Nonlinear Right-Hand Polarized Wave in Plasma in the Electron Cyclotron Resonance Region

The propagation of a nonlinear right-hand polarized wave along an external magnetic field in subcritical plasma in the electron cyclotron resonance region is studied using numerical simulations. It is shown that a small-amplitude plasma wave excited in low-density plasma is unstable against modulation instability with a modulation period equal to the wavelength of the excited wave. The modulation amplitude in this case increases with decreasing detuning from the resonance frequency. The simulations have shown that, for large-amplitude waves of the laser frequency range propagating in plasma in a superstrong magnetic field, the maximum amplitude of the excited longitudinal electric field increases with the increasing external magnetic field and can reach 30% of the initial amplitude of the electric field in the laser wave. In this case, the energy of plasma electrons begins to substantially increase already at magnetic fields significantly lower than the resonance value. The laser energy transferred to plasma electrons in a strong external magnetic field is found to increase severalfold compared to that in isotropic plasma. It is shown that this mechanism of laser radiation absorption depends only slightly on the electron temperature.     

Excitation of magnetic fields by a circularly polarized laser pulse in a plasma channel

The excitation of quasistatic magnetic fields by a circularly polarized laser pulse in a plasma channel is considered. It is shown that, to second order in the amplitude of the electric field of the laser pulse, circular rotation of the plane of polarization of the laser radiation in a radially nonuniform plasma gives rise to a nonlinear azimuthal current and leads to the excitation of the radial and axial components of the magnetic field. The dependence of the magnetic field distribution over the plasma channel on the spatial dimensions of the pulse and on the channel width is investigated for a moderate-power laser pulse. The structure of the magnetic fields excited by a relativistic laser pulse in a wide plasma channel is analyzed.     

Role of the Hall flute instability in the interaction of laser and space plasmas with a magnetic field

The interaction of an expanding laser plasma with a uniform external magnetic field is studied over a wide range of experimental parameters (for a plasma energy of up to 300 J and a magnetic induction of up to 8 kG). By analyzing the data from these and other experiments, as well as the results of simulations with the use of a two-fluid Hall plasma model, it was found for the first time that the flute instability of the plasma boundary plays a decisive role in the process of the plasma cloud expansion. It is shown that, when the ion Larmor radius is sufficiently large, this instability can significantly affect the maximum radius of the diamagnetic cavity of the plasma cloud and the deceleration of its front by the magnetic field. A physical model based on the Hall effect is proposed to explain such influence. The model adequately describes data from one-dimensional simulations, as well as from experiments with quasi-spherical laser plasma clouds. The results obtained can be helpful in interpreting the data from active magnetospheric experiments with barium plasma clouds (such as AMPTE) and analyzing the plasma dynamics in future ICF reactors and propulsion systems with a magnetic field for direct conversion of fusion energy into electric energy.     

Magneto-inertial fusion with laser compression of a magnetized spherical target

The paper is devoted to the principles of magneto-inertial fusion and laser-plasma methods of generation of a Megagauss field during spherical implosion of a magnetized target. A model based on a magnetic confinement system, namely, a cusp configuration with inertial compression of the target by a laser driver, is developed. The dynamics of plasma in a cusp compressed under the effect of laser beams is precalculated. Analytical and numerical estimates of the particle number and magnetic field intensity during magneto-inertial plasma compression are obtained. The problems of irradiation of a spherically closed volume by a high-energy laser pulse are discussed.     

Ion acceleration in a dipole vortex in a laser plasma corona

Particle-in-cell simulations show that the inhomogeneity scale of the plasma produced in the interaction of high-power laser radiation with gas targets is of fundamental importance for ion acceleration. In a plasma slab with sharp boundaries, the quasistatic magnetic field and the associated electron vortex structure produced by fast electron beams both expand along the slab boundary in a direction perpendicular to the plasma density gradient, forming an extended region with a quasistatic electric field, in which the ions are accelerated. In a plasma with a smooth density distribution, the dipole magnetic field can propagate toward the lower plasma density in the propagation direction of the laser pulse. In this case, the electron density in an electric current filament at the axis of the magnetic dipole decreases to values at which the charge quasineutrality condition fails to hold. In electric fields generated by this process, the ions are accelerated to energies substantially higher than those characteristic of plasma configurations with sharp boundaries.     

Raman scattering of laser radiation in magnetoactive plasma

Raman scattering in a subcritical plasma is simulated numerically for the case where the laser radiation propagates transversely to an external magnetic field. It is shown that, in the linear stage of Raman instability, the magnetic field decreases the instability growth rate for forward scattering and increases it for backward scattering. As the value of the magnetic field increases, the stochastic heating of plasma electrons is enhanced in the region of backscattering.     

Parametric Interaction of High-Power Laser Radiation with Plasma in a Strong Magnetic Field

Plasma Physics Reports - The article deals with interaction of an extraordinary laser wave of high amplitude with inhomogeneous plasma in a strong magnetic field in the vicinity of twice the...     

Mechanism of erythrocyte aggregate formation in presence of magnetic field and dextrans as analyzed by laser light scattering

The mechanism of erythrocyte aggregation has been studied in normal plasma, dextran 40 and dextran 70 suspensions in presence and absence of magnetic field at a concentration of 5 percent by laser light scattering. The inhomogeneous magnetic field enhances the aggregating tendency of normal erythrocytes. The growth of aggregates due to dextran 70 is enhanced in presence of magnetic field. On the other hand the disaggregating effect of dextran 40 is reduced due to this field. The induced changes due to magnetic field during the development of erythrocyte aggregates in these media are determined.     

Study of the glow dynamics in a laser-produced plasma jet expanding across the magnetic field

Results are presented from experimental studies of the glow dynamics of a plasma jet generated during the irradiation of a plane aluminum target by an iodine laser pulse with the wavelength 1.315 μm. The laser pulse energy was 330–480 J, the pulse duration was 0.5 ns, and the focal spot diameter was 3 mm, the laser intensity on the target surface being ∼10¹³ W/cm². The jet expanded across an external magnetic field with the strength ∼1 kOe. The residual air pressure in the vacuum chamber was ∼10⁻⁵ Torr. The spatiotemporal behavior of the jet glow was investigated using a nine-frame camera in two mutually perpendicular directions (along and across the magnetic field). The results of measurements indicate azimuthal asymmetry of the jet expansion.     

On the theory of Cherenkov emission from a short laser pulse in a magnetized plasma

Cherenkov emission from a short laser pulse propagating in an underdense plasma along a constant magnetic field is considered. The spectral, angular, energy, and spatiotemporal parameters of the emitted radiation are investigated. It is shown that the spectral content of the radiation and its directionality depend sensitively on the plasma and laser-pulse parameters. For instance, the most intense backward radiation at the upper hybrid frequency is generated by a tightly focused laser pulse.     

Heating of Plasma Electrons by Laser Radiation under Parametric Resonance Conditions in Strong Magnetic Field

Plasma Physics Reports - Heating of plasma electrons by an extraordinary laser wave at the double upper hybrid frequency in a strong magnetic field is studied numerically by the particle-in-cell...     

High-power terahertz optically pumped NH3 laser for plasma diagnostics

The parameter of a terahertz (THz) laser intended for plasma diagnostics in electrodynamic accelerators and tokamaks with a strong magnetic field are discussed. Generation of THz radiation in an ammonia laser under the action of high-power pulsed optical pumping by the radiation of a 10P(32) CO₂ laser is simulated numerically. The main characteristics of the output radiation, such as its spectrum, peak intensity, time dependence, and total energy, are calculated.     

Generation of strong magnetic fields by counterpropagating moderate-intensity laser pulses in a low-density plasma

A study is made of the generation of strong quasistatic magnetic fields by counterpropagating moderate-intensity laser pulses of different frequencies in a low-density plasma. Strong magnetic fields are generated by small-scale large-amplitude plasma waves excited at different frequencies by ponderomotive forces in the interaction region of laser pulses. It is shown that magnetic fields are generated most efficiently under resonance conditions such that the frequency difference between laser pulses coincides with the plasma frequency. The spatial distribution of quasistatic magnetic fields is investigated, and the pattern of the contour lines of the electric current is calculated.     

Effect of the magnetic field on the resonant particle acceleration

The acceleration of charged particles trapped by a potential wave in a magnetic field is investigated as applied to the problem of the generation of fast particles in a laser plasma. The conditions for unlimited particle acceleration are determined, and the spectra of fast particles are found.     

Decay instability of a laser pulse propagating in a transverse direction in a magnetized plasma

The decay instability of a lser pulse propagating across an external magnetic field in a subscritical plasma is investigated analytically and numerically. It is shown that, when the relaxation of the pulse is taken into account, the hydrodynamic growth rate of the decay instability is slower than that obtained earlier in the constant-amplitude pump wave approximation. The results of numerical simulations by a particle-in-cell method demonstrate that an increase in the amplitude of the parametrically excited waves is accompanied by a decrease in their group velocity; in this case, up to 85% of the laser energy is converted into the energy of the plasma particles. It is found that, under resonance conditions, the magnetic field acts to increase the energy of the accelerated ions that escape from the plasma slab through its front boundary.     

Effects of a homogeneous magnetic field on erythrocyte sedimentation and aggregation

Effects of a homogeneous static magnetic field on erythrocyte sedimentation rate (ESR) have been assessed by using the standard Westergren method. A magnetic field of 6.3 T in the vertical direction only slightly enhanced ESR in saline solution, which was consistent with an effect on cell orientation. On the other hand, the magnetic field greatly enhanced ESR in plasma. It took a long time (about 20 min) for an ESR change to occur in plasma in response to the magnetic field. The effects in plasma were too large to originate only from cell orientation and were clearly distinct from a magnetic field-induced Boycott effect under an inhomogeneous magnetic field. A morphological examination and the nonlinear time course of the sedimentation in plasma indicated that the magnetic field increased cell aggregation and thereby enhanced ESR in plasma. Bioelectromagnetics 18:215–222, 1997. © 1997 Wiley-Liss, Inc.     

Optical properties of a plasma produced by the tunneling ionization of atoms of a matter in the field of a circularly polarized wave

General features of the absorption and reflection of a test wave by a nonequilibrium plasma produced in the tunneling ionization of atoms of a matter by a circularly polarized laser pulse are described. Because of the highly anisotropic distribution of photoelectrons, the optical properties of a nonequilibrium plasma differ considerably from those of a plasma with a Maxwellian electron velocity distribution. Physically, an anomalous behavior of the absorption coefficient and of the phase shift stems from the fact that electron kinetics in the skin layer is modified by the alternating magnetic field of the test wave.     

Characterization of 1064 nm Nd:YAG laser-produced cu plasma

The plasma was produced by focusing Nd:YAG laser pulses of 1064 nm wavelength on to a copper target at laser fluences of 5.35, 6.95, and 9.33 J/cm². An ion collector placed along the target surface normal was used to record the time-of-flight (TOF) ion signal during plasma expansion in vacuum. The TOF ion pulses were deconvoluted using the Coulomb-Boltzmann-shifted function to estimate the available Cu ion charge states, equivalent plasma ion temperature, and accelerating potential in the nonequilibrium plasma. The maximum available ion charge state, equivalent plasma ion temperature, and accelerating potential are found to increase with laser fluence. In the local thermal equilibrium conditions, the accelerating potential can be supposed to apply across a distance of the order of the Debye length. The Debye length and, hence, the electric field in the laser produced plasma at three laser fluences values were estimated. The electric field was in the range of 1 MV/cm and increased with laser fluence. In the laser fluence range used in this work, the sum of thermal and adiabatic energy of the ion was slightly higher than its Coulomb energy.     

Structure of the controlled halo-current magnetic field in the T-10 tokamak

In the T-10 tokamak, the magnetic field spatially resonant with a helical MHD perturbation is generated using the controlled halo current supplied using a contact method in the scrape-off-layer plasma. This paper is concerned with studying the spatial structure of the halo current and its magnetic field. For this purpose, the magnetic field of the halo current was measured in one of the cross sections of the torus near the tokamak vacuum vessel wall. The spatial distribution of the magnetic field as a function of the halo current configuration was calculated in the cylindrical approximation. The terms proportional to the plasma pressure were disregarded. The configuration of the halo current and the spatial structure of its magnetic field were determined by comparing the calculated and experimental results.     

Magnetohydrodynamics of a weakly ionized plasma: Ambipolar magnetic diffusion and shock front structure

Kinetic equations with the BGK collision integral are used to derive MHD equations for a weakly ionized plasma that are applicable over a broad range of magnetic field strengths. In strong magnetic fields, a substantial contribution to the transverse diffusion of the magnetic field comes from the ambipolar magnetic diffusion, which is associated with the motion of both the charged component and the magnetic field against the background of the neutral plasma component. The problems of the magnetic field diffusion in a weakly ionized plasma and the shock wave structure are solved.