• Z. Fang, S. Anami, Y. Fukui, M. Kawamura, C. Kubota, S. Michizono, F. Naito, K. Nanmo, S. Yamaguchi
  KEK, Ibaraki
• H. Asano, K. Hasegawa, T. Itou, T. Kobayashi, S. Shinozaki, N. Tsubota
  JAEA/J-PARC, Tokai-mura
• E. Chishiro, H. Suzuki
  JAEA, Ibaraki-ken

The out­put en­er­gy of the J-PARC LINAC will be up­grad­ed from 181 to 400 MeV in the next two years by adding high-be­ta ac­cel­er­a­tion sec­tions. The up­grade of the FP­GA-based dig­i­tal LLRF con­troller for the 400 MeV LINAC will be pre­sent­ed in this paper. The new LLRF con­trol sys­tem works for both the 324 MHz low-be­ta and 972 MHz high-be­ta sec­tions. Many func­tions are added into the LLRF con­troller, such as 1) work­ing for dif­fer­ent RF fre­quen­cies, 2) grad­u­al­ly in­creas­ing the feed­back gains in the feed­back loop in­stead of fixed ones, 3) au­to­mat­ic chopped-beam com­pen­sa­tion, 4) au­to­mat­i­cal­ly switch­ing the beam load­ing com­pen­sa­tion in ac­cor­dance with the dif­fer­ent beam op­er­a­tion mode, 5) input rf-fre­quen­cy tun­ing car­ried out by a FPGA to match the rf cav­i­ties dur­ing the rf start-up, 6) au­to-tun­ing of the rf cav­i­ty tuner by de­tect­ing the phase curve of the rf cav­i­ty dur­ing the field decay in­stead of the phase dif­fer­ence be­tween the cav­i­ty input and out­put sig­nals.