Evaluation of bake-out operation when new equipment is added to J-PARC MR

In the MR synchrotron of the J-PARC high-intensity proton accelerator, gas emission from the inner wall surface of the beam duct is constantly observed as the proton beam bunches passes through. The amount of gas released is larger with higher beam intensity and higher vacuum pressure, and conversely smaller in relation to the integrated charge or total beam current that has passed through. Since the area that was exposed to the atmosphere and worked on during maintenance has little time to exhaust from the atmosphere, the pressure is high when the beam operation is resumed, and since the beam passes through the area for the first time, a large amount of gas is released, causing the pressure to rise further, leading to beam instability and beam losses. To avoid this, a certain amount of time is necessary to promote gas release by intentionally reducing the intensity of the circumferential beam when operation is resumed, which we refer to as 'burnout operation'. Among various past installation operations, we extracted duct replacement at periodical arc sections and collimator replacement operations as comparable cases with complete conditions, and verified the effect of beam burnout from the exhaust curve of the vacuum pressure caused by the atmospheric exposure operation. The results show that the heat-baking process should be performed before the installation to reduce the burnout time, and that sufficient exhaust time should be ensured before the operation. (author)