Optimization of extracted beam orbit during acceleration at J-PARC main ring

During beam operation in J-PARC main ring (MR), if an equipment abnormality is detected, the beam will be discarded to the abort dump using fast extraction (FX) and beam operation will be stopped. This is done within 1 ms of operation time even during acceleration. Of the kicker magnets (KM) and septum magnets (SM) that construct the FX section, the charging patterns of the pulse-excited KM and low-field SM are difficult to synchronize with the increasing beam energy. Therefore, the beam extracted during acceleration will not follow the adjusted beam orbit extracted at 3 GeV flat bottom or 30 GeV flat top, and will not reach the abort dump center. It is necessary to avoid beam irradiation to places other than the beam dump. If a high-intensity beam is hit to the bellows or welded parts of the vacuum duct leading up to the beam dump, there is a possibility of damage. The change in beam orbit must be such that the arrival point to the abort dump within the 700 mm diameter of its cross section. By adjusting the charging pattern of the KM and low-field SM, and the current pattern of the high-field SM, we can get a solution that the beam would reach the abort dump even if it was extracted at any timing during acceleration. In the beam test in April 2023, beam extraction was performed at each timing of 5, 8, 15, 20, and 25 GeV during acceleration under the MR operating condition assuming beam supply to the neutrino experimental facility, and it was confirmed that all beams reached the abort dump. Each orbit was generally consistent with the simulation, and the expected result was obtained. (author)