Plasma Physics Reports

Charge neutralization of a short ion bunch passing through a plasma slab is studied by means of numerical simulation. It is shown that a fraction of plasma electrons are trapped by the bunch under the action of the collective charge separation field. The accelerated electrons generated in this process excite beam−plasma instability, thereby violating the trapping conditions. The process of electron trapping is also strongly affected by the high-frequency electric field caused by plasma oscillations at the slab boundaries. It is examined how the degree of charge neutralization depends on the parameters of the bunch and plasma slab.

The Hemisphere Plasma Focus (HSPF) device is a new construction in which the discharge takes place between two concentric hemispherical electrodes. A 2D snow plow model is designed in order to simulate the distributions of the HSPF characteristics between the two electrodes. The model used the momentum and circuit equations to describe the different characteristics in the rundown phase such as; the distributions of the magnetic field, the sheath velocity, the sheath displacement, and the plasma temperature. The results show that the simulated discharge current is in a good agreement with the experimental signal for input charging voltage of 3 kV and helium gas pressure of 0.6 Torr. The peak discharge current is about 42 kA with rise time of about 8.5 μs and the rundown phase is completed at time of about 6.5 μs. The timelines of the current sheath displacement show that the sheath has almost an umbrella shape. As the current sheath is accelerated in θ-direction towards antipodal point, the magnetic field and the plasma temperature are increased and their values are higher as one goes closer to the inner electrode.

Penetration of a heating pulse of quasistationary electromagnetic field into plasma in constant magnetic field directed along its surface was studied. Weakening of electron heat transfer across the magnetic field leads to more efficient heating of electrons near the plasma surface. As a result, the penetration of the field into the plasma decreases, which is accompanied by suppression of the “inverse” skin effect. Inhomogeneous heating of electrons across the magnetic field leads to generation of an electric field strength component orthogonal to both the magnetic field and the direction of temperature gradient. Appearance of the additional field strength component leads to a change in polarization of the reflected pulse. In a sufficiently strong magnetic field, due to suppression of the electron heat flux and less significant effect of the magnetic field on the ion heat flux, a state with large difference of electron and ion temperatures occurs.

The interaction of an additional electron beam with a previously created charged electron plasma of the squeezed state of two counter-propagating superlimiting electron beams in a closed equipotential cavity was studied numerically. The onset of plasma–beam instability in the absence of ions and quasi-linear relaxation is demonstrated. A significant broadening of the EDF towards higher electron energies was established. The considered process can be useful, for example, in electronic traps operating in the electronic string mode and used for generating highly charged ions with their subsequent injection into ion accelerators.

Basic equations for dust structures are formulated that account for the balance of the forces, plasma fluxes, and grain charges with allowance for nonlinearity in the screening of individual grains and possible violation of quasineutrality due to the interaction of collective fields with plasma fluxes. A theory of non-linear drag forces exerted by plasma fluxes on dust grains is developed for moderate drift flux velocities, higher than the mean ion thermal velocity but much lower than the acoustic speed. It is shown that equilibrium dust structures have finite sizes and negative charges and that they can exist only in a certain range of intensities of external fluxes on their surfaces. When there is no additional volume ionization, the size of the structures is determined by the intensity of the external flux. A study is made of a weakly ionized dusty plasma in which the interaction of its components with neutral gas atoms plays a major role. The ion, electron, and dust density distributions, as well as the distributions of the dust grain charges and plasma fluxes, are calculated self-consistently as functions of the distance from the center of a structure.

Charge and energy fluxes onto a nanoparticle under conditions typical of laboratory plasmas are investigated theoretically. Here, by a nanoparticle is meant a grain the size of which is much smaller than both the electron Larmor radius and Debye length and the thermionic emission from which is not limited by the space charge. Under conditions at which thermionic emission plays an important role, the electric potential and temperature T p of a nanoparticle are determined by solving a self-consistent set of equations describing the balance of energy and charge fluxes onto the nanoparticle. It is shown that, when the degree of plasma ionization exceeds a critical level, the potential of the nanoparticle and the energy flux onto it increase with increasing nanoparticle temperature, so that, starting from a certain temperature, the nanoparticle potential becomes positive. The critical degree of ionization starting from which the potential of a nanoparticle is always positive is determined as a function of the plasma density and electron temperature. The nanoparticle temperature T p corresponding to the equilibrium state of a positively charged nanoparticle is found as a function of the electron density for different electron temperatures.