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Title: RF sheath modeling of experimentally observed plasma surface interactions with the JET ITER-Like Antenna

Journal Article · · Nuclear Materials and Energy
 [1];  [2];  [3];  [4];  [1];  [5]; ORCiD logo [6]; ORCiD logo [7];  [3]
  1. Royal Military Academy (ERM/KMS), Brussels (Belgium). Lab. for Plasma Physics
  2. Max Planck Society, Garching (Germany). Max Planck Institute for Plasma Physics
  3. Alternative Energies and Atomic Energy Commission (CEA), Cadarache (France)
  4. Royal Military Academy (ERM/KMS), Brussels (Belgium). Lab. for Plasma Physics; Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE), EURATOM/UKAEA Fusion Association
  5. Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE), EURATOM/UKAEA Fusion Association
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  7. Polytechnic Univ. of Torino (Italy)
+ Show Author Affiliations

Waves in the Ion Cyclotron Range of Frequencies (ICRF) enhance local Plasma-Surface Interactions (PSI) near the wave launchers and magnetically-connected objects via Radio-Frequency (RF) sheath rectification. ITER will use 20MW of ICRF power over long pulses, questioning the long-term impact of RF-enhanced localized erosion on the lifetime of its Beryllium (Be) wall. Recent dedicated ICRF-heated L-mode discharges documented this process on JET for different types of ICRF antennas. Using visible spectroscopy in JET ICRF-heated L-mode discharges, poloidally-localized regions of enhanced (by ~2–4x) Be I and Be II light emission were observed on two outboard limiters magnetically connected to the bottom of the active ITER-Like Antenna (ILA). The observed RF-PSI induced by the ILA was qualitatively comparable to that induced by the JET standard, type-A2 antennas, for similar strap toroidal phasing and connection geometries. The Be II line emission was found more intense when powering the bottom half of the ILA rather than its top half. Conversely, more pronounced SOL density modifications were observed with only top array operation, on field lines connected to the top half of the ILA. So far the near-field modeling of the ILA with antenna code TOPICA (Torino Polytechnic Ion Cyclotron Antenna), using curved antenna model, was partially able to reproduce qualitatively the observed phenomena. A quantitative discrepancy persisted between the observed Be source amplification and the calculated, corresponding increases in E// field at the magnetically connected locations to the ILA when changing from only top to only bottom half antenna operation. This paper revisits these current drive phased and half-ILA powered cases using for the new simulations flat model of the ILA and more realistic antenna feeding to calculate the E// field maps with TOPICA code. Further, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating Slow Wave (SSWICH-SW) code, which couples slow wave evanescence with DC Scrape-Off Layer (SOL) biasing, is used to estimate the poloidal distribution of rectified RF-sheath Direct Current (DC) potential VDC in the private SOL between the ILA poloidal limiters. The approach so far was limited to correlating the observed, enhanced emission regions at the remote limiters to the antenna near-electric fields, as calculated by TOPICA. The present approach includes also a model for the rectification of these near-fields in the private SOL of the ILA. With the improved approach, when comparing only top and only bottom half antenna feeding, we obtained good qualitative correlation between all experimental measurements and the calculated local variations in the E// field and VDC potential.

Research Organization:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE; European Commission (EC)
Grant/Contract Number:
AC05-00OR22725; 633053
OSTI ID:
1761659
Journal Information:
Nuclear Materials and Energy, Vol. 19; ISSN 2352-1791
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

References (11)

Physics and engineering results obtained with the ion cyclotron range of frequencies ITER-like antenna on JET journal June 2012
RF current distribution and topology of RF sheath potentials in front of ICRF antennae journal July 2005
Impact of ICRF on the scrape-off layer and on plasma wall interactions: From present experiments to fusion reactor journal January 2019
Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the “wide sheath” asymptotic regime journal September 2012
Commissioning and first results of the reinstated JET ICRF ILA journal November 2017
ICRF-enhanced plasma potentials in the SOL of Alcator C-Mod journal December 2013
Estimates of RF-induced erosion at antenna-connected beryllium plasma-facing components in JET journal January 2016
TOPICA: an accurate and efficient numerical tool for analysis and design of ICRF antennas journal June 2006
Radio-frequency sheaths physics: Experimental characterization on Tore Supra and related self-consistent modeling journal June 2014
Main design features and challenges of the ITER-like ICRF antenna for JET journal November 2005
RF sheath-enhanced beryllium sources at JET’s ICRH antennas journal July 2013

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY