Development of bipolar-pulse accelerator for intense pulsed ion beam acceleration

To improve the purity of an intense pulsed ion beams a new type of pulsed ion beam accelerator named ≪bipolar pulse accelerator≫ (BPA) was proposed. To confirm the principle of the accelerator a prototype of the experimental system was developed. The system utilizes B_y type magnetically insulated acceleration gap and operated with single polar negative 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 ≈25 A/cm², duration ≈1.5 μs was injected into the acceleration gap by the plasma gun. The ions are successfully accelerated from the grounded anode to the drift tube by applying negative pulse of voltage 240 kV, duration 100 ns to the drift tube. Pulsed ion beam of current density ≈170 A/cm², duration ≈50 ns was obtained at 41 mm downstream from the anode surface. To evaluate the irradiation effect of the ion beam to solid material, amorphous silicon thin film of thickness ≈500 nm was used as the target, which was deposited on the glass substrate. The film was found to be poly crystallized after 4- shots of the pulsed nitrogen ion beam irradiation.