RF Measurements for Microgravity Dusty Plasmas*

Many common plasma diagnostic instruments are incompatible with microgravity dusty plasma experiments. Some instruments, such as Langmuir probes, are strongly perturbing of dust and plasma. Other instruments are limited by the practical weight and space restrictions of microgravity experiments. Active Plasma Resonance Spectroscopy (APRS) techniques are potentially well-suited to these microgravity dusty plasma experiments, and we are developing APRS techniques for application in devices such as COMPACT, a next-generation experimental device currently in development.

APRS is a broad category of radio-frequency (RF) plasma measurement techniques that includes, among others, plasma impedance probes (PIPs) and resonance-shift probes. APRS techniques apply low-power RF signals to a plasma and measure the plasma response to measure n_e and T_e­­. This talk will focus on a technique wherein we apply an RF signal to an electrode at the edge of the plasma and measure the response on other electrodes in the chamber. We will describe the method, discuss its pros and cons vis-à-vis other diagnostic methods, and present preliminary results.