Creation, transport and measurement of bright relativistic electron beams

This thesis deals with three topics relevant to linac-driven free electron lasers: the creation, transport and measurement of bright relativistic electron beams.;Thermionic microwave electron guns produce bright electron beams that are well suited to drive free electron lasers, FELs. The rf fields in the gun cause some of the emitted electrons to reverse direction and strike the cathode. These back-bombarding electrons heat the cathode limiting both the pulse length and time averaged current. The cathode heating is reduced if a transverse magnetic field is applied across the gun cavity to deflect back-bombarding electrons. We improve the thermionic microwave electron gun by redesigning the deflection magnet to minimize the back-heating power. Computer simulations show that transverse magnetic fields with rapid axial falloffs reduce the back-heating power more than fields that are axially constant. Experiments verify these simulations. The deflection magnet presently installed on the Mark III gun has a slow axial falloff and reduces the back-heating power by 31%. Using the simulation results we design a new deflection magnet having a rapid axial falloff. This magnet has been installed on the NCCU gun and reduces the back-heating power by 63%.;Improper transport of the electron beam through the beam line degrades the quality of the electron beam and lowers the performance of the FEL. We propose to improve the beam line commissioning and control procedures on linac-driven FELs by experimentally measuring the transfer matrix of each beam line section. The transfer matrix of a given section is measured by dithering the electron beam, measuring the beam vector before and after the section and inverting the subsequent data matrix. We minimize the beam line errors by minimizing the deviation between the experimentally measured transfer matrix and the design transfer matrix of each beam line section. While not experimentally verified, computer simulations show that this technique can be very effective in bringing the experimental beam line close to its design specifications.;The performance of an FEL depends on various characteristics of the electron beam used to drive it. The gain of the laser especially depends on the transverse phase space distribution of the electrons. Previously it has not been possible to measure the details of the transverse phase space distribution of high-energy electron beams with the precision required to predict FEL performance. Standard techniques for measuring the transverse phase space of relativistic electron beams treat the phase space distributions as ellipses and only measure the sigma matrices that define the ellipses. These techniques give no information about the detailed structure of the phase space distributions. We have developed a new technique to measure transverse phase space that combines quadrupole-scanning techniques with tomographic image reconstruction to measure the actual phase space distributions while making no a priori assumptions about the distributions. Using this process, we are able to reconstruct phase space distributions that are not elliptical. Both computer simulations and experiments verify that phase space tomography makes the detailed measurement of the phase space distributions possible at high energies. Detailed reconstructions of the phase space distribution of a 44 MeV electron beam from the Mark III FEL are presented.