Study of oscillating magnetized hollow cathode arcs by time-resolved Thomson scattering measurements

Abstract

A spatially resolving incoherent Thomson scattering technique has been used for time-averaged and time-resolved investigations of a magnetized hollow cathode arc burning in hydrogen and helium. In these plasmas strong self-excited oscillations with frequencies between typically 10 and 60 kHz are found generating modulated plasma emission intensities and discharge voltage signals. In the case of periodically oscillating plasmas, space- and time-resolved measurements of electron density and temperature are performed over the arc cross section by proper triggering of the pulsed laser system with the periodically oscillating voltage signal from the plasma. The evaluation of the electron density and temperature contour maps reveals that the region of maximum electron density is shifted eccentrically and rotating azimuthally around the arc axis. The region of maximum electron temperature shows a nearly annular shape, following the dimensions of the hollow cathode. When increasing the external magnetic field and neutral gas pressure, the arc motion and time behaviour of individual plasma parameters become irregular and chaotic.