Evaluation of FIREX ion beam driver performances

An evaluation of the performance of the 1.2 MV, 0.8 MA, 150 ns pulser for the Cornell Field-Reversed Ion Ring (FIREX) experiment has been carried out. This pulser drives an extraction geometry magnetically-insulated ion diode to produce an annular beam which is induced to rotate by cusp injection into a solenoid, forming an ion ring for magnetic fusion studies. The maximum possible amount of proton beam charge must be extracted, with voltage pulse shape within strict limits. Thus the performance of the pulser with its diode load is critical to the success of FIREX. In this paper, experimental data are compared to PSPICE simulations used in the pulser design, and the simulation model is adjusted to understand the actual performance parameters. Some initial problems with water switch construction have been corrected, and the pulser performance agrees rather well with the original design model, with small adjustments of several circuit element values. The actual diode load impedance history is not yet as favorable as the original simulation model, but with an evaporating foil (EMFAPS) active ion source this difference should decrease and optimum performance be obtained.