Digital master oscillator results for the ISIS synchrotron

Rutherford Appleton Laboratory in Oxfordshire is home to an 800 MeV synchrotron particle accelerator called ISIS. Its main function is to direct a beam of protons into a heavy metal target to produce neutrons for scientists to analyse condensed matter. A second harmonic system is being developed to upgrade the beam current from 200 muA to 300 muA in order to drive a second target station. This is being achieved by the inclusion of four second harmonic cavities to increase the width of the RF bucket. In the past the six fundamental cavities were driven by an analogue Master Oscillator but the extra cavities will bring more difficultly in the phasing of the system. This could be more easily and precisely controlled by using a Direct Digital Synthesis system (DDS) as the heart of a new digital Master Oscillator. This paper describes the results of the setting up and performance of the prototype instrument so far and the implications it has for the synchrotron.