Recent developments in the ISTTOK heavy ion beam diagnostic

The heavy ion beam diagnostic (HIBD) presents a powerful tool for investigations of hot plasmas in thermonuclear devices with magnetic confinement. When injected into the plasma, the primary probing beam of singly charged positive ions is ionized to a doubly charged state by impact with the plasma electrons and separated from the primaries due to the confining magnetic field of the plasma device. The resulting secondary ions are collected outside the plasma. The plasma parameters that can be measured by the HIBD are: the plasma electron density and temperature, and the electric and magnetic potentials. On the small tokamak ISTTOK (R = 0.46 m, a = 0.085 m, B = 0.5 T, I_p = 4...6 kA, e> = 5 centre dot 10¹⁸ m^-3, T_e = 120 eV), the HIBD is based on a 20 keV Xe⁺ (or Cs⁺) beam injector and a multiple cell array detector (MCAD) collecting a fan of secondary Xe²+ (or Cs²+) ions emerging from the plasma along the primary beam trajectory. This paper describes the recent developments and improvements in the ISTTOK HIBD secondary beam detection. The capabilities of new detection system are illustrated by recent results of ISTTOK plasma MHD activity and electrode biasing studies. The on going developments of the multichannel multi-slit 90 degree cylindrical energy analyzer for the plasma potential and its fluctuations measurements and a novel approach of the HIBD use in real-time vertical plasma position control are also considered