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Title: Spectroscopic investigation of heavy impurity behaviour during ICRH with the JET ITER-like wall

Magnetically confined plasmas, such as those produced in the tokamak JET, contain measurable amounts of impurity ions produced during plasma-wall interactions (PWI) from the plasma-facing components and recessed wall areas. The impurities, including high- and mid-Z elements such as tungsten (W) from first wall tiles and nickel (Ni) from Inconel structure material, need to be controlled within tolerable limits, to ensure they do not significantly affect the performance of the plasma. This contribution focuses on documenting W and Ni impurity behavior during Ion Cyclotron Resonance Heating (ICRH) operation with the new ITER-Like Wall (ILW). Ni- and W-concentration were derived from VUV spectroscopy and the impact of applied power level, relative phasing of the antenna straps, plasma separatrix - antenna strap distance, IC resonance position, edge density and different plasma configuration, on the impurity release during ICRH are presented. For the same ICRH power the Ni and W concentration was lower with dipole phasing than in the case of −π/2 phasing. The Ni concentration was found to increase with ICRH power and for the same NBI power level, ICRH-heated plasmas were characterized by two times higher Ni impurity content. Both W and Ni concentrations increased strongly with decreasing edge density whichmore » is equivalent to higher edge electron temperatures and more energetic ions responsible for the sputtering. In either case higher levels were found in ICRH than in NBI heated discharges. When the central plasma temperature was similar, ICRH on-axis heating resulted in higher core Ni impurity concentration in comparison to off-axis ICRH in L-mode. It was also found that the main core radiation during ICRH came from W.« less
Authors:
 [1] ; ; ;  [2] ;  [3] ;  [4] ; ;  [5] ; ;  [6] ;  [7] ;
  1. Institute of Plasma Physics and Laser Microfusion, Association EURATOM-IPPLM, Hery 23 Str., 01-497 Warsaw (Poland)
  2. Max-Planck-Institut für Plasmaphysik, EURATOM-Association, D-85748 Garching (Germany)
  3. Department of Physics, Queen's University, Belfast, BT7 1NN, Northern Ireland (United Kingdom)
  4. CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France)
  5. Euratom/CCFE Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
  6. Association EURATOM - Belgian State, ERM-KMS, TEC Partner (Belgium)
  7. Euratom/CCFE Association, Culham Science Centre, Abingdon, OX14 3DB, UK and EFDA Close Support Unit, Garching (Germany)
Publication Date:
OSTI Identifier:
22263859
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1580; Journal 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)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANTENNAS; DENSITY; ELECTRON TEMPERATURE; ICR HEATING; IMPURITIES; ION TEMPERATURE; ITER TOKAMAK; L-MODE PLASMA CONFINEMENT; NICKEL; PLASMA; SPECTROSCOPY; TAIL IONS; TUNGSTEN; WALL EFFECTS