Impurities Reduction Conditionings to Recover Best Beam Quality of J-PARC Cesiated RF-Driven H- Ion Source with New Parts Exposed to Plasma

Abstract

Abstract For the J-PARC operations, only three plasma chambers (PCHs) of #7, #8 and #9PCHs among ten PCHs have been used since the transverse emittances of the beam produced with them are more superior than those with others for unknown reasons. However, the #7PCH beam emittances were enlarged by 16 % with a brand-new plasma electrode temperature control plate (PETCP) 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 after a new impurities reduction conditionings for 48 hours, in which the impurities produced by the plasma were reduced as small as possible by scanning both of 2-MHz-RF power and axial magnetic field in #4PCH.