Measurements of the Length of Intense Electron Bunches Using a Capacitive Probe and a 20-Ghz Sampling Oscilloscope

Measurements of the longitudinal profile of intense electron bunches with an energy of 100 keV, using a button monitor and a 20-GHz sampling oscilloscope, are presented in this paper. At this energy, which is intermediate between nonrelativistic and relativistic, the button response is quite different from the response in either of the two extreme cases. An analytical model of the response is presented. The resolution derived from this model is 80 ps at 100-keV beam energy. For more relativistic beams, a resolution of about 40 ps appears to be feasible. Great care has to be taken in avoiding resonances.