Remarkable pressure rise at pumping port in J-PARC main ring

In J-PARC MR synchrotron with high power beam operation, the remarkable and endless pressure-rise over 10-4 Pa or more is found when a ion-pump of the ring turns off by accident or on purpose. This high pressure exceeds the normal pressure distribution of pump series and causes the beam loss by nuclear interaction. The outgassing rate depends on the existence of external magnet field at the pumping port, the initial pressure and the operating beam power. A minus potential synchronized with the operating cycle are found at the electrode in pumping port. The formation of electron cloud is considered to the pressure rise. (author)