Speaker
Description
In J-PARC MLF (Materials and Life Science Experimental Facility), we maintain and operate 6 T0 choppers on JAEA instruments. The T0 choppers had been more than 10 years since they were installed, and they had begun to deteriorate over time, and performance improvements were also necessary.
We developed 2nd generation T0 chopper which is high-speed and high-durability, and 2 of them have been already replaced at 4SEASONS (BL01) and SENJU (BL18). In 2025, We replaced high-durability T0 chopper at TAIKAN (BL15).
The 2nd one is different from a previous one in various points. The mount of the 2nd one was designed to be compatible with previous one, but an extra vibration sensor and a few sensors for the phase control system are added. For that reason, we had to put some extra cables which are about 30 meters in total, and a junction device box had to be put between T0 chopper and control panel. At each beamline, various devices and machines have been already installed besides choppers under the shielding blocks and particularly TAIKAN has 3 large vacuum chambers whose width occupies almost full width of the beamline and there is little space to put the cables. Therefore, we carefully considered the way to install the T0 chopper and the space to put the cables. Moreover, the junction device box had to be put under the shielding, where the box has a possibility to be irradiated by scattered neutrons. To prevent the box from breakdown, we covered it with B4C resin.
The previous one has only 25Hz speed, but new one can run at 25, 50, 75, and 100Hz. At this point, the biggest problem is resonance. So, we have to consider resonance frequency at each speed. Additionally, peripheral equipment also has its own resonance frequency respectively. The T0 choppers rotate a heavy hammer at high speeds and, vibration from the T0 chopper could cause large effects to the equipment. Therefore, we took measures to prevent the problems from vibration.
The poster will describe the replacement of a T0 chopper and adjustment to mitigate vibration so that the chopper can be operated normally.
