Utility of a Baffled Probe for Measurements of Oscillations in Magnetized Plasma

Abstract

AbstractA baffled probe for distinguishing the oscillations of space potential and temperature in magnetized plasma is tested. The probe consists of a tungsten wire tip, oriented perpendicular to the magnetic field, that is partially shielded by ceramic baffles (masks). The probe works under the condition that the electron Larmor radius is much smaller than the probe radius, and the ion Larmor radius is comparable to or larger than the probe radius. The probe uses the same principles as Katsumata and plug probes, but has the advantage of convenient, realtime controllability of the ratio between electron and ion current while electrically floating, and insensitivity to uncertainties in the orientation of the probe tip relative to the direction of the magnetic field. By rotating the baffle configuration around the probe tip, the ratio between electron and ion probe current and consequently the relative sensitivity of the probe to oscillations of space potential and electron/ion temperature, can be adjusted. Thus, measurements of ac floating potential with different ratio of electron and ion currents allow us to distinguish oscillations of space potential from electron/ion temperature fluctuations. Experiments have been conducted in a fully ionized, barium plasma in the West Virginia University Q‐machine. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)