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

Okabe, Kota  ; Shibata, Takanori*; Moriya, Katsuhiro  ; Okoshi, Kiyonori ; Miyao, Tomoaki*; Otani, Masashi*; Liu, Y.*; Morishita, Takatoshi  

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 the reference and compared the new and previous parameters of the ion source and LEBT devices. As a result, it was found that the beam current that passed through the RFQ changed over time within the macro bunch for certain ion source and LEBT parameter settings.