Baffled‐Probe Cluster for Simultaneous, Single‐Point Monitoring of Magnetized Plasma Fluctuations

Abstract

Key words Electric probe, probe array, magnetized plasma, potential and temperature oscillations. PACS 52.70.-m An array of baffled probes for the real-time monitoring of oscillating values of space potential, electric field and electron/ion temperature in magnetized plasma is assembled and tested. The multi-probe array samples a region with dimensions on the order or less than an ion gyroradius, essentially a single point, and does not require voltage sweeps. We refer to an array of probes contained within such a single point as a probe cluster. Here, we describe two versions of the baffled-probe cluster. In the first cluster, four independent coils of collection wire are mounted at 90-degree intervals around the circumference of a short, thin, cylindrical, four-bore ceramic tube. This tube slides into a larger-diameter, single bore, ceramic tube having four azimuthally separated masks (baffles), each lining up with a coil-coil gap on the 4-bore tube, and four baffle-to-baffle gaps, each lining up with a coil on the 4-bore tube. The second cluster uses a single four-bore ceramic tube, with four longitudinal slots to allow side access to each bore, and probes made from a single strand of collection wire. With the tubes oriented perpendicular to the magnetic field, the baffled-probe cluster is rotated around its axis in order to regulate the ratio between electron and ion currents to the baffled probes and, thereby, change the probes' relative sensitivity to space potential and temperature oscillations. This probe-cluster design has the advantages of realtime monitoring of magnetized-plasma fluctuations, post-acquisition determination of electron-temperature or ion-temperature time series, post-acquisition determination of cross-phase and coherence between fluctuations of individual plasma parameters, compact size, minimal plasma perturbation (probes are non-emissive), and relative insensitivity to alignment uncertainty. The clusters have been used for distinguishing temperature fluctuations from potential fluctuations in plasma of the WVU Q-machine.

Magnetically insulated baffled probe (MIBP) for low-temperature and fusion-boundary plasma studies

“…The similar proposition looks to be true for the baffled probe also [46,58]. In this case, the baffles can also somewhat reduce the ion current, which does not depend on the angle of its rotation and does not change ion current shape.…”

Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities

“…Note that both spectra ͑measured by open and closed probes͒ practically coincide with each other, except at the exciting frequency of 8 kHz and its harmonics ͑16, 24, and 32 kHz͒, which can be evidence of the insignificance of temperature oscillations at all frequencies except the harmonics of 8 kHz. 9,17 Note that it was shown in Ref. 9 that spectra Ṽ s − e T e and Ṽ s in Fig.…”

“…The oscillation measurements were conducted with the probe cluster ͑2͒, 17 which was at the distance of 175 cm from the mesh. The probe cluster had the following dimensions.…”

Plasma potential probes for hot plasmas

“…Besides the BPP, two other types of ESPs have been developed to measure the plasma potential directly: these are plug probes [119,120] and baffled probes [121][122][123][124]. Also these probes work only in strong magnetic fields, Fig.…”