Ultra-high vacuum protection system for synchrotron radiation beam lines with very high-power wigglers and undulators

A protection system for five high-power wiggler/undulator beam lines has be en built to protect the Ultra-High-Vacuum (UHV) (<10(-8) Pa) of the 2.5 GeV storage ring at the Photon Factory. At an instantaneous vacuum failure dow nstream of a beam line, the closing titanium-alloy blade of the Fast-Closin g Valve (FCV) is exposed to an intense synchrotron radiation beam from a wi ggler/undulator, causing a meltdown of the blade within 80 ms. This results in fatal damage to components of the storage ring and a long shutdown time . The protection system comprises UHV detectors, FCVs, beam line control co mputers, and a dedicated high-speed optical communication link that is conn ected to four high-power RF klystrons (500 MHz, 180 kWmax, each) at the sto rage ring. Constant communication is maintained between the high-power beam lines and the RF klystrons at a transmission rate of 70.4 MHz using high-s peed optical-fiber links. Upon detecting a vacuum failure at any beam lines , the system can dump the positron beam within 95 mu s by tuning off the RF power before initiating closure of the FCV blade. The system allows the FC V blade to close within 12.4 ms before the insuring gas deteriorates the UH V of the storage ring. The result of an actual accidental vacuum failure at a wiggler beam line proved that the protection system could successfully p rotect the UHV of the storage ring. (C) 1999 Elsevier Science B.V. All righ ts reserved.