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An innovative magnetic configuration called ADCM (Asymmetric Deflection Compensation Magnets) has been recently proposed for the cancellation of the "criss-cross" deflection of ion trajectories in multi-beamlet negative ion accelerators. Such undesired deflection occurs due to the transverse magnetic field, which is necessary for the suppression of co-extracted electrons. In view of the application of this concept to the ITER Heating Neutral Beam Injector, the new configuration has been experimentally tested for the first time in 2016, in the framework of a research collaboration between Consorzio RFX and QST. [ABSTRACT FROM AUTHOR]

In order to compare the simulation and the experiments of the extracted H- beams in JT-60SA negative ion source, an analysis of H- ion transport has been conducted. It has been shown that, under the present conditions, the calculated beam profile correlates well with the experiments, and the majority of the extracted H- ions are produced at the surface of the extraction aperture. However, since those H- ions could contribute to beam halo, a careful evaluation of the beam optics, taking into account more realistic plasma potential will be needed in the future works. [ABSTRACT FROM AUTHOR]

The negative ion beam optics is studied quantitatively from the viewpoints of the heat loads due to the beam halo in the accelerator and the emittance of the negative ion beam by using the 3D3V PIC model combined with a Monte Carlo calculation, in which negative ion beam from plasma meniscus formation to the beam acceleration is modeled. As for the heat loads of the A2G and the GRG, the simulation result almost agrees with the experimental result. The simulation result indicates that the secondary electrons from the extractor also contribute to the heat load of the A1G. Moreover, the normalized rms emittance of the negative ion beam after the exit of the GRG are estimated to be around 0.25π mm mrad, which are compatible with the typical values of the negative ion sources. [ABSTRACT FROM AUTHOR]

R&D of high power density negative ion beam acceleration has been carried out at MeV test facility in JAEA to realize ITER neutral beam accelerator. The main target is H- ion beam acceleration up to 1 MeV with 200 A/m² for 60 s whose pulse length is the present facility limit. For long pulse acceleration at high power density, new extraction grid (EXG) has been developed with high cooling capability, which electron suppression magnet is placed under cooling channel similar to ITER. In addition, aperture size of electron suppression grid (ESG) is enlarged from 14 mm to 16 mm to reduce direct interception on the ESG and emission of secondary electron which leads to high heat load on the upstream acceleration grid. By enlarging ESG aperture, beam current increased 10% at high current beam and total acceleration grid heat load reduced from 13% to 10% of input power at long pulse beam. In addition, heat load by back stream positive ion into the EXG is measured for the first time and is estimated as 0.3% of beam power, while heat load by back stream ion into the source chamber is estimated as 3.5 ~ 4.0% of beam power. Beam acceleration up to 60 s which is the facility limit, has achieved at 683 keV, 100 A/m² of negative ion beam, whose energy density increases two orders of magnitude since 2011. [ABSTRACT FROM AUTHOR]