KEKB加速器での冷陰極真空計に対する光電子の影響 Effects of Photoelectrons on Cold Cathode Gauges in KEKB Accelerator
Some cold cathode gauges (CCGs) in KEKB Accelerator show different behavior from other ones. These gauges have following characteristics : (1) The locations of these CCGs are limitted to just downstream side of bending magnets where the synchrotorn radiation is intense. (2) The discharge current is proportional to the beam current. (3) The discharge current is observed even without a permanent magnet of CCG. (4) The discharge current per unit beam current approaches to a constant value as the integrated beam current increases. From these characteristics, the observed abnormal discharge current of these CCGs is considered to be due to the photoelectrons generated by the synchrotron radiation. A simulation shows that the electrons are not generated inside of the beam chamber but inside the gauge chamber by reflected SR or accelerated photoelectrons that are produced inside the beam chamber. Attaching small dipole magnet at the neck of CCG port can remove the effect of secondary electrons.
真空 43(3), 235-238, 2000-03-20
The Vacuum Society of Japan