Bunch Length Measurement and the Beam Spectra Observation Through High Power RF Waveguide System
A wide-band pick-up, which is mounted on the wall of waveguide between the klystron and the RF cavity, has been developed for measuring beam spectra in KEKB. The spectrum between 5 GHz and 20GHz is taken to calculate the bunch length. And the synchrotron oscillation is observed as the side band of revolution peak. The bunch length and synchrotron frequency are measured under the different momentum compaction factors {alpha} and different total RF voltages Vc. Measured bunch length is compared with the measurement of streak camera.
A WIDE-BAND PICK-UP FOR MEASURING BEAM SPECTRUM IN KEKB
A wide-band pick-up, which is mounted on the wall of waveguide between the klystron and the rf cavity, has been developed for measuring beam spectrum in KEKB storage-ring. The MAFIA simulation code and Network-Analyzer test-bench have been applied to design the pick-up structure. After investigation of various kinds of structures, a strip-line type pick-up, which has a bandwidth of 5~30GHz, is chosen. Some important considerations are also included, such as to avoid the couple of large fundamental forward power for safety. Measurement results of beam spectrum and synchrotron oscillation are presented in this paper.
IMPEDANCE MEASUREMENTS IN THE KEKB
In the KEKB storage rings, we have measured the current dependence of the betatron tunes and the damping rate to evaluate the broad-band transverse impedance. The measured impedances were cross-checked and exceeded the design value by a factor of more than five. The tranverse mode-coupling instability was observed in LER when chromaticity was reduced. We found that the main impedance source for the instability was caused by the vertical collimators. The impedance of the collimators was investigated by changing their aperture.