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

Abstract

A protection system for five high-power wiggler/undulator beam lines has been 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 downstream of a beam line, the closing titanium-alloy blade of the Fast-Closing Valve (FCV) is exposed to an intense synchrotron radiation beam from a wiggler/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 computers, and a dedicated high-speed optical communication link that is connected to four high-power RF klystrons (500 MHz, 180 kWmax, each) at the storage 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-speed optical-fiber links. Upon detecting a vacuum failure at any beam lines, the system can dump the positron beam within 95 μs by tuning off the RF power before initiating closure of the FCV blade. The system allows the FCV blade to close within 12.4 ms before the insuring gas deteriorates the UHV of the storage ring. The result of an actual accidental vacuum failure at a wiggler beam line proved that the protection system could successfully protect the UHV of the storage ring.