Characteristics of intense pulsed heavy ion beam by bipolar pulse accelerator

In order to improve the purity of the intense pulsed ion beam, a new type of a pulsed ion beam accelerator named “bipolar pulse accelerator” has been proposed. In order to confirm the principle of the accelerator, a double coaxial type bipolar pulse generator and a prototype of the experimental system were developed^{1, 2}. The bipolar pulse generator consists of a Marx generator and a pulse forming line (PFL) with a rail gap switch on its end. The system utilizes a magnetically insulated acceleration gap and was operated with the bipolar pulse. A coaxial gas puff plasma gun was used as an ion source, which was placed inside of the grounded anode. Source plasma (nitrogen) of current density of ≈ 30 A/cm² and pulse duration of ≈ 1.0 μs was injected into the acceleration gap. When the bipolar pulse with voltage of about ±110 kV and pulse duration of about 70 ns was applied to the drift tube, the ions were successfully accelerated from the grounded anode to the drift tube in the 1st gap by the negative pulse of the bipolar pulse. The pulsed ion beam with current density of 70 A/cm² and pulse duration of ≈ 50 ns was obtained at 50 mm downstream from the anode surface. The energy spectrum of the ion beam was evaluated by a magnetic energy spectrometer. The ion energy was in reasonable good agreement with the acceleration voltage, i.e., 1st pulse (negative pulse) voltage of the bipolar pulse.