Voltage holding and dark currents in the Cadarache 1 MV ion beam facility

We report our experience in obtaining high voltages up to 1 MV required for the acceleration of D/sup -/ beams. We find that satisfactory voltage holding at this level can be obtained by adding gas up to a few 10/sup -4/ mb. Obtaining the required voltage at lower pressures is made cumbersome by the appearance of leakage (or dark) currents. Since the reduction of the dark current by conditioning is very time consuming the most practical remedy is the reduction of the cathode and anode surfaces of the system.