Optical and langmuir probe diagnostics in a magnetized hollow cathode arc

Abstract

The paper presents measurements of the plasma parameters of a hollow cathode arc (HCA) using Langmuir probes (LPs) as well as optical emission spectroscopy (OES). The plasma of a HCA is characterized by a high energy beam-like component of electrons which causes a relatively high ionization degree. Data of LP measurements were evaluated to obtain the electron energy distribution function (EEDF), which could be approximated by the generalized Druyvesteyn distribution. The spectroscopic method used is based on the analysis of the molecular spectra of nitrogen and the atomic spectra of He and Ar. By considering several lines with different excitation thresholds the EEDF could be obtained in a trial and error procedure using a regularization routine. Because of the high electron density in HCA, stepwise processes initiated by metastable states of Ar and He atoms and N2 molecules are taken into account also. The data evaluated from spectroscopic measurements are compared with those from LP measurements. The EEDF measured by OES could be approximated by a Maxwellian distribution function. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.