Interaction of ICRF Fields with the Plasma Boundary in AUG and JET and Guidelines for Antenna Optimization
- Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Garching (Germany)
- CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)
- ERM-KSN EURATOM Association-Belgian State, Brussels (Belgium)
- EURATOM/UKAEA, Culham Science Centre, OX14 3DB, Abingdon (United Kingdom)
- Institute of Plasma Physics ASCR, Euratom Association, Za Slovankou 3, Prague (Czech Republic)
- Department of Electronics, Politecnico di Torino, Torino (Italy)
W sputtering during ICRF on ASDEX Upgrade (AUG) and temperature rise on JET A2 antenna septa are considered in connection with plasma conditions at the antenna plasma facing components and E{sub parallel} near-fields. Large antenna-plasma clearance, high gas puff and low light impurity content are favorable to reduce W sputtering in AUG. The spatial distribution of spectroscopically measured effective W sputtering yields clearly points to the existence of strong E{sub parallel} fields at the antenna box ('feeder fields') which dominate over the fields in front of the antenna straps. The picture of E{sub parallel} fields, obtained by HFSS code, corroborates the dominant role of E{sub parallel} at the antenna box on the formation of sheath-driving RF voltages for AUG. Large antenna-plasma clearance and low gas puff are favorable to reduce septum temperature of JET A2 antennas. Assuming a linear relation between the septum temperature and the sheath driving RF voltage calculated by HFSS, the changes of the temperature with dipole phasing (00{pi}{pi}, 0{pi}{pi}0 or 0{pi}0{pi}) are well described by the related changes of the RF voltages. Similarly to the AUG antenna, the strongest E{sub parallel} are found at the limiters of the JET A2 antenna for all used dipole phasings and at the septum for the phasings different from 0{pi}0{pi}. A simple general rule can be used to minimize E{sub parallel} at the antenna: image currents can be allowed only at the surfaces which do not intersect magnetic field lines at large angles of incidence. Possible antenna modifications generally rely either on a reduction of the image currents, on their short-circuiting by introducing additional conducting surfaces or on imposing the E{sub parallel} = 0 boundary condition. On the example of AUG antenna, possible options to minimize the sheath driving voltages are presented.
- OSTI ID:
- 21335688
- Journal Information:
- AIP Conference Proceedings, Vol. 1187, Issue 1; Conference: 18. topical conference on radio frequency power in plasmas, Gent (Belgium), 24-26 Jun 2009; Other Information: DOI: 10.1063/1.3273710; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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