Electrostatic probe measurements in a pulsed-power plasma and comparison with interferometry

Abstract

Electrostatic probe measurements have been performed in order to derive plasma parameters in a pulsed-power discharge. The experiment has been designed to produce plasma filled arc-shaped magnetic flux tubes. The plasma is sustained by high current densities along the tube axis, which drive the arc-shaped structure to expand via the magnetic hoop-force. The electrostatic probe is located at a fixed position in space and scans over the minor diameter (≈3 cm) of the discharge arc while it passes. The probe is designed as an asymmetric triple probe in order to get instantaneous information on electron temperatures and densities. Peak values of up to 10 eV and about 2 × 1021 m−3 respectively were found. Owing to the high reproducibility of the experiment it was possible to take double probe characteristics in subsequent shots for comparison. In addition, the measurements of the line integrated density were performed by means of a CO2 laser interferometer. The results of the electrostatic triple probe in the investigated plasma regime are compared with the results of the laser interferometer. While the shapes of the density distribution are in reasonable agreement, the peak values derived from the triple probe underestimate the electron density by up to a factor of 5.