Practical experience in extending the ion source and injection system H--ion source duty cycle

The ion source and injection system H- Penning surface-plasma source is currently being developed on the ion source development rig at Rutherford Appleton Laboratory in order to meet the requirements for the next generation of high-power proton drivers. Finite element modeling has been used previously to study the effect of increasing the duty cycle. The main requirement to allow increased duty cycles is improved cooling. By simply reducing the thickness of a sheet of mica to improve thermal conductance to the cooling system, duty cycles of 1.5 ms at 50 Hz can be achieved. Slight increase in hydrogen flow rate is required as the duty cycle is increased. As the duty cycle is increased the output current reduces, however, there is no change in beam emittance. The source cooling system is described and the heat flows within the source are discussed