Modeling a Helium Metastable Beam Source used in a Precision Helium Fine Stucture Experiment.*

A helium metatstable beam source used in precision laser spectroscopy of helium fine stucture is studied. The source, which uses electron excitation of a thermal helium beam, is described using a simplified analysis along with more detailed numerical modeling (with COMSOL Multiphysics®). These results are compared to experimental measurements and source performance. The expected effects of various parameters are examined, such as source pressure, background pressure, excitation/deexcitation cross sections, recoil, and electron space charge.