RF Compressor (SLED) Phase-Modulation to Reduce Peak Fields in the MAX IV Linear Accelerator

Abstract: Modern particle accelerators need strong electric fields in order to produce high energy particles. Such high voltages are typically reached by injecting pulsed radio frequency power through several steps of amplification. At the end, pulse compression is used to further improve the energy gain at the cost of pulse-length. A typical pulse compression method developed at the Stanford Linear Accelera- tor Center (SLAC) is the SLAC Energy Doubler (SLED), which modulates the outgoing wave-envelope using either the phase or amplitude of the incoming wave. Normal operation of the cavity dictates that the phase is shifted 180◦ at the final part of the pulse. This thesis, however, aimed to explore alternative operation modes in order to reduce the peak field of the output while retaining as much of the energy gain as possible. Previous work was examined and a suitable, linear phase-modulation was chosen to be implemented. In order to realize the modulation scheme, an appropriate phase-shifter and logic controller were chosen and tested in order to determine how the new system would affect phase-stability. Results seemed to indicate that the new system would have no major impact on this parameter. It was then deemed appropriate to install the system on one of the accelerating sections towards the end of the MAX IV linear accelerator. Results from the newly installed setup seemed to conform with the modelling work despite certain setbacks caused by the cavities inside the SLED being out of tune. Overall the implementation appears to have accomplished its task well.