertz gyrotrons.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations

Laser-driven proton acceleration using a conical nanobrush target

Jinqing Yu (余金清), Zongqing Zhao (赵宗清), Xiaolin Jin (金晓林), Fengjuan Wu (吴凤娟), Yonghong Yan (闫永宏), Weimin Zhou (周维民), Leifeng Cao (曹磊峰), Bin Li (李斌), and Yuqiu Gu (谷渝秋)

Phys. Plasmas 19, 053108 (2012); http://dx.doi.org/10.1063/1.4714809 (4 pages)

Online Publication Date: 16 May 2012

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A conical nanobrush target is proposed to improve the total proton energy-conversion efficiency in proton beam acceleration and investigated by two-dimensional particle-in-cell (2D-PIC) simulations. Results indicate a significant enhancement of the number and energies of hot electrons through the target rear side of the conical nanobrush target. Compared with the plain target, the field increases several times. We observe enhancements of the average proton energy and total laser-proton energy conversion efficiency of 105%. This enhancement is attributed to both nanobrush and conical configurations. The proton beam is well collimated with a divergence angle less than 28°. The proposed target may serve as a new method for increasing laser to proton energy-conversion efficiency.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Rr Particle-in-cell method
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
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