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.

Dynamics and Electronegativity of Oxygen RF Plasmas

“…In comparison with the directly measured line integrated electron density of about 9.5 × 10 14 m −2 from MWI, the probe measurement provides a value which is by a factor of 2.7 lower. Such differences in the electron density determination, comparing interferometry and electric probe diagnostics, were also reported in the literature [30][31][32][33]. Moreover, the Druyvesteyn method assumes an isotropic electron energy distribution function and the transition of the electrons towards the probe as collision-free.…”

Triple Probe Measurements Benchmarked by Interferometry in a Pulsed‐Power Plasma

“…The magnetic flux density, which is up to 150 mT in this experiment, is not considered in the evaluation of data. Possible effects are discussed in paper [3]. In the present experiment the influence is probably small.…”

“…Possible reasons for the discrepancies are considered in reference [3]. During the contact of the probe with the plasma, rapidly rising currents and high absolute currents between the probe tips necessitate the consideration of inductances and resistances of the electrical circuitry.…”

On the relevance of magnetohydrodynamic pumping in solar coronal loop simulation experiments

“…In addition to these cameras the set of diagnostics comprises high-voltage probes and Rogowski coils, optical emission spectroscopy and a CO 2 laser interferometer 13 as well as electrostatic triple probes 14 and small magnetic pick-up coils protruding into the plasma. The gross behavior of the discharges is very FIG.…”