Announcement on the suspension of the J-PARC main ring user operation

J-PARC Center

On April 24, 2019, it was observed that the field strength dropped by 2 % in the one of bending magnets (B15D) in the beam transport line from RCS to MR [See Figure 1 and 2]. After the investigation, we found insufficient insulation between conductors in coils of the B15D. It leads us to the conclusion that continuation of the stable operation of MR accelerator is difficult and we decided that user operation of MR would be suspended immediately.
We already started to product a new coil. User operation of MR will be resumed in the beginning of November, after the replacement in September.
We regret any inconvenience for all users of the Hadron and the Neutrino experimental facilities. We ask for your understanding.
In addition, we can mention that there is no leakage of radioactive materials due to this problem and that there is no impact on facilities and the environment.

Kazuo Hasegawa, Fujio Naito
Accelerator Division, J-PARC
Minako Abe
Public Relations Section, J-PARC


Figure 1. Beam Transport line between the RCS and the MR. Red mark indicates the B15D bending magnet.


Figure 2. Structure of the B15D bending magnet. The B15D electro-magnet is a dipole magnet and bends the proton beam 15 degrees. It has N-Pole and S-Pole with a coil. Each coil consists of 5 layers of 24 turns (totally 120 turns).