Construction of a versatile negative ion source and related developments

The NIO1 project consisting of a 60 kV ion source (9 beamlets of 15 mA each of H 12) is jointly developed by Consorzio RFX and INFN-LNL, with the purpose of providing a test ion source, capable of working in continuous mode and in condition similar to larger ion sources for Neutral Beam Injectors. The modular design allows for quick replacement and upgrading of parts. While the main body of the ion source construction is progressing at industry, some parts were separately developed at participating institution, as described in the following. A water free Carbon Fiber Composite (CFC) calorimeter is considered, together with more traditional water cooled calorimeters. A small rf plasma generator was installed at INFN-LNL and several rf matching boxes and a Cesium heater controller prototype were tested. Plasma generator (at ground) is followed by a puller and a positively biased Faraday cup, so that beam current can be measured. Plasma density estimated with a 4 wire Langmuir probe is consistent with plasma rf simulation, even if electron distribution deviation from Maxwellian seems large; new electronics with extended DC voltage sweep and a second Langmuir probe circuit are being tested. Finally preparation of the NIO1 site has begun at RFX and installation of source is expected to start in the end of 2012

Installation of a versatile multiaperture negative ion sourcea)

Neutral Beam Injectors (NBI), which need to be strongly optimized in the perspective of DEMO reactor, request a thorough understanding of the negative ion source used and of the multi-beamlet optics. A relatively compact RF ion source, named NIO1 (Negative Ion Optimization 1), with 9 beam apertures for a total H− current of 130 mA, 60 kV acceleration voltage, is being installed at Padua, in Consorzio RFX, to provide a test bench for source optimizations in the framework of the accompanying activities in support to the ITER NBI test facility. NIO1 construction and status of the overall installation, including a high voltage deck and an optical cavity ring down spectrometer are here summarized and reported. Plasma and low voltage beam operations are discussed. Development of a sampling beam calorimeter (with small sampling holes, and a segmented cooling circuit) is also discussed

Experimental experience and improvement of NIO1 H 12 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

Beam and installation improvements of the NIO1 ion source

The NIO1 (Negative Ion Optimization phase 1) source can provide continuous beam operation, which is convenient for systematic parameter and equipment studies. Even in the pure volume production regime, the source yield was found to depend on conditioning procedures. Magnetic configuration tests continued adding magnets to the existing setup; the filter field component Bx has been progressively extended to span the -12 to 5 mT range, and as a trend, source performances improved with |Bx|. The progress of camera beam diagnostics and of the quality of the volume-produced H- beam is also shown. The status, off-line results, and reliability of a first NIO1 cesium oven are discussed; other upgrades in preparation (cavity ring down spectrometer, the end calorimeter, and conceptual tests of the energy recovery system) are also listed

Extraction of many H- beamlets from ion source NIO1

After installation of Mo liners in the source NIO1 (Negative Ion Optimization phase 1), hydrogen plasmas in a continuous regime operation (much longer than one hour) are routinely maintained, with more than 1 kW rf power and 0.5 Pa pressure, allowing a systematic investigation of pure H- volume effect, which requests a much lower acceleration voltage Vs 45 12 kV than future Cs operations at Vs 45 60 kV. A new extraction grid EG was installed (replacing some eroded insulators) and preliminary beam images are compared to old EG ones, discussing effects of different deflection field strength and need of intermediate values. Large improvements in beam diagnostics and the effect of installation of a cryogenic pump are also reported