An Application of SIMS to Fusion Energy Research: Determination of Ion Impact Desorption Cross Sections

Measurements of plasma effects on materials are required in the design and evaluation of fusion reactor components. One of the more prevalent effects is ion impact desorption (IID) of surface impurities, which may influence plasma temperatures and fuel recycling rates. This paper describes the application of secondary ion mass spectrometry (SIMS) to measure IID processes. SIMS is well suited for laboratory measurements of plasma effects since the ion beam used for analysis also simulates the energetic particle flux emanating from a plasma. This attribute can be utilized to obtain IID cross sections. A low-energy ion accelerator, which produces mass-analyzed, neutral-free beams of H1+, H2+, and H3+ is used as a primary ion source. The release of impurities from a wall sample due to IID is monitored by observing the appropriate secondary ion emission rate. Cross sections for various ion, impurity, substrate combinations are determined as functions of incident ion energy and impact angle. This information is then used to calculate impurity release rates expected during reactor operation.