2019 年 62 巻 8 号 p. 476-485
J-PARC 3 GeV rapid cycling synchrotron (RCS) is one of the highest beam power proton accelerators, which accelerates 8.3×1013 protons at 25 Hz up to 3 GeV, corresponding 1 MW beam power. Challenges for achieving an ultrahigh vacuum (UHV) region in the beam line come from the large static and dynamic outgassing. In the RCS vacuum system, turbomolecular pump was taken up as main pump because it can evacuate such continuous and additional outgassing with a large pumping speed in the wide pressure range. Turbomolecular pump also has the advantage of not causing pressure instabilities like ion pumps. The more than 10 years operation of the RCS vacuum system showed that the UHV was rapidly obtained from the atmospheric pressure or low vacuum. It was also shown that the large additional outgassing during the degassing of the kicker magnets or high-power beam operation was promptly evacuated by the turbomolecular pump due to its constant pumping speed in the wide pressure rage. Free-run touchdown, which is a typical trouble of the turbomolecular pumps, was resolved by the developments of both elongation of cables between pump and controller and improvement of the touchdown bearing. As the developments in anticipation of the future requirement for the extreme high vacuum region, the developments, which are the combination with NEG and a development of a turbomolecular pump with the rotor of titanium alloy, are undergoing.