Longitudinal Phase Space Measurements of Short Electron Bunches Using a 17 GHz Circularly Polarized Beam Deflector

Operation of a chopper‐prebuncher high voltage injection system and a high gradient 17 GHz linac having an inherent ability to generate 1 degree (162 fs) electron bunches emphasized the need for a simple means of accurately measuring very short electron bunches while also providing on‐line guidance for optimizing the injector and linac bunch length controls. To meet this need, a fast diagnostic for the direct measurement of short bunch longitudinal phase space, with a time resolution of less than 100 fs, has recently been installed on the 17 GHz linac at the MIT Plasma Science and Fusion Center. The diagnostic system, having a high field (0.2 MA/m) circularly polarized 17 GHz beam deflector, is described; images of 17 GHz electron bunches are shown; and bunch charge distributions mapped with a matrix of 150 micron diameter collimators spaced on 240 micron centers (sampling intervals of 40 fs and 0.4% Δp/p) are presented. The minimum time resolution of this fast diagnostic device is linearly dependent on t...