Chemical sputtering studies of lithiated ATJ graphite

Lithium evaporation treatments in the National Spherical Torus Experiment (NSTX) have shown dramatic improvements in plasma performance increasing the viability of lithium as a Plasma Facing Component (PFC) material. In order to understand the complex system of lithiated ATJ graphite, chemical sputtering measurements of plain and lithiated ATJ graphite are conducted in our upgraded IIAX (Ion Surface Interaction Experiment) facility with a differentially pumped Magnetic Sector Residual Gas Analyzer (MSRGA). Chemical sputtering of graphite is dependent on the ion energy and substrate temperature, hence the effects of treating ATJ graphite with lithium in hydrogen plasma is investigated in terms of different target temperatures and bias voltages. For this purpose, lithium was evaporated in situ onto ATJ graphite and chemically sputtered species in hydrogen plasma were measured using MSRGA. The dominant chemical sputtering product was CH4. Initial experiments show that lithium treatments have suppressed the chemical sputtering of ATJ graphite. 2013 Elsevier B.V. All rights reserved.