Arrangement of emissive and cold probes for fluctuation and Reynolds stress measurements

Abstract

An arrangement of three emissive probes and one cold probe was used to simultaneously determine the Reynolds stress and the fluctuation-induced flux in the edge region of the tokamak ISTTOK. The emissive probes are arranged in a 90º triangle and inserted into the tokamak so that two of the probes are separated radially and two are separated in the poloidal direction, with one probe being used for both directions. Since emissive probes deliver a better measure of the plasma potential than cold probes, with this arrangement the radial and the poloidal electric field and their fluctuations can be measured simultaneously, so that the Reynolds stress Re can be derived from the data. This setup is radially movable so that also the radial gradient of Re can be determined. In addition, a cold probe is inserted close to one of the outer emissive probes. The fluctuation-induced flux can be determined from a simultaneous measurement of the poloidal field fluctuations and those of the ion saturation current.