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SFB 591 » Projekte » A9
 

Title

Collisionless heating in plasmas with strongly inhomogeneous magnetic fields

Project manager

Prof. Dr. Uwe Czarnetzki
Institut für Experimentalphysik V
Ruhr-Universität Bochum

Prof. Dr. Ralf Peter Brinkmann
Institut für Theoretische Elektrotechnik
Ruhr-Universität Bochum

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  Summary
  Goals

The subject of the subproject is the investigation of the smooth heating of electrons by high frequency electrical alternating fields in strongly inhomogenous magnetic fields. The intended esperimentelle configuration is a neutral-loop-discharge. It concerns a new decharge form, which was suggested recently by Uchida. The goal of the work exists in the development of a detailed physical understanding of the observed processes like the smooth heating in this configuration. The project plan covers each other supplementing experimental work, theoretical model studies and realistic numerical simulations.

The experimental research is to clarify by different, co-ordinated diagnostics techniques the processes for the neutral loop dicharge. The central research aim is the phase- and space-determination of the plasma density and the energy distribution of the electron component. Within a small energy range (<12eV) the density is sufficient for the application of the Thomson-dispersion, the range above the latter should be investigated by the measurement of the emission intensity of selected lines of the decharging gas and/or suitable admixtures. The optical measurements should be supplemented by Langmuir-probe-measurements, which however must be regarded critically in magnetized plasmas. The distribution of the induced electrical field is to be determined by so called B-dot-probes. In the sum thereby a fairly complete picture is given about the experimentally accessible parameters.

The parallel theoretical work was divided into two parts. In the one, designation as "theoretical model studies", a simplified, (half-) analytic model of the electron heating on the basis of a two-zone model is to be outlined. To accomplish that, the volume of the plasma chamber is divided roughly into an internal, weakly magnetized and an outside, strongly magnetized zone. The internal zone is the actual heating zone, in which the electrondynamics is described by the methods of a non-local theory, i.e., by an ordinary differential equation for the localaveraged electron distribution function. The outer zone is drift-kinetically modelled and supplies effective boundary conditions. The "effect near numeric simulation" however will supply information about the local distribution function. For the development of an understanding of the heater mechanism, the close reciprocal effect and the comparison of experiment and theory is indispensable. The confrontation of the two theoretical concepts should permit conclusions on the role to the chaotic movement of the electrons and the associated "impact-similar" effect.

Subject of the planned investigation is the smooth heating of the electrons in inhomogenous magnetic fields by high frequency electrical fields, especially in the case of neutral loop discharge. This heating process is to be examined both experimentally as well as theoretically by the means of simulations. One aims at arriving at a deep understanding of the relevant process, esparticularly by a synergy between experiment and theory.

Experimentally, the spatial distribution of the electron density and the electron temperature (and/or the middle energy) as well as the structure of the energy distribution function (and/or the distribution of velocity function) are to be determined. In this context, both optical (Thomson-dispersion, emission spectroscopy) and electrical (Lamir probes, B-Dot-probes) diagnostic procedures are to be used. With these, measurements of all important parameters should be realized. Theoretically the heating process is to be treated in a kinetic context; the electron energy distribution and/or the electron distribution of velocity is to be determined without A-priori-postulations. Each other supplementing investigations are planned too: With the methods of the asymptotic scale analysis a place- and time-averaged effective model is to be worked out, which describes the dynamics of the electron energy distribution in form of a drift diffusion process on the energy scale. Parallel to it relativistic and localdissolved computer simulations without simplifying postulats are performed.

 
 
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