Fire in the accelerator structure assembly room at electron-positron injector linac


At 9:44 pm on April 3rd, on the KEK Tsukuba campus, a fire alarm went off in the accelerator structure assembly room at electron-positron injector linac (a general radiation area) and the fire department was called to the site.

The cause of the alarm was determined to be an electric pulse modulator used in microwave power source, which had suffered a burnout. This event did not cause any human injuries or radiation leakage. We apologize to everyone for any concern or alarm.


Time Action
9:44 pm Fire alarm goes off, 2 researchers from Accelerator division 5 go to the accelerator structure assembly room with the alert and confirm the presence of smoke.
9:52 pm As a safety precaution, the accelerator’s beams are aborted.
11:15 pm (approx.) Firefighters and KEK Tsukuba Campus Radiation Safety personnel enter the site, confirm that there is no danger from radiation, heat, etc. As there was no danger of fire spreading to radioactive isotopes, external shutters were opened and the room was vented naturally.
1:30 am, April 4th The fire is confirmed to be extinguished.

2. Pre-fire Conditions

A check around 7 pm noticed nothing out of the ordinary. Around 9:30 pm the pulse modulator was remotely confirmed to have stopped unexpectedly.

3. Fire Location and Cause

Performance tests of the accelerating structure require microwaves, and we believe that a pulse modulator used in their generation had an undetermined malfunction that caused it to emit smoke. The exact cause is under investigation.

4. Effect on Accelerator Experiments

The accelerator in the Electron-Positron Injector linac delivers electrons and positrons to the SuperKEKB collider and the Photon Factory light sources, but research carried out in the accelerating structure assembly room is entirely separate from these accelerators. This effect that this incident will have on on-going experiments is currently under investigation. Once it has been confirmed to be safe, the experiments plan to restart.