Design of a laser-produced lithium anode plasma experiment on the Helia extraction diode

Abstract

Summary form only given, as follows. Recent experimental evidence on PBFA II (Particle Beam Fusion Accelerator II) has suggested that poor source turn-on and nonuniformity may contribute to the late focusability achieved with passive lithium ion sources to date, further emphasizing the need for a preformed anode plasma. The authors are planning to field a direct laser-produced lithium anode plasma source on the Helia extraction diode experiment, with eventual application to PBFA II. Previous experiments have shown that a high-density lithium plasma can be produced by direct laser irradiation of a solid lithium surface with a pulsed dye laser (LIBORS) tuned to the Li I 2s-2p resonance line (670.8 nm). These measurements have also suggested that the plasma formation process, and therefore the laser energy requirement, is dominated by the thermal energy required for vaporization with the long-pulse (1- mu s) LIBORS laser. They developed a simple model of this process and have investigated the effects of laser pulse length, lithium film thickness, substrate material, and laser wavelength on the threshold for lithium plasma production. Their results, which support the earlier results, are summarized.<>