ISIS Ion Source Operational Experience

The ISIS ion source is a surface plasma ion source of the Penning type, and routinely produces 35 mA of H − ions during a 200 µs pulse at 50 Hz for uninterrupted periods of up to 40 days. A new computer control system was installed in 1995, which, in addition to providing much tighter control of ion source parameters, has allowed these parameters to be logged every fifteen minutes and then averaged on a daily basis. A detailed analysis of these data from every ion source run on ISIS during the last five years shows the range of regimes under which operation is possible, but highlights the adverse effects that certain modes of operation may have. Evidence is provided that apparently small mechanical defects can have a marked impact on how an individual ion source behaves. Practical experience has determined the parameter changes necessary to maintain optimum performance. These typical changes are seen in the logged data and explained in terms of ion source physics. This design of ion source will be used on the RFQ test facility at Rutherford Appleton Laboratory (RAL), and an improved version may be viable for the European Spallation Source project.