Observation of plasma density fluctuations by a heavy ion beam probe diagnostic with multiple cell array detector on the tokamak ISTTOK

The heavy ion beam probe (HIBP) diagnostic permits the measurements of electron density and plasma potential as well as their fluctuations. The use of a multiple cell array detector (MCAD) spreads the HIBP capabilities to make simultaneous measurements across the plasma column. Two sets of current-to-voltage converters with respective bandwidths of 400 kHz and 4 MHz have been tested. This upgrade of the MCAD electronics has allowed the observation of quasicoherent fluctuations in bulk plasma at frequencies between 100 and 200 kHz. The localization and frequency of bulk plasma fluctuations correlate with the magnetohydranamic activity of the plasma.