Large-scale resistive instability of a relativistic electron beam in a plasma channel

The kinetic equation method is used to study the stability of a heavy-current electron beam in a dense plasma channel with a relatively low conductivity. Increments and critical currents are obtained. It is shown that even slightly nonlinear transverse motion stabilizes the system. The main conclusions agree with the experimental results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 84–89, April, 1986.     

Parametric instabilities produced by a relativistic electron beam in a plasma

The parametric instability driven by the primary spectrum of the hydrodynamic two-stream instability produced by a relativistic electron beam in a plasma is investigated. The saturated level of the primary wave electric field is determined by electron trapping in the potential well of the wave or by the quasilinear beam relaxation process. After saturation, the primary wave collapses by way of the oscillating two-stream instability. The cases of the strong and weak primary electric field in comparison with the thermal energy of a plasma are considered. For a strong field the growth rates of the parametric instability and plasma heating due to the latter are found. Ion heating is not significant in comparison with electron heating (approximately as the cube root of the mass ratio). In a weak field the parametric oscillating two-stream spectrum of saturation is found. In the one-dimensional case this spectrum of electric field energy fluctuations varies as k⁻² if the fluctuation field exceeds the threshold pump electric field for the oscillating two-stream instability. For the weak field plasma heating rate is found. Since the energy transfer is via Landau damping, the particle heating is characterized by the formation of high-energy tails on the distribution function.     

Anomalous scattering of a relativistic electron beam in a beam created plasma

Measurements of the velocity angular distribution of a relativistic electron beam (0.8 MV, 6 kA, 150 ns) after propagation through hydrogen gas are presented. At a pressure of 25 Pa scattering of the beam electrons into a preferential angular interval is observed. At 190 Pa anomalously large scattering is observed, up to an angular width of 90°, during about 30 ns.     

Laser-driven relativistic electron dynamics in a cylindrical plasma channel

The energy and trajectory of the electron, which is irradiated by a high-power laser pulse in a cylindrical plasma channel with a uniform positive charge and a uniform negative current, have been analyzed in terms of a single-electron model of direct laser acceleration. We find that the energy and trajectory of the electron strongly depend on the positive charge density, the negative current density, and the intensity of the laser pulse. The electron can be accelerated significantly only when the positive charge density, the negative current density, and the intensity of the laser pulse are in suitable ranges due to the dephasing rate between the wave and electron motion. Particularly, when their values satisfy a critical condition,the electron can stay in phase with the laser and gain the largest energy from the laser. With the enhancement of the electron energy, strong modulations of the relativistic factor cause a considerable enhancement of the electron transverse oscillations across the channel, which makes the electron trajectory become essentially three-dimensional, even if it is flat at the early stage of the acceleration.     

Calculation of the interaction force between a relativistic electron beam and an Ohmic plasma channel

A formula for calculating the interaction force between a relativistic electron beam and a preformed Ohmic plasma channel with an arbitrary offset of the channel axis from the beam axis is obtained in the case of complete charge neutralization. It is shown that this force is repulsive for radial profiles of the conductivity with a peak on the channel axis. Zh. Tekh. Fiz. 67, 69–76 (June 1997)     

Calculation of force exerted by the Ohmic plasma channel on a relativistic electron beam propagating in a dense gas-plasma medium

The problem on the interaction of an Ohmic plasma channel displaced in the transverse direction with a paraxial azimuthally symmetric relativistic electron beam propagating in a dense gas-plasma medium is considered. The formula for determining the force of the beam-plasma interaction is derived using the “hard” model of the beam and the channel in the case of an arbitrary displacement of the symmetry axis of the plasma channel relative to the corresponding axis of the beam. The forces are calculated in the Bennett and Gauss approximations for the radial profiles of the beam and the channel.     

Estimation of the longitudinal electric field produced by a relativistic electron beam in a plasma

An axially symmetric model is used to analytically estimate the longitudinal electric field created in a plasma by an injected electron beam. The relationship can be used to estimate the electron beam energy loss in the range of parameters where theoretical studies rely only on numerical simulations. The results are of interest for creating relativistic electron beams, studying their relaxation in plasma, and developing new methods for charged particle acceleration.     

Effect of the parameters of the plasma channel produced by a high-current relativistic electron beam in dense gaseous media on the beam transportation stability

Results are presented from experimental studies of the time evolution of the plasma channel produced by a high-current electron beam (with an electron energy of E _e = 1.1 MeV, a beam current of I _b = 24 kA, and a pulse duration of t = 60 ns) in helium, nitrogen, neon, air, argon, krypton, xenon, and humid air (air: H₂O) at pressures from 1 to 760 Torr. It is shown that, in gases characterized by a small ratio of the collision frequency to the gas ionization rate u _i , the electron beam produces a broad high-conductivity plasma channel, such that R _b/R _p < 1, where R _b and R _p are the beam and channel radii, respectively. As a result, large-scale resistive hose instability is suppressed.     

相对论电子束在动态加载等离子体中的自聚焦传输

为了进一步研究相对论电子束-离子通道辐射实验和理论的需要, 研究了相对论电子束入射中性气体以及通过碰撞电离动态加载等离子体实现对高能束流的自聚焦传输过程PIC(particle in cell) 模拟发现, 电子束电离出的离子背景能够实现对电子束的聚焦传输. 但是离子背景横向和纵向的不均匀性对束流的传输特性有显著影响. 在此基础之上, 提出了电子束在横向不均匀离子背景中传输的理论模型, 给出了束流的自聚焦条件.数值计算结果表明, 横向不均匀性会导致电子束的混合相位传输, 使得焦点附近内层电子可能跑到电子束外而被散焦损失, 这与PIC模拟的结果相符. 此外, PIC模拟还发现, 由于电子束的自聚焦, 在焦点处将电离出更多的离子而引起纵向不均匀性, 纵向不均匀性使得碰撞后的低能电子被俘获, 俘获电子效应会大幅降低电子束的传输效率. 但是俘获电子在纵向呈准周期分布, 对传输电子起到静电Wiggler场的作用, 可能实现静电Wiggler场的动态加载. 研究结果对于进一步研究电子束-等离子体系统的实验以及理论模型提出有一定的参考价值.     

Inhomogeneous relativistic electron beam interaction with inhomogeneous warm plasma

The interaction of inhomogeneous relativistic electron beam with inhomogeneous bounded warm plasma, which leads to amplification of waves, is analyzed. It is shown that due to the resonant increase in wave’s field with a decrease in the plasma permittivity to zero, the power absorbed by plasma is finite and depends on the plasma thermal velocity. The relativistic electron beam not only amplifies waves in plasma but also provides efficient absorption of these waves by plasma.     

Ion-focused propagation of a relativistic electron beam in the self-generated plasma in atmosphere

It is known that ion-focused regime (IFR) can effectively suppress expansion of a relativistic electron beam (REB). Using the particle-in-cell Monte Carlo collision (PIC-MCC) method, we numerically investigate the propagation of an REB in neutral gas. The results demonstrate that the beam body is charge neutralization and a stable IFR can be established. As a result, the beam transverse dimensions and longitudinal velocities keep close to the initial parameters. We also calculate the charge and current neutralization factors of the REB. Combined with envelope equations, we obtain the variations of beam envelopes, which agree well with the PIC simulations. However, both the energy loss and instabilities of the REB may lead to a low transport efficiency during long-range propagation. It is proved that decreasing the initial pulse length of the REB can avoid the influence of electron avalanche. Using parts of REB pulses to build a long-distance IFR in advance can improve the beam quality of subsequent pulses. Further, a long-distance IFR may contribute to the implementation of long-range propagation of the REB in space environment.     

Hardening of steel by alloying in a relativistic electron beam

The possibility was demonstrated of hardening a steel surface layer by alloying it using the energy of relativistic electrons. Investigations were made of how the structure, hardness, and depth of the hardened layer depend on the processing regime and on the initial temperature of the steel in the case of alloying with boron carbide and with Cr+C and Cr+B₄C mixtures. The greatest hardening was achieved by alloying with a mixture of Cr and B₄C powders. This was due to a higher volume fraction of the second phase in the layer and to the precipitation of chromium carboborides. Several types of alloying utilizing Cr+B₄C and containing additional agents and modifiers were developed on the basis of the data obtained.Institute of Hardening Physics and Materials Research, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 57–63, March, 1993.