Lithium and Sodium Surface Ionization Ion Source Operation and Efficiency

Abstract

An ion source configuration has been developed which uses direct surface ionization from oxygenated tungsten to generate lithium or sodium ions with measured efficiencies ≥70%. Currents of several hundred microamperes of Li⁺ and Na⁺ have been extracted at current densities up to several milliamperes per centimeter squared. The interrelationship between the current obtained and source parameters such as ionizer temperature, alkali metal feedrate, and ionization efficiency are examined. The ionization efficiencies were directly measured using a surface ionization detector in conjunction with an ion beam on/off technique which is independent of the efficiency of the detector. The expressions used in the efficiency determinations are derived and the simplifying assumptions are discussed.