Study on the time changes of the proton beam passing current from the ion source to the RFQ at J-PARC LINAC

Currently, in the J-PARC linac, beam commissioning between the ion source and RFQ mainly involves adjusting the extraction voltage of the ion source and the two solenoid magnets in the Low Energy Beam Transport line (LEBT) installed between the ion source and the RFQ. These parameters are determined to maximize the measured beam current at the current monitor (SCT) downstream of the RFQ. Previously, the SCT used as a reference had measured the beam current by cutting out a part of the macro bunch. However, to further improve the beam quality, we adjusted LEBT parameters using the newly measured method, which is an integrated whole macro bunch signal. The optimum value obtained by the new method differed from the previous. Therefore, to investigate the cause, we saved all the beam current waveforms of the SCT for reference and compared the ion sources and LEBT parameters of each. As a result, the current of the beam that passed through the RFQ changed over time within the macro bunch for certain ion source and LEBT parameter settings. In this presentation, we will introduce the above study results and discuss the cause of the temporal changes in beam current.