Abstract
Multipactoring phenomena in a radio frequency (rf) input coupler, which could cause serious problems during accelerator operation, are described based on electrodynamics with the superposition state of the input and reflected waves in the coupler. Since the reflection coefficient varies widely with the beam loading in the case of high beam current storage rings, multipactoring zones should be represented in the two-dimensional space of the input rf power and the reflection coefficient. Based on this map, we have performed a simulation study for normal-conducting rf accelerating cavities and developed a method to operate an rf cavity with multipactoring problems so as to minimize the influence of multipactoring.
Highlights
The ARES [1,2,3], standing for accelerator resonantly coupled with energy storage, is a normal-conducting radio frequency accelerating cavity system for the KEK Bfactory (KEKB) [3,4,5,6,7,8,9,10,11,12]
We have developed a method to operate the above-mentioned rf cavity with the multipactoring problem, based on a multipactoring zone map, for the accelerator performance not to be degraded, by minimizing the influence of the multipactoring
The measurements were recorded when the high-energy ring (HER) accumulated a beam from zero current, so that the operating point started from the upper-left corner with ÿ 0:5 in the map, where the coupling-loop angle of the input coupler was set for the coupling coefficient of 3:0 before the KEKB operation
Summary
The ARES [1,2,3], standing for accelerator resonantly coupled with energy storage, is a normal-conducting radio frequency (rf) accelerating cavity system for the KEK Bfactory (KEKB) [3,4,5,6,7,8,9,10,11,12] This system makes it possible for KEKB to store high beam currents of electrons and positrons stably. The vacuum pressures rose up to several times higher values at certain input-power levels with and without a beam From this dependence of the vacuum pressures on the input rf power and discharge phenomena observed with a TV camera through the inside of the cavity, it turned out that the vacuum-pressure rises resulted from resonant electron multiplication in the coaxial line of the input couplers. The method of the multipactoring simulation and the zone map are explained, followed by an application of the map to an operational strategy against multipactoring
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