We are developing a new RF gun for SuperKEKB. High-charge, low-emittance electron and positron beams are required for SuperKEKB. The required injection electron beam has a charge of 5 nC and an emittance of 20 mm-mrad at an energy of 7.0 GeV. In this linac, a photo cathode S-band RF gun will be used as the electron beam source. An advanced RF gun is required for high-charge, low-emittance beam generation. Thus, we developed a Disk and Washer (DAW) type photo cathode RF gun. LaB₆ and Ir₅Ce were tested as photo cathode materials. Normally, LaB₆ or Ir₅Ce are used as a thermionic cathode, however we evaluated the performance of the materials as a photo cathode. The beam commissioning results showed that Ir₅Ce has high quantum efficiency and long life time. Nd:YAG laser was used for RF gun operation. The SESAM (Semiconductor Saturable Absorber Mirror) mode locked laser was used for oscillator (frequency: 52 MHz). The obtained laser pulse energy was 4 mJ with pulse length of 30 psec at wave length of 266 nm. Finally, we obtained the beam charge of 4.8 nC by using the DAW type RF gun and Ir₅Ce cathode.

A massive earthquake, named “The 2011 off the Pacific coast of Tohoku Earthquake”, hit us on March 11, 2011. The accelerator building quaked at an acceleration of 1000 gal on the top floor. The accelerator column withstood the earthquake with the help of quake-absorbers attached to its bottom, and no acceleration tubes were damaged. However, thirty eight column posts out of 240 had cracks, a vacuum leek happened at the terminal ion source, and the beam line of the superconducting booster lost its proper alignment. By recovering these damages as quickly as possible, we were able to open the tandem accelerator for experiment on September 15, 2011. We would express sincere thanks for kind support and encouragement received in this severe time.

BigRIPS fragment separator is the in-flight fragment separator with the large acceptance and the high momentum resolution that consists of 42 superconducting quadrupole magnets and 6 room-temperature dipole magnets. It is the core experimental equipment of RI beam factory (RIBF) at RIKEN and used to produce a wide variety of RI beams through the fragmentation of stable beams as well as the in-flight fission of the uranium beam. The BigRIPS fragment separator started in operation in 2007 and since then, 145 kinds of RI beams have been produced and used in physics experiments. 47 new isotopes were discovered by using the BigRIPS fragment separator.

A new feed-forward control system to precisely control the amplitude and phase of the pulsed RF power in an electron linear accelerator (linac) is developed to make the accelerating field constant. Fast variations and ripples in the amplitude and phase in the RF pulses are compensated by modulating the amplitude and phase in the low-level system with a variable attenuator and phase shifter. The system is innovated the overdrive technique, which is commonly used in analog circuits, to speed up the slow response of the phase shifter, while the control signals are digitally processed; thus, the method is a hybrid of analog and digital techniques. By using the new control system, we find that the peak-to-peak variations in the amplitude and phase are reduced from 11.6% to 0.4% and from 6.1 degrees to 0.3 degrees, respectively, in 7.6-μs-long RF pulses for the L-band electron linac at Osaka University.

The 4th Accelerator Reliability Workshop (ARW2013) was held in Melbourne, Australia on April 14–19. The purpose of this workshop is to discuss how to achieve high accelerator reliability. The brief summary of the workshop is reported.