Modeling and Diagnostic of the Plasma of Magnetic Field Supported Discharges

Abstract

In this paper we present an experimental study of the variations of plasma parameters in both the axial as well as in radial directions in a 30 cm long cylindrical magnetron with outer cylindrically-shaped anode (diameter 58 mm) and coaxially placed cathode with a diameter of 1.8 cm. The measurements were made using three radially movable cylindrical Langmuir probes placed at three different axial positions between the magnetic coils. From the measurements there were evaluated electron density, electron mean energy, plasma potential and floating potential in dependence of the magnetic field (10 -40 mT) and the argon pressure (2 -7 Pa). In order to measure the axial variations of the discharge current, one half of the cathode length is segmented into 14 isolated segments with length of about 10 mm.The physical processes occurring in electrode regions and the positive column of a cylindrical magnetron discharge in crossed electric and magnetic fields are investigated basing on the solution of the Boltzmann kinetic equation by a multiterm decomposition of the electron phase space distribution function in terms of the spherical tensors. The influence of the distribution function anisotropy on the absolute values and radial profiles of the electron density and rates of various transport and collision processes is analyzed. The spiral lines for the directed particle and energy transport are obtained to illustrate the anisotropy effects in dependence on magnetic field. The electron equipressure surfaces are constructed in the form of ellipsoids of pressure and their transformation in the cathode and anode regions is studied. A strong anisotropy of the energy flux tensor in contrast to a weak anisotropy of the momentum flux density tensor is found. Particular results are obtained for the cylindrical magnetron discharge in argon at pressure 3 Pa, current 200 mA and magnetic fields ranging within 10 − 40 mT.

2‐D Experimental Study of the Plasma Parameter Variations of the Magnetically Sustained DC Discharge in Cylindrical Symmetry in Argon

“…It is consistent with the fact that larger surface of the anode (roughly three times that of the cathode) serves as an efficient collector of electrons even with "anode fall" with electronretarding field. The comparatively high mean energy of electrons in the positive column is the consequence of the fact that for electrons, which move in radial direction, the energy relaxation length with respect to elastic collisions exceeds the radius of magnetron, see [8].…”