Bunch-purity measurements of synchrotron X-ray beams with an avalanche photodiode detector

Abstract

The bunch purity of synchrotron X-ray beams has been measured with an avalanche photodiode (APD) detector. The APD detector has several advantages for measurements of the bunch structure in a storage ring: the detector has a good time resolution of 100 ps (FWHM) and very low noise level. Moreover, the peak profile by the present APD device has only a short tail, or a full width of 1.4 ns at 10−5 maximum, so that a small peak adjacent, 2 ns apart, to the main peak can be clearly resolved in the bunch structure. A successful measurement of the purity between the main and second bunches of the order of 10−9 is reported.