Ion and electron cyclotron wall conditioning in stellarator and tokamak magnetic field configuration on WEGA

Journal Article · Wed Feb 12 00:00:00 EST 2014 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.4864519· OSTI ID:22263853

Wauters, T.; Louche, F. ^[1]; Laqua, H. P.; Otte, M.; Preynas, M.; Stange, T.; Altenburg, Y.; Aßmus, D.; Birus, D. ^[2]; Urlings, P. ^[3]

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1. Association Euratom-Belgian State, LPP-ERM/KMS, 1000 Brussels (Belgium)
2. Max Planck Institute for Plasma Physics, EURATOM Association, 17491 Greifswald (Germany)
3. Max Planck Institute for Plasma Physics, EURATOM Association, 17491 Greifswald, Germany and University of Technology, Department of Applied Physics, Eindhoven (Netherlands)

Discharge wall conditioning is an effective tool to improve plasma performance in tokamaks and stellarators. RF Discharge Conditioning (RFDC) techniques are envisaged for use during operational campaigns on superconducting devices like the ITER tokamak and W7-X stellarator, as alternative to DC Glow Discharge Conditioning which is inefficient in presence of magnetic fields. This contribution investigates RFDC in both the ion and electron cyclotron range of frequencies (ICRF and ECRF) on the WEGA device (Max-Planck-Institute for Plasma Physics, Greifswald, Germany) as preparation for W7-X operation. ECRF discharges produced by localised absorption of RF power at EC resonance layers suffer from poor radial discharge homogeneity in the tokamak vacuum magnetic field configuration, severely limiting the plasma wetted wall areas and consequently the conditioning efficiency. The non-localised production of ICRF discharges by collisional RF power absorption features much improved discharge homogeneity making Ion Cyclotron Wall Conditioning (ICWC) the favoured RFDC technique for superconducting tokamaks. RFDC with the stellarator vacuum magnetic field needs to aim at sufficient plasma densities at and outside the last closed flux surface (LCFS), maximising the convective plasma flux along the open field lines to the wall. Whereas for ICRF discharges this condition is easily fulfilled, on WEGA for He-ECRF discharges this could be achieved as well by off axis heating close to the LCFS. In stellarator magnetic field configuration it is found that He-ICWC for wall desaturation is at least one order of magnitude more efficient than He-ECWC. Novel ECWC methods are proposed that can decrease this efficiency gap with ICWC to a factor 2-3. The efficiency difference is less pronounced in case of H{sub 2}-ICWC and ECWC for isotopic exchange.

• OSTI ID: 22263853
• Journal Information: AIP Conference Proceedings, Vol. 1580, Issue 1; Conference: 20. topical conference on radiofrequency power in plasmas, Sorrento (Italy), 25-28 Jun 2013; Other Information: (c) 2014 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION
CYCLOTRONS
ECR HEATING
EFFICIENCY
ELECTRON CYCLOTRON-RESONANCE
ELECTRONS
GLOW DISCHARGES
ICR HEATING
ION CYCLOTRON-RESONANCE
ISOTOPIC EXCHANGE
ITER TOKAMAK
MAGNETIC FIELDS
MAGNETIC SURFACES
PLASMA DENSITY
SUPERCONDUCTING DEVICES
WEGA STELLARATOR