The NIO1 negative ion source: Investigation and operation experience

The NIO1 (Negative Ion Optimization 1) source is developing a systematic test programme of magnetic configurations, including permanent magnet filter up to 15 mT dipole strength, tunable current filter up to 3 mT strength (parallel or perpendicular to the previous), and ion deflection compensation system in the extraction gaps. Results for both perpendicular and parallel configurations are presented. The radiofrequency (rf) system takes full advantage of the programmable frequency amplifier capability, to start the plasma and later to optimize coupling with plasma. Operation experience with borosilicate rf window and improved power limit are reported, as well breakdown voltages Vbr are discussed, together with improvements obtained with the installation of a cryogenic pump. The interrelation between bias voltage, bias plate current and magnetic configuration is outlined; cesium evaporators are in advanced development. Major diagnostic systems (including cameras and emission spectrometers) have been integrated with the acquisition system along with the data measured by several power supplies (including the high voltage supplies, the rf generator and bias supplies, the pressure measurements and the beam currents): among the several diagnostic used, the role of simple current measurement and some optical observation are noted.