Hasil untuk "physics.plasm-ph"

Michael Bonitz, Anatoly Zagorodny

Yuri L'vovich Klimontovich (28.09.1924--26.10.2002) was an outstanding theoretical physicist who made major contributions to kinetic theory. On the occasion of his 100th birthday we recall his main scientific achievements.

M. J. Garland, J. C. Wood, G. Boyle et al.

Carefully engineered, controlled, and diagnosed plasma sources are a key ingredient in mastering plasma-based particle accelerator technology. This work reviews basic physics concepts, common types of plasma sources, and available diagnostic techniques to provide a starting point for advanced research into this field.

Brigitte Cros

Relativistic electrons are easily generated by self-injection when an intense laser drives a wakefield in a plasma, giving rise to wide electron energy distributions. Several mechanisms involving additional laser beams or different gas composition or distribution can be used to improve the electron beam quality. These mechanisms are introduced and discussed in the perspective of using laser driven electron sources as injectors for plasma accelerators.

Daniel Gordon, Bahman Hafizi

An exact momentum update useful for particle codes was previously given. The expressions involved were unwieldy. By treating the momentum as a representation of SU(2)xSU(2) instead of SO(3,1), a more compact expression for the exact momentum update is obtained. An expansion in powers of the timestep can be formulated such that invariance properties are exactly preserved, and push rates comparable to the standard Boris pusher are obtained.

Takashi Shiroto, Akinobu Matsuyama, Nobuyuki Aiba

A hyperbolic system must have a set of linearly independent eigenvectors and corresponding real eigenvalues. In numerical simulations, however, the eigenvalues can be complex because truncation errors pollute a characteristic polynomial of the hyperbolic system. Here we propose an eigenstructure-preserving scheme which always generates the real eigenvalues, even in discrete level. Although the eigenstructure is discussed in a non-conservative formulation, the proposed scheme is locally conservative owing to the skew-symmetric operators.

Aleksandr Friman

A technique of magnetized plasma simulation have been implemented into a well known FDTD solver MEEP as a child class of "susceptibility" class. Magnetized plasma posses gyrotrophic properties, polarization vector is being rotated while the wave propagates through the material. Solid state plasma can be found in semiconductor materials which rises a question of using gyrotrophic properties of plasma in modern photonic development. To test the software, a circular polarized wave propagation through 9mm layer of magnetized plasma has been simulated and compared to the analytical solution.

J. Faure

Plasma injection schemes are crucial for producing high-quality electron beams in laser-plasma accelerators. This article introduces the general concepts of plasma injection. First, a Hamiltonian model for particle trapping and acceleration in plasma waves is introduced; ionization injection and colliding-pulse injection are described in the framework of this Hamiltonian model. We then proceed to consider injection in plasma density gradients.

Vladimir Baryshevsky, Alexandra Gurinovich, Evgeny Gurnevich et al.

Triode reflex geometry vircator operating within 3.0 - 4.2 GHz range with efficiency up to 6% is developed and experimentally investigated. Shiftable reflectors are shown to enable frequency tuning and output power control. Radiation frequency and power are analyzed for different cathode-anode gap values and varied reflector positions.

G. Stellmacher, E. Wiehr

We present the detection of a bubble-like cavity traveling through a quiescent prominence. The H-alpha emission in the cavity is >16 times smaller than in its surroundings. The cavity propagates almost with the phase-velocity of MHD compressive waves. We suggest a disruption of the lateral magnetic stability. The Ca II 8542 spectra indicate a material outflow along the lines of force up to 12 km/s.

Ren-Jie Wang, Yong-Chang Huang

We study the general (2+1)-dimensional Davey-Stewartson (DS) equations with nonlinear and gain terms and acquire explicit solutions through variable separation approach. In particular, we deduce some main novel excitations for the DS equations, and further demonstrate different features of these excitations. More importantly, the similar solutions and excitations can be predicted to exist in other related revolution equations such as nonlinear Schrödinger equation to explain the Bose-Einstein condensation.

V. Prudskikh, Yu. A. Shchekinov

We investigate the efficiency of acceleration of charged dust particles by low-frequency Alfvén waves in nonlinear approximation. We show that the longitudinal acceleration of dust particles is proportional to the square of the soliton amplitude $O(|b_m|^2)$, while the transversal acceleration is of $O(|b_m|)$. In the conditions of the interstellar medium the resulting velocity of dust particles can reach 0.3 to 1 km s$^{-1}$.

Dimitar G. Stoyanov

The elementary processes taking place in the formation of charged particles and their flow in parallel-plane, cylindrical and spherical ionization chambers are considered. On the basis of particles and charges balance a differential equation describing the distribution of current densities in the ionization chamber volume is obtained. As a result of the differential equation solution an analytical form of the current-voltage characteristic of an ionization chamber with homogeneous ionization is obtained. For the parallel-plane case the comparison with experimental data is performed.

Eric G. Blackman, George B. Field

We develop a simple mean field approach to the transport of a passive scalar for which the fundamental equation is a second order differential equation in the transported quantity, not a first order equation. Triple correlations are included, as they must be for any realistic description of turbulence. No correlation time enters the theory, only an eddy turnover time. The approach is simpler than standard approaches which incorporate triple correlations, but more realistic than Gaussian or short correlation time closures which do not. A similar approach has proven useful in magnetohydrodynamics.

Hantao Ji, Stephen Terry, Masaaki Yamada et al.

Clear evidence for a positive correlation is established between the magnitude of magnetic fluctuations in the lower-hybrid frequency range and enhancement of reconnection rates in a well-controlled laboratory plasma. The fluctuations belong to the right-hand polarized whistler wave branch, propagating obliquely to the reconnecting magnetic field, with a phase velocity comparable to the relative drift velocity between electrons and ions. The short coherence length and large variation along the propagation direction indicate their strongly nonlinear nature in three dimensions.

Stanislav Boldyrev, Carl R. Gwinn

Observations of radio signals from distant pulsars provide a valuable tool for investigation of interstellar turbulence. The time-shapes of the signals are the result of pulse broadening by the fluctuating electron density in the interstellar medium. While the scaling of the shapes with the signal frequency is well understood, the observed anomalous scaling with respect to the pulsar distance has remained a puzzle for more than 30 years. We propose a new model for interstellar electron density fluctuations, which explains the observed scaling relations. We suggest that these fluctuations obey Levy statistics rather than Gaussian statistics, as assumed in previous treatments of interstellar scintillations.

A. Y. Potekhin, Yu. A. Shibanov, J. Ventura

We study partially ionized hydrogen plasma at temperatures T = 10^{5.5}-10^{6.5} K and magnetic fields B = 10^{12}-10^{13} G, typical of photospheres of isolated neutron stars. We construct an analytic model of the plasma free energy and derive a generalized Saha equation which is used to obtain the opacities.

S. C. Tiwari

The idea of photonic de Broglie waves is discussed in the context of recent obsrved lines in the helium-hydrogen plasma.

A. M. Ignatov, S. A. Trigger

It is shown that absorption of ions by the dust grain may reduce the effective translational temperature of the dust component below the ambient gas temperature.

Stanislav Boldyrev

We propose a phenomenological theory of strong incompressible magnetohydrodynamic turbulence in the presence of a strong large-scale external magnetic field. We argue that in the inertial range of scales, magnetic-field and velocity-field fluctuations tend to align the directions of their polarizations. However, the perfect alignment cannot be reached, it is precluded by the presence of a constant energy flux over scales. As a consequence, the directions of fluid and magnetic-field fluctuations at each scale $λ$ become effectively aligned within the angle $φ_λ\propto λ^{1/4}$, which leads to scale-dependent depletion of nonlinear interaction and to the field-perpendicular energy spectrum $E(k_{\perp})\propto k_{\perp}^{-3/2}$. Our results may be universal, i.e., independent of the external magnetic field, since small-scale fluctuations locally experience a strong field produced by large-scale eddies.

Swadesh M. Mahajan, Riszard Miklaszewski, Komunela I. Nikol'skaya et al.

It is shown that the connection of sufficiently fast flows with dynamical channels for particle escape in the Solar Corona is rather direct: it depends on their ability to deform (in specific cases to distort) the ambient magnetic field lines to temporarily stretch (shrink, destroy) the closed field lines so that the flow can escape the local region. Using a dissipative two--fluid code in which the flows are treated at par with the currents, we have demonstrated channel creation in a variety of closed--field line structures. This self--induced transparency constitutes the active mode for the formation of the solar wind.