Phaedrus-T probe techniques

Abstract

Probe techniques employed in ohmic, rf, and H-mode Phaedrus-T tokamak plasmas are discussed. The floating potentials of nonemitting probes are found to be insensitive to plasma potential fluctuations at the rf frequency. Both Langmuir and emissive probes have been swept. The Langmuir probes were swept into electron saturation where a low-frequency oscillation was sometimes observed. Large probes (biased electrodes) have been used to perturb the plasma into an H mode. The biased electrode I-V characteristics differ from those of nonperturbing Langmuir probes and can be used to help identify the H mode. Probe behavior during the H mode is discussed. Two novel reciprocating probe designs have been developed. The faster of the two achieves average speeds of 5 m/s, which to our knowledge makes it the world’s fastest.