Generation and Characterization of Sub-Picosecond Electron Bunches [Thesis]

SUNSHINE (Stanford University Short Intense Electron Source), a facility to generate high-intensity, sub-picosecond electron bunches hence coherent radiation in the far-infrared (FIR), is realized. The system is composed mainly of an rf gun with a thermionic cathode and an alpha magnet serving as the bunch compressor. The electron beam is then accelerated to 30 MeV by a linac. The coherent radiation generated by the electron bunches cover the wavelength ranging from 40μm to more than 1 millimeter. Simulations of the beam dynamics in the rf gun are discussed in Chapter 2. The shock wave instability for low energy beams due to space charge force is studied in Chapter 3. The principle of magnetic compression is presented in Chapter 4. The bunch length calculation, both the simplified first order matrix formation and actual computation including the divergence effects are also discussed in Chapter 4 Both synchrotron and transition radiation from the electron beam are proved to be coherent. Indirect and direct measurements for the bunch length in comparison with simulations are shown in Chapter 5. Various effects that affect the bunch length and the reasons for discrepancy are described. My main contributions to this project are the formulation of shock wave instability, the first order matrix formulation of bunch compression, computations by six dimensional phase space coordinate trackings and collaboration in radiation and bunch length measurements. Throughout this thesis, cgs units are used. When conversion to MKS is necessary, the factors are enclosed in brackets.