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, B-t congruent to 0.5 T, I-p = 6-9 kA), based on multip le cell array detectors, aimed at the study of the time variation of the pl asma density, electron temperature, poloidal magnetic field, and plasma pot ential radial profiles. In this article we describe an alternative method t o the traditional electrostatic energy analyzers for measurements of the pl asma potential based on the time-of-flight technique. The initial results o f the measurements of the changes on the average plasma potential during to kamak discharges with minor disruptions are also presented. These results h ave been obtained measuring the time-of-flight of the ions of a pulsed prim ary beam from the electrostatic plates of the ion gun to the primary detect or. (C) 2001 American Institute of Physics.