V.I. Karas

Charged particle acceleration by an intense wake-field excited in plasmas by either laser pulse or relativistic electron bunch

The results from theoretical and experimental studies, as well as from 2.5-dimensional (2.5-D) numerical simulation of plasma wake field excitation, by either relativistic electron bunch, laser pulse, and the charged particle wake field acceleration are discussed. The results of these investigations make it possible to evaluate the potentialities of the wake field acceleration method and to analyze whether it can serve as a basis for creating a new generation of devices capable of charged particle accelerating at substantially higher (on the order of two to three magnitudes) rates in comparison with those achievable in classical linear high-frequency (resonant) accelerators.

Interaction of microwave radiation undergoing stochastic phase jumps with plasmas or gases

New types of beam-plasma devices generating intense stochastic microwave radiation in the interaction of electron beams with hybrid plasma waveguides were developed and put into operation at the National Science Center Kharkov Institute of Physics and Technology (Ukraine). The objective of the paper is to discuss the results of theoretical and experimental studies and numerical simulations of the normal and oblique incidence of linearly polarized electromagnetic waves on an interface between a vacuum and an overcritical plasma. The main results of the reported investigations are as follows: (i) for the parameter values under analysis, the transmission coefficient for microwaves with a stochastically jumping phase is one order of magnitude greater than that for a broadband regular electromagnetic wave with the same spectral density; (ii) the electrons are heated most efficiently by obliquely incident waves with a stochastically jumping phase and, in addition, the electron distribution function has a high-energy tail; and (iii) necessary conditions for gas breakdown and for the initiation of a microwave discharge in stochastic fields in a light source are determined. The anomalously large transmission coefficient for microwaves, the anomalous character of the breakdown conditions, the anomalous behavior of microwave gas discharges, and the anomalous nature of collisionless electron heating, are attributed to stochastic jumps in the phase of microwave radiation.

Charged prticle aceleration by an itense ultrashort electromagnetic pulse excited in a plasma by laser radiation or by relativistic electron bunches

A review is given of theoretical and experimental investigations and numerical simulations of the generation of intense electromagnetic fields in accelerators based on collective methods of charged particle acceleration at rates two or three orders of magnitude higher than those in classical resonance accelerators. The conditions are studied under which the excitation of accelerating fields by relativistic electron bunches or intense laser radiation in a plasma is most efficient. Such factors as parametric and modulational processes, the generation of a quasistatic magnetic field, and the acceleration of plasma electrons and ions are investigated in order to determine the optimum conditions for the most efficient acceleration of the driven charged-particle bunches.

Theoretical and experimental investigations of a neutralized ion induction linac for inertial confinement fusion

Abstract Studies of an induction linac for space-charge-neutralized beams, comprising an injector and two induction stages with magnetoinsulating cusps in the a

Low-pressure discharge induced by microwave radiation with a stochastically jumping phase

Results are presented from experimental studies on the unique beam-plasma generator of microwave radiation with a stochastically jumping phase (MWRSJP). To interpret the experimental results, a computer code was developed that allows one to simulate the process of gas ionization by electrons heated in the MWRSJP field and the behavior of plasma particles in such a field. The conditions for ignition and maintenance of a microwave discharge in air by MWRSJP are found both experimentally and theoretically, and the pressure range in which the power required for discharge ignition and maintenance is minimum are determined.

2.5-Dimensional numerical simulation of a high-current ion linear induction accelerator

Results are presented from numerical particle simulations of the transport and acceleration of a high-current tubular ion beam through one to five magnetically insulated accelerating gaps. The ion beam is neutralized by an accompanying electron beam. The possibility of transporting a high-current neutralized ion beam through five cusps is demonstrated. It is shown that the quality of the distribution function of a high-current ion beam at the exit from the accelerator can be substantially improved by optimizing the energy of the neutralizing electron beam. It is also shown that, by injecting additional high-current electron beams into the cusps, the accelerated ion beam can be made more monoenergetic and its divergence can be reduced.

Excitation of Langmuir Oscillations by a Laser Pulse in a Semi-Infinite Dense Plasma

A study is made of the nonlinear mechanism for the excitation of Langmuir waves in a dense plasma by an intense laser pulse with the frequency ω = ωp/2 (where ωp is the electron plasma frequency).

Nonequilibrium electron distribution functions in a semiconductor plasma irradiated with fast ions

A kinetic equation for the electrons scattered by acoustic phonons in a solid is derived, and relationships between power-law asymptotic solutions and the particle and energy fluxes in phase space are established. The dependence of the nonextensivity parameter on the intensity of the particle flow in phase space is determined for a nonequilibrium solid-state plasma with sources and sinks. The formation of a steady-state nonequilibrium electron distribution function in a semiconductor with a source and a sink in phase space is numerically simulated using the Landau and Fokker-Planck collision integrals. The nonequilibrium electron distributions formed in the solid-state plasmas of semiconductors and of a Sb/Cs cathode are studied experimentally. It is shown that, within the electron energy range of 5–100 eV, the electron distribution functions decrease with energy according to a power law.

Dissipation of the Energy of a Fast Charged Particle in a Solid-State Plasma

Results are presented from experimental investigations of mechanisms for the dissipation of the energy of light ions in metal plasmas by using the method of secondary electron emission. It is shown that the coefficient of anisotropy of energy transfer from fast light ions is about 1.7. It is also shown that plasma oscillations excited by an ion significantly influence the production and emission of low-energy electrons, especially in the case of projectile molecular ions.

Acceleration and stability of a high-current ion beam in induction fields

A one-dimensional nonlinear analytic theory of the filamentation instability of a high-current ion beam is formulated. The results of 2.5-dimensional numerical particle-in-cell simulations of acceleration and stability of an annular compensated ion beam (CIB) in a linear induction particle accelerator are presented. It is shown that additional transverse injection of electron beams in magnetically insulated gaps (cusps) improves the quality of the ion-beam distribution function and provides uniform beam acceleration along the accelerator. The CIB filamentation instability in both the presence and the absence of an external magnetic field is considered.