Electron beam sizes and lifetimes at MAX II and MAX III

Sammanfattning: The MAX II and MAX III synchrotron light sources at MAX-lab provide synchrotron radiation for experiments in a wide variety of research fields. The synchrotron radiation is emitted by ultra-relativistic electrons circulating in electron storage rings. In this thesis the transverse and longitudinal electron beam sizes and the electron beam lifetime limitations in electron storage rings are discussed and the methods used at MAX-lab to measure them are described. The thesis describes how measurements of the electron beam sizes and lifetimes were used to investigate and improve the performance of MAX III and to evaluate a change in the MAX II vacuum system. MAX II was the first synchrotron light source to install nonevaporable getter (NEG)-coated dipole vacuum chambers. They were installed in order to test the feasibility of the MAX IV 3 GeV storage ring vacuum design, where NEG-coated dipole chambers are an integral part of the design. From measurements of the lifetime limitations in MAX II it was concluded that NEG-coated dipole vacuum chambers do not appear to have any negative impact on the performance and operation of a synchrotron light source. A diagnostic beam line was designed and installed in MAX III in order to determine the transverse electron beam profile. The performance of the beam line was investigated by conducting a series of measurements at different beam line settings. There was good agreement between the determined beam sizes for the different settings. The diagnostic beam line was used to determine the horizontal and vertical dispersion and emittance in MAX III at low currents, and an increase in the momentum spread from longitudinal instabilities at higher currents. By adding a second passive Landau cavity to the MAX III radio frequency (RF) system the instabilities were damped in the main window of operation. Measurements of the longitudinal beam size and the induced voltages in the passive cavities agreed well with computer simulations of the triple RF system of MAX III. At high Landau cavity voltages a stable overstretched bunch shape with two regions of phase stability was observed. The lifetime limitations and acceptances in MAX III were determined and the location of a horizontal aperture restriction was identified. Removing the aperture restriction increased the lifetime in MAX III by a factor of two.