Present status of J-PARC linac LLRF system

In the J-PARC linac, more than 15 years passed since the low level radio-frequency (LLRF) system were manufactured, and it is in a phase where failures increase due to aging deterioration. In the summer shutdown of 2020, we installed seventeen new digitizersinstead of some digitial boards of cPCI from DTL3 to SDTL16 for the digital feedback and feedfoward (DFB·FF) system. We had to rebuild the LLRF system for this installation of the new digitizer. But we were able to perform the user operatoin without serious trouble. Also, it was clear that the momentum od the output beam fluctuates depending on the humidity of the klystron gallery. The RF reference distribution system was improved to be able to measure the phase drift from the summer shutdown of 2020. For some measured phase drift values, the operation of phase drift correction has been started. (author)