Generation and transport of a low energy intense ion beam

Abstract

The paper describes experiments on the generation and transport of a low energy (70–120 keV), high intensity (10–30 A/cm2) microsecond duration H+ ion beam (IB) in vacuum and plasma. The IB was generated in a magnetically insulated diode (MID) with an applied radial B field and an active hydrogen-puff ion source. The annular IB, with an initial density of ji∼10–20 A/cm2 at the anode surface, was ballistically focused to a current density in the focal plane of 50–80 A/cm2. The postcathode collimation and transport of the converging IB were provided by the combination of a “concave” toroidal magnetic lens followed by a straight transport solenoid section. With optimized MID parameters and magnetic fields in the lens/solenoid system, the overall efficiency of IB transport at the exit of the solenoid 1 m from the anode was ∼ 50% with an IB current density of 20 A/cm2. Two-dimensional computer simulations of post-MID IB transport supported the optimization of system parameters.