Work function measurements during plasma exposition at conditions relevant in negative ion sources for the ITER neutral beam injection
- Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, 85748 Garching (Germany)
- Lst. f. Experimentelle Plasmaphysik, Universitaet Augsburg, 86135 Augsburg (Germany)
Cesium seeded sources for surface generated negative hydrogen ions are major components of neutral beam injection systems in future large-scale fusion experiments such as ITER. The stability and delivered current density depend highly on the work function during vacuum and plasma phases of the ion source. One of the most important quantities that affect the source performance is the work function. A modified photocurrent method was developed to measure the temporal behavior of the work function during and after cesium evaporation. The investigation of cesium exposed Mo and MoLa samples under ITER negative hydrogen ion based neutral beam injection relevant surface and plasma conditions showed the influence of impurities which result in a fast degradation when the plasma exposure or the cesium flux onto the sample is stopped. A minimum work function close to that of bulk cesium was obtained under the influence of the plasma exposition, while a significantly higher work function was observed under ITER-like vacuum conditions.
- OSTI ID:
- 22085906
- Journal Information:
- Review of Scientific Instruments, Vol. 82, Issue 2; Other Information: (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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