Fast Lifetime Measurements of Stored e+/e- Single Bunches in PETRA and DORIS II Utilizing the AC-Signals of Simple Beam Current Transformers

A monitor for fast lifetime measurements has been developed and successfully tested. The monitor pick-up consists of a standard broadband transformer device in a ring position with equidistant bunch spacing. It has an upper cut-off frequency of about 4 MHz which allows to measure simultaneously the lifetimes of up to 8 individual bunches in PETRA (2 in DORIS II). In the electronic section the ac-signals are separated, baseline-restored, stretched and finally digitized in a highly stable 16 bit ad-converter. The output data are fed then into a microprocessor that computes the average currents and their time derivatives. As a result lifetimes of up to 5×104 s can be measured in less than 2 seconds. Some measurements are reported.