Particle energization in an expanding magnetized relativistic plasma

Using a 21 / 2-dimensional particle-in-cell (PIC) code to simulate the relativistic expansion of a magnetized collisionless plasma into a vacuum, we report a new mechanism in which the magnetic energy is efficiently converted into the directed kinetic energy of a small fraction of surface particles. We study this mechanism for both electron-positron and electron-ion (m(i)/m(e)=100, m(e) is the electron rest mass) plasmas. For the electron-positron case, the pairs can be accelerated to ultrarelativistic energies. For electron-ion plasmas, most of the energy gain goes to the ions.     

磁化等离子体的鞘层结构

采用流体方法数值研究了斜磁场作用下的等离子体鞘层结构.模拟结果显示磁场对鞘层结构有显著的影响,特别是在磁鞘边界附近离子的密度分布产生了明显的变化.分别讨论了离子垂直入射和斜入射两种情况,当离子斜入射进鞘层时,其运动情况要相对复杂一些.在适当的条件下,洛伦兹力的作用使离子在某些区域产生相对聚集,离子密度分布产生波动. 关键词： 鞘层 等离子体 磁场     

Ballooning vortex in a magnetized plasma

The existence of a ballooning solitary vortex in an inhomogeneous plasma immersed in crossed magnetic and gravitational fields is demonstrated.     

Test-ion diffusion in a magnetized plasma

Cross-field transport of barium test ions is studied in a Q-machine plasma. Test particles are produced and tracked in their motion by an optical tagging method. The comparison between the measured tag signal and a simple theoretical simulation yields an evaluation of the ion diffusivity. Diffusion is supported by classical mechanisms. The injection of different noble buffer gases modifies the plasma parameters in such a way that the diffusion remains classical but its magnitude is reduced     

Non-linear coupling in a magnetized plasma

The coupling coefficients for the non-linear interaction between three different waves in a magnetized plasma have been calculated by means of coupled mode theory.     

Electromagnetic emission in a magnetized plasma

We present a theory of emission of electromagnetic waves, in the ordinary and extraordinary modes, in the presence of Langmuir turbulence in a magnetized plasma due to a high frequency nonlinear force. The mechanism of emission considered is the plasma-maser interaction which is essentially an energy up-conversion process. The growth rates of the ordinary and extra-ordinary mode emissions are calculated and the results are compared with those obtained from the direct formulation. The scope of application of the results to radio spectra from solar flares is then stressed.M.C. College, India. College of General Education, Kyushu University, Ropponmatsu, Japan. Gauhati University, India. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 548–562, May, 1994.     

Weak magnetohydrodynamic turbulence of a magnetized plasma

A weak turbulence of the magnetohydrodynamic waves in a strongly magnetized plasma was studied in the case when the plasma pressure is small as compared to the magnetic field pressure. In this case, the principal nonlinear mechanism is the resonance scattering of fast magnetoacoustic and Alfvén waves on slow magnetoacoustic waves. Since the former waves are high-frequency (HF) with respect to the latter, the total number of HF waves in the system is conserved (adiabatic invariant). In the weak turbulence regime, this integral of motion generates a Kolmogorov spectrum with a constant flux of the number of HF waves toward the longwave region. The shortwave region features a Kolmogorov spectrum with a constant energy flux. An exact angular dependence of the turbulence spectra is determined for the wave propagation angles close to the average magnetic field direction.     

Sheath and plasma parameters in a magnetized plasma system

The variation of electron temperature and plasma density in a magnetized N₂ plasma is studied experimentally in presence of a grid placed at the middle of the system. Plasma leaks through the negatively biased grid from the source region into the diffused region. It is observed that the electron temperature increases with the magnetic field in the diffused region whereas it decreases in the source region of the system for a constant grid biasing voltage. Also, investigation is done to see the change of electron temperature with grid biasing voltage for a constant magnetic field. This is accompanied by the study of the variation of sheath structure across the grid for different magnetic field and grid biasing voltage as well. It reveals that with increasing magnetic field and negative grid biasing voltage, the sheath thickness expands.     

New mode of operating a magnetized coaxial plasma gun for injecting magnetic helicity into a spheromak

By operating a magnetized coaxial plasma gun continuously with just sufficient current to enable plasma ejection, large gun-voltage spikes (approximately 1 kV) are produced, giving the highest sustained voltage approximately 500 V and highest sustained helicity injection rate observed in the Sustained Spheromak Physics Experiment. The spheromak magnetic field increases monotonically with time, exhibiting the lowest fluctuation levels observed during formation of any spheromak (B/B>/=2%). The results suggest an important mechanism for field generation by helicity injection, namely, the merging of helicity-carrying filaments.     

Azimuthal surface waves in a magnetized plasma

A theoretical analysis is made of the dispersion properties of surface waves propagating along the azimuth in magnetized cylindrical plasma waveguides. It is shown that surface oscillations of the ion component may propagate in these waveguides. Zh. Tekh. Fiz. 68, 25–28 (December 1998)     

Nonlinear electrostatic waves in a magnetized plasma

The modulational interaction of finite-amplitude high-frequency electrostatic waves propagating at an arbitrary angle to an external magnetic field with slow plasma motion is considered. A set of nonlinear evolution equations describing the interaction is obtained. New types of solitary waves propagating at near sonic speeds are found.     

Solitons in a magnetized relativistic electron-positron plasma

Nonlinear equations for the interaction of the Langmuir wave field and the transverse electromagnetic field in the pulsar magnetosphere are derived. These equations take into account the modulational instability of plasma waves and its decay into two transversal waves.     

Neutrino magnetic moment in a magnetized plasma

The magnetized-plasma contribution to the neutrino anomalous magnetic moment is calculated. It is shown that, in a magnetized plasma, only part of the neutrino additional energy associated with the neutrino spin and with the magnetic-field strength contributes to the neutrino magnetic moment. It is found that, in contrast to results presented previously in the literature, the presence of a magnetized plasma does not lead to a substantial enhancement of the neutrino magnetic moment.     

Diffusion in a strongly coupled magnetized plasma

A first-principles study of diffusion in a strongly coupled one-component plasma in a magnetic field B is presented. As in a weakly coupled plasma, the diffusion coefficient perpendicular to the field exhibits a Bohm-like 1/B behavior in the strong-field limit but its overall scaling is substantially different. The diffusion coefficient parallel to the field is strongly affected by the field as well and also approaches a 1/B scaling, in striking contrast to earlier predictions.     

Spontaneous thermal waves in a magnetized plasma

Coherent temperature oscillations corresponding to thermal (diffusion) waves are observed to be spontaneously excited in a narrow temperature filament embedded in a large, but colder, magnetized plasma. The parallel and transverse propagation properties of the waves satisfy the predictions of the classical transport theory based on Coulomb collisions. The frequency of the oscillations meets the conditions for a quarter-wave thermal resonator. This is the plasma version of thermal resonators used in the study of other states of matter.     

Photon processes in a strongly magnetized plasma

The photon-scattering process γe ^± → γe ^± is considered in strongly magnetized matter at arbitrary values of temperature and an arbitrary chemical potential. Simple expressions for the absorption coefficients in a strongly magnetized plasma are obtained in two limiting cases, that of a rarefied chargesymmetric plasma and that of a degenerate plasma. Astrophysical applications of the results obtained here are discussed.