Petr Kulhánek

Particle‐in‐Cell Simulation of Helical Structure Onset in Plasma Fiber with Dust Grains

Fully three dimensional PIC program package for the helical pinch numerical simulation was developed in our department. Both electromagnetic and gravitational interactions are incorporated into the model. Collisions are treated via Monte Carlo methods. The program package enabled to prove the conditions of onset of spiral and helical structures in the pinch.

Particle and field solvers in PM models

A fully three-dimensional Particle Mesh model of the plasma fiber was developed in our department for numerical simulations of the onset of helical modes of the fiber. The tests of the particle and field solvers are described in this paper as well as results of the LIC (Line Integral Convolution) field visualization technique.

Visualization techniques in plasma numerical simulations

Numerical simulations of plasma processes usually yield a huge amount of raw numerical data. Information about electric and magnetic fields and particle positions and velocities can be typically obtained. There are two major ways of elaborating these data. First of them is calledplasma diagnostics. We can calculate average values, variances, correlations of variables, etc. These results may be directly comparable with experiments and serve as the typical quantitative output of plasma simulations. The second possibility is theplasma visualization. The results are qualitative only, but serve as vivid display of phenomena in the plasma followed-up. An experience with visualizing electric and magnetic fields via Line Integral Convolution method is described in the first part of the paper. The LIC method serves for visualization of vector fields in two dimensional section of the three dimensional plasma. The field values can be known only in grid points of three-dimensional grid. The second part of the paper is devoted to the visualization techniques of the charged particle motion. The colour tint can be used for particle’s temperature representation. The motion can be visualized by a trace fading away with the distance from the particle. In this manner the impressive animations of the particle motion can be achieved.

Interruptedz-pinch filamentary structure

The longitudinalz-pinch time evolution study between two conical electrodes was carried out by means of the interferometric and the schlieren methods, the discharge basic parameters′ time development (namely geometry, filamentary structure and electron density) was investigated.

AN ESCAPE OF FAST ELECTRONS FROM A PLASMA CLUSTER IN SUBCRITICAL ELECTRIC FIELD

A behaviour of electrons with high initial thermal velocities in plasma clusters is discussed in the paper. These electrons from the tail of the Maxwell velocity distribution can be accelerated into considerable energies by means of an external electric field. Both numerical and analytical estimates of the energy of the escaping electrons and an estimate of the total energy transferred by the electrons from the cluster are treated in the paper. The calculations are performed for a situation usual in coaxial and rail accelerators of the plasma clusters.

The polarization of the plasma cluster in a rail plasma accelerator

In a rail plasma accelerator a polarization of the plasma cluster can occur. The electrons outrun the ions and so a polarization field arises. Some part of energy from the condenser battery corresponds to this field. Simple relations for the maximum polarization length and the polarization energy are derived under conditions of constant cross section area of the plasma cluster and negligible internal magnetic field.

Notes on the relativistic movement of runaway electrons in parallel electric and magnetic fields

Runaway electrons are a potential threat in many plasma devices. At high velocities, the plasma acceleration is not further offset by collisions in the plasma, as in the ohmic regime. The particles obtain relativistic velocity and considerable energy. A typical configuration includes parallel electric and magnetic fields, in which there are no drifts, and the movement of the charged particles is a combination of gyration motion with the acceleration in an electric field. It follows from the Lorentz equation of motion that the transverse velocity component (perpendicular to the fields) will be interconnected with the longitudinal component via the Lorentz factor. The increasing longitudinal velocity will therefore ultimately reduce the magnitude of the transverse velocity component, thereby decreasing the gyrofrequency. The corresponding change in Larmor radius will be offset by the increase in the particle mass and the Larmor radius of gyration therefore remains unchanged. We derive analytical relations f...

Analysis of the instability growth rate during the jet– background interaction in a magnetic field

The two-stream instability is common, responsible for many observed phenomena in nature, especially the interaction of jets of various origins with the background plasma (e.g. extragalactic jet interacting with the cosmic background). The dispersion relation that does not consider magnetic fields is described by the well-known Buneman relation. In 2011, Bohata, Břeň and Kulhanek derived the relation for the two-stream instability without the cold limit, with the general orientation of a magnetic field, and arbitrary stream directions. The maximum value of the imaginary part of the individual dispersion branches ω n (k) is of interest from a physical point of view. It represents the instability growth rate which is responsible for the onset of turbulence mode and subsequent reconnection on the scale of the ion radius accompanied by a strong plasma thermalization. The paper presented here is focused on the non-relativistic instability growth rate and its dependence on various input parameters, such as magnitude and direction of magnetic field, sound velocity, plasma frequency of the jet and direction of the wave vector during the jet – intergalactic medium interaction. The results are presented in plots and can be used for determination of the plasma parameter values close to which the strong energy transfer and thermalization between the jet and the background plasma occur.

PROGRAM PACKAGE FOR 3D PIC MODEL OF PLASMA FIBER

A fully three dimensional Particle in Cell model of the plasma fiber had been developed. The code is written in FORTRAN 95, implementation CVF (Compaq Visual Fortran) under Microsoft Visual Studio user interface. Five particle solvers and two field solvers are included in the model. The solvers have relativistic and non-relativistic variants. The model can deal both with periodical and non-periodical boundary conditions. The mechanism of the surface turbulences generation in the plasma fiber was successfully simulated with the PIC program package.

Bremsstrahlung and Synchrotron Radiation from Planet Magnetospheres

Bremsstrahlung and synchrotron radiation from the moving charged particles was calculated in planet magnetospheres. A program package RADIATION was developed for these calculations. The radiative intensity is projected on a far sphere. The directional dependence of the radiation during the penetration of charged particles through the polar cusp was calculated. The program package RADIATION can be also used for treating the radiation of plasma cluster penetrating through the electric double layer, MHD and compress magnetic bow shock, plasma fibers and pinches and in other important situations. Intensity of radiation was derived from advanced and retarded potentials calculated from the Maxwell set of equations. Only radiative fields are displayed (I ∼ 1/r2) and the space intensity distribution does not depend on the distance of the projection sphere. In future non‐radiative fields will be treated as well. In this case the distance of the projection sphere will be important parameter. The program was written...