LiF ion source performance on PBFA II

Recent LiF ion source experiments have been conducted on Sandia National Laboratories´ Particle Beam Fusion Accelerator (PBFA) II [1]. This facility is designed to provide a 30 MV, 100 TW power pulse to an applied B ion diode to investigate the suitability of light ions for inertial confinement fusion (ICF). Singly-ionized lithium is the desired ion species for these experiments because it has the proper range in target materials at 30 MV. LiF-coated anodes have been shown in experiments on other accelerators [2,3] to produce relatively pure (>70%) Li⁺ beams. Earlier PBFA II experiments using porous anodes coated with LiF confirmed Li⁺ production from LiF films [4]. The present PBFA II experiments use 0.6 μm films of LiF evaporated onto a stainless steel anode surface to provide a 1 MA, 25 ns FWHM pulse of Li⁺ ions at energies of 6–9 MeV. The physical mechanism for production of ions from thin films of LiF has not previously been identified. One of us, T. Green, has developed a model which is consistent with LiF data from PBFA II and laboratory experiments and may provide a framework for understanding Li⁺ ion production from thin LiF films in an applied B diode.