Tohoku University, School of Scinece, Sendai
Generation of high brilliance beam using an RF gun is very attractive for advanced use of electron linacs. Beam dynamics in the RF gun has been studied theoretically so far, and many simulation codes have been developed. The stage in which the beam is extracted and accelerated to relativistic momentum is crucial for understanding of space charge dominated beams. In this sense, actual measurement of the beam phase space is highly desired to examine the validity of the simulation codes. However, for the low energy electrons, such measurement is difficult because the phase space is easily distorted due to space charge effect during travel through drift space. Accordingly, we have considered employing the energy dependent angular distribution of Cherenkov radiation. Though the emission angle of Cherenkov radiation decreases rapidly with increasing beam energy, it is still 25 deg/MeV at an energy around 2 MeV when we use a radiator that has a refractive index of 1.035. Thus the energy distribution can be measured by observing the Cherenkov ring with sufficient angular resolution. Since this method needs only a thin radiator, the drift space length can be minimized.
