Development of a high brightness, ohmically generated thin film lithium ion source

Abstract

Summary form only given. A pure lithium ion source with low source divergence capable of generating high current density beams (/spl ap/1000 A/cm/sup 2/) is required for pursuing the goal of light ion inertial confinement fusion using pulsed power. It is believed that a uniform fully ionized lithium plasma at the anode surface (/spl ap/100 cm/sup 2/) created just before arrival of the main power pulse (5-30 MV, 0.1-1 MA, 40-60 ns) will be superior to flashover or field-threshold lithium sources. One method being pursued at Sandia is the development of an ohmically driven thin film lithium source, often termed EMFAPS. The EMFAPS process consists of an electrical pulse driven through a thin film coated with or bearing lithium in alloy or compound. The high current flowing through the film increases its temperature and resistivity until the lithium is driven off as vapor. The resistive voltage drop across the film generates a plasma by a gas discharge. Low impedance, fast risetime pulsers provided by NRL (D.D. Hinshelwood) and Pulse Sciences Inc. are being assembled and evaluated as film current drivers for full scale anodes (/spl ap/70 cm/sup 2/). Smaller scale (/spl ap/1 cm/sup 2/) tests are underway to optimize film composition, current contact engineering, anode construction, impedance dynamics, and energy disposition. Plasma discharge cleaning, bakeouts, film design and material selection issues are also being characterized to improve ion purity.