Coated Li Film Targets for TNSA Light-Ion Reaction Experiments with the MTW Laser*

A system for creating Sn or Ag coated Li targets was developed for a Multi-Terra Watt (MTW) laser Target Normal Sheath Acceleration (TNSA) experiment to study the ⁷Li(d,p)⁸Li reaction. The Li targets were designed to have a ∼50 nm thick coating to prevent Li from interacting with air and water vapor and be ∼2 µm thick to reduce energy loss. The films were produced in a ∼10^-5 Torr evacuated deposition chamber in which about 15 A flowing one way through a diode circuit heated a stainless-steel boat holding a Li pellet to a thermocouple-measured temperature of nearly 400°C, evaporating the Li onto a 25 µm thick stainless-steel substrate. A current of up to 60 amps flowing the opposite direction through another diode heated a molybdenum boat holding a Sn or Ag pellet, evaporating the metal and forming the thin coating over the Li. The thicknesses were measured using Rutherford backscattering, a magnetic adhesion tester, and a home-made profilometer. To allow Li metal to be weighed and inserted into the boat, an Ar-filled glove box was constructed around the deposition chamber.