How to make extraction electrode current lower than beam and corresponding beam qualities in J-PARC cesiated RF-Driven Hˉ ion source 66 mA operation

The beam brightness of the Japan Proton Accelerator Research Complex cesiated RF-driven H− ion source has been increased by using several unique measures, such as a low plasma electrode temperature operation, slight H2Os feeding in hydrogen plasma and so on. The source enables high energy linear accelerators (LINACs) to eject a beam with 60 mA peak intensity. In order to use the source stably for the LINACs operated with a duty factor higher than the present value of 1 msec×25 Hz, the conditions to minimize the extraction electrode current (IEE), whose main component was the electron current co-extracted with a 66 mA beam, were investigated. The 66 mA Hˉ ion beam with a low IEE of 39 mA, which was about one-fourth of that in the ordinary operation, were stably operated by optimizing rod-filter-field (RFF), cesium (Cs) density and axial magnetic field correction (AMFC). Especially, the AMFC of only -30 Gauss had the largest IEE reduction by about one-third. The corresponding 95 % beam transverse normalized rms emittances were degraded by about 24 % due to the Cs density and RFF higher than those in the ordinary operation.The beam brightness of the Japan Proton Accelerator Research Complex cesiated RF-driven H− ion source has been increased by using several unique measures, such as a low plasma electrode temperature operation, slight H2Os feeding in hydrogen plasma and so on. The source enables high energy linear accelerators (LINACs) to eject a beam with 60 mA peak intensity. In order to use the source stably for the LINACs operated with a duty factor higher than the present value of 1 msec×25 Hz, the conditions to minimize the extraction electrode current (IEE), whose main component was the electron current co-extracted with a 66 mA beam, were investigated. The 66 mA Hˉ ion beam with a low IEE of 39 mA, which was about one-fourth of that in the ordinary operation, were stably operated by optimizing rod-filter-field (RFF), cesium (Cs) density and axial magnetic field correction (AMFC). Especially, the AMFC of only -30 Gauss had the largest IEE reduction by about one-third. The corresponding 95 % beam transverse normalized...