Revised SRS Impedance Estimates

The broad band impedance of the SRS has been previously reported to be about 10 R as measured by current dependent bunch lengthening, but to be less than 6 R based on both radial beam size and mode shift data if realistic assumptions are made. Recently the bunch length has been measured with a fast photodiocle and this gives results about 25 8 shorter than with the stroboscopic image dissector previously used. The new bunch lengthening data indicates an impedance in the range 4-6 n that is in good agreement with the other methods.