Studies of high-brightness electron beams at the accelerator test facility.

摘要

The Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) is a user facility providing high brightness electron beams and synchronized high power lasers for researches in free-electron lasers and high-gradient laser acceleration schemes. The system consists of a radio-frequency (RF) electron gun with a photo-cathode, two SLAC linear accelerator (linac) sections and three experiment beamlines, as well as a 10-ps Nd:YAG laser and a high power CO{dollar}sb2{dollar} laser. The facility is capable of delivering electron bunches with temporal duration of 1-10ps, charge of the order of 1 nC, normalized emittance in the order of 10{dollar}sp{lcub}-6{rcub}{dollar} mm.mrad and energy up to 70 MeV. The research described in this dissertation represents a comprehensive study of the beam dynamics of the high brightness electron beams at the ATF accelerator system.; The charge emitted by the photo-cathode depends on the work function and the photon energy as well as the strength of the electric field. This relationship has been determined and it provides a convenient method to determine the laser to RF phase.; Standard techniques like the multiple-screen method and the quadrupole-scan method were used to characterize the transverse phase space. We have also developed computed tomography techniques for a detailed characterization of the transverse phase space. The longitudinal phase space is analyzed by a dipole energy spectrometer incorporated into transport line.; We developed a technique for selecting pico-second slices of the electron beam along the longitudinal position within the bunch.; Using the slice-selection technique, we measured the time duration of the electron bunches under different operating conditions of the electron gun. The bunch length is a function of the field gradient in the gun and the laser to RF phase.; The transverse phase space ellipses of different slices along the bunches were measured for a number of current settings of the emittance compensation solenoid. The changes in the relative orientations of the ellipses are consistent with the prediction by the relativities envelope equation. The dependence of the slice emittance on different system parameters was also studied.; Finally, the use of optical transition radiation for electron beam diagnostics was explored.