The Use of Emissive Probes in Laboratory and Tokamak Plasmas

Abstract

Abstract Emissive probes offer the possibility for a direct determination of the plasma potential since for sufficient electron emission its floating potential is ideally equal to Φ pl . By means of two such probes the true electric field can be derived. Emissive probes also deliver reliable results if there are electron drifts and beams in the plasma. A conventional emissive probe consists of an electrically heated loop of refractory wire. We have also developed emissive pin probes of graphite or LaB6, heated by a focused infrared laser beam. In this contribution we first discuss the question to what extent emissive probes perturb the plasma and thereby might falsify the measurement. Furthermore, we present recent measurements with an array of emissive probes in a small tokamak to detect plasma potential fluctuations and electric fields and the related radial plasma transport. Eventually, we present results of a laser‐heated emissive probe in a helicon discharge device (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)