Bunch length measurements in CESR using an X-ray sensitive photoconducting detector

Single bunch longitudinal measurements at the Cornell Electron-Positron Storage Ring

“…Earlier measurements of the CESR bunch length, using an x-ray sensitive photoconducting detector and the beam spectrum, as a function of current have shown no bunch lengthening [1,2]. The resolutions of these previous measurements were not capable of measuring the effects presented in this paper.…”

Beam instrumentation

“…If we now populate the phase orbit with particles whose betatron phases ~ just match the curve we've just described, they can then travel around the orbit and always arrive at any given position with the phase appropriate to that point. To account for nonvanishing chromaticity, therefore, we have to introduce a phase slewing down the length of the bunch: this works out to be ~ = ~Qmo " AT = ~AT (22) which involves the chromatic frequency ~ we encountered previously in eq. (19).…”

“…With the advent of extremely fast photodetectors, the bunch length can now be measured accurately with a resolution approaching i0 ps (3 mm of length). [22] Time and space discrimination can be combined if the beam's image is observed on a photodetector through an adjustable slit. For example, coherent beam motion produces corresponding intensity fluctuations if the slit is offset from the center of the image.…”

“…(These can be bypassed by suitable pulse clipping with a shorted stub.) [22] The observation of such fast waveforms normally requires the use of a sampling oscilloscope, placed not too far from the detector itself.…”