Experimental experience and improvement of NIO1 H− ion source

The ion source NIO1 (Negative Ion Optimization 1) is a versatile multiaperture H− source capable of continuous regime operation, with the plasma generated by a 2 MHz/2.5 kW radiofrequency (rf) power supply and extraction of nine beamlets. It aims to partly reproduce the conditions of much larger ion sources, built or in construction for the neutral beam injectors of fusion devices, in a compact and modular ion source, where effects of individual source components can be rapidly verified and compared to simulation code results. Several modifications of the magnetic configuration (both inside the ion source and the embedded magnets inside the accelerator grids) were investigated. Saturation of beneficial effect of filter field at large strength (>0.01 T) leads us to use softer magnetic filters, and the advantages of a crossed deflection field are noted. The rf system takes full advantage of the generator bandwidth (0/ + 20 kHz used). The result database and the integration of major diagnostic systems with the control system are also summarized, with some details on voltage holding and beam uniformity.