Production of intense light ion beams on a multiterawatt generator

Abstract

The operation of a pinch-reflex diode as an intense pulsed ion-beam source has been scaled up to the multiterawatt PITHON generator. Ion beams with currents of 1 MA at 1.8 MeV have been extracted in a 130 kJ, 100-ns pulse. The corresponding ion production efficiency is 60%. Power losses were observed in interfacing the coaxial diode to the biconic vacuum feed of the generator. By using smaller area diodes, the average current density at the anode source was increased to 20 kA/cm2. Proton and deuteron beams were studied in both planar and spherical diode geometries. The ion beam is focused predominantly by self-magnetic fields for planar diodes and predominantly by electrode shaping for spherical diodes. Current densities exceeding 150 kA/cm2 were achieved with spherical diodes. The spatial evolution of the anode and cathode plasmas was studied by laser holographic interferometry. As the peak of the power pulse is approached, plasmas were observed to expand from the electrodes in fairly uniform profiles with steep density gradients and to accelerate across the vacuum gap. After peak power, anode plasma fluctuations and a high-velocity (30 cm/μs) axial plume develop; the latter expands radially coincident with collapse of the power pulse.