The H- multiaperture source NIO1: gas conditioning and first cesiations

In NIO1, a compact H- ion source installed at RFX operated in continuous mode, gas conditioning was needed to improve results in Cs-free regimes (up to a current density about 25 or 30 A/m2). Installation of a cesium oven gave an additional increase of current, progressively limited also by a rapid overcesiation: we observed an average density about 50 A/m2 (with a peak of 67 A/m2). Obtained beam optics is briefly compared with simulations and previous results in the Cs-free regime in similar conditions (as source voltage, often set below or equal 11 kV). In both regimes, central beamlet apparent density is larger, possibly because of a narrow bias plate mask, now enlarged. Further improvements for Cs-based regime include a moderate oven reservoir temperature, careful tuning and a substantial increase of beam voltage, and power handling capability.