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

Ueno, Akira  ; Okoshi, Kiyonori ; Ikegami, Kiyoshi*; Takagi, Akira*; Shinto, Katsuhiro   ; Oguri, Hidetomo  

In order to operate the J-PARC cesiated rf-driven H ion source with a beam intensity of 66 mA stably, the conditions to minimize the extraction electrode current (I), whose main component is the electron current co-extracted with the beam, were investigated. The 66 mA H ion beam with a low I of about 40 mA, which was one-fourth of that in the ordinal operation, were stably extracted by optimizing a rod-filter-field (RFF), a cesium (Cs) density and an axial magnetic field correction (AMFC). Especially, the AMFC of only 40 Gauss had the largest I reduction of about one-third. The corresponding 95 % beam transverse normalized rms emittances were degraded about 24 % due to the higher RFF and Cs density. The source will be operated in the conditions to compromise the stability and the beam quality by the investigated results.