Impurities reduction conditionings to recover best beam quality of J-PARC cesiated RF-driven H ion source with new parts exposed to plasma

Ueno, Akira  ; Okoshi, Kiyonori ; Ikegami, Kiyoshi*; Oguri, Hidetomo  

The J-PARC cesiated RF-driven H ion source is stably suppling about 58 mA beam with a duty factor of 1.25 % (0.5 ms25 Hz) for the J-PARC LINAC 50 mA operations. For them, only three plasma chambers (PCHs) of #7, #8 and #9PCHs among ten PCHs have been used since the transverse emittances are more superior than others for unknown reasons. However, the emittances were enlarged by 16 % with the #7PCH, in which the plasma electrode (PE) temperature control plate (PETCP) was replaced to brand-new one to solve the air leak at the VCR vacuum fitting. The impurities from the new parts exposed to the plasma seemed to cause the degradation. The beam with almost the best emittances was reproduced by #4PCH with a new PETCP, in which sapphire tubes were used instead of the 99.7 % alumina ceramics tubes, after a new 2-MHz RF power scanning impurities reduction conditioning for 48 hours.