Measurements of the plasma potential by HIBP using a TOF method

A heavy ion beam diagnostic is being developed for the tokamak ISTTOK (R=0.46 m, a=0.085 m, Bt≅0.5 T, Ip=6–9 kA), based on multiple cell array detectors, aimed at the study of the time variation of the plasma density, electron temperature, poloidal magnetic field, and plasma potential radial profiles. In this article we describe an alternative method to the traditional electrostatic energy analyzers for measurements of the plasma potential based on the time-of-flight technique. The initial results of the measurements of the changes on the average plasma potential during tokamak discharges with minor disruptions are also presented. These results have been obtained measuring the time-of-flight of the ions of a pulsed primary beam from the electrostatic plates of the ion gun to the primary detector.