High-power test of annular-ring coupled structures for the J-PARC linac energy upgrade

Tamura, Jun  ; Ao, Hiroyuki; Nemoto, Yasuo; Asano, Hiroyuki*; Suzuki, Takahiro*

ACSs are going to increase the beam energy of the J-PARC linac from 181 to 400 MeV. The 2011 Tohoku earthquake damaged the J-PARC facilities and the cavity conditioning was interrupted for two years. After the restoration of the facility, the two ACS cavities (M01 and M11) were conditioned. They achieved to 15-20% above the designed accelerating field of 4.2 MV/m. Since M01 was conditioned six years ago, the conditioning time required for M01 was drastically reduced from that for the first time. During the high-power operation for M11, which is an unique cavity equipped with a capacitive iris in a waveguide, no significant increase of the temperature and the discharge rate around the capacitive iris was observed. The vacuum pressure was sufficiently low (410 Pa) even from the view point of beam loss due to residual gas scattering. The more stable operation can be expected through one-month conditioning before beam commissioning.