Plasma potential and fluctuations measurements by HIBD with 90° cylindrical energy analyzer on the ISTTOK tokamak

Abstract

The Heavy Ion Beam Diagnostic (HIBD) is known as unique tool for direct measurements of plasma potential in fusion devices such as tokamaks and stellarators. On small ISTTOK tokamak (R = 0.45 m, a = 0.085 m, B = 0.5 T, Ip = 4 kA, <ne> = 4 × 1018 m−3) the HIBD is operated with primary Xe+ ion beam with E = 22−24 keV of energy and a Multiple Cell Array Detector (MCAD) to measure the product of plasma neσ and its fluctuations simultaneously at a number of sample volumes along primary beam trajectory across the plasma. To upgrade the ISTTOK HIBD capabilities to measure the plasma potential and its fluctuations a multichannel 90° cylindrical electrostatic energy analyzer (CEA) operated in a beam deceleration mode has been proposed.This paper presents the first results of the plasma potential and its fluctuations measurements by the one-channel CEA prototype operated in two-times deceleration mode and in real conditions of the HIBD experiments on ISTTOK. Using an indirect CEA calibration approaches, the value of the potential Φ ∼ −350 V has been measured in the plasma core. Also, the plasma potential fluctuations Φ∼ ∼ 40 V have been observed. The obtained results demonstrate and confirm the applicability of the 90° cylindrical electrostatic energy analyzer and its operation in deceleration mode for the plasma potential and its fluctuations measurements by HIBD.