DEPOSITION SYSTEM FOR THIN LITHIUM NUCLEAR TARGETS

Abstract

A system was developed to create Sn or Ag coated Li nuclear targets for ICF simulation and Target Normal Sheath Acceleration (TNSA) experiments. The purpose of these experiments is to develop ways to measure low energy light-ion cross sections using high-power, ultra-fast lasers. The Li targets were designed to have a ~50 nm thick coating over a 2 μm thick Li film to prevent the Li from reacting with air and water vapor. The films were produced in a ~10−5 Torr evacuated deposition chamber. Approximate 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 A 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 film thicknesses were measured using Rutherford backscattering, a magnetic adhesion tester, and a home-made profilometer. To allow Li metal to be weighed and inserted onto the boat without oxidization, an Ar-filled glove box was constructed around the deposition chamber.