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Title: Limiter Observations during W7-X First Plasmas

During the first operational phase (referred to as OP1.1) of the new Wendelstein 7-X (W7-X) stellarator, five poloidal graphite limiters were mounted on the inboard side of the vacuum vessel, one in each of the five toroidal modules which form the W7-X vacuum vessel. Each limiter consisted of nine specially shaped graphite tiles, designed to conform to the last closed field line geometry in the bean-shaped section of the standard OP1.1 magnetic field configuration (Sunn Pedersen et al 2015 Nucl. Fusion 55 126001). Here, we observed the limiters with multiple infrared and visible camera systems, as well as filtered photomultipliers. Power loads are calculated from infrared (IR) temperature measurements using THEODOR, and heating patterns (dual stripes) compare well with field line mapping and EMC3-EIRENE predictions. While the poloidal symmetry of the heat loads was excellent, the toroidal heating pattern showed up to a factor of 2× variation, with peak heat loads on Limiter 1. The total power intercepted by the limiters was up to ~60% of the input ECRH heating power. Calorimetry using bulk tile heating (measured via post-shot IR thermography) on Limiter 3 showed a difference between short high power discharges, and longer lower power ones, with regards tomore » the fraction of energy deposited on the limiters. Finally, fast heating transients, with frequency >1 kHz were detected, and their visibility was enhanced by the presence of surface coatings which developed on the limiters by the end of the campaign.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [3] ;  [2] ;  [5] ;  [2] ;  [6] ;  [6] ;  [2] ;  [2] ;  [2] ;  [3] ;  [7] ;  [7]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Max Planck Inst. for Plasma Physics, Greifswald (Germany)
  3. Univ. of Wisconsin, Madison, WI (United States)
  4. Max Planck Inst. for Plasma Physics, Greifswald (Germany); Univ. of Szczecin (Poland), Inst. of Physics
  5. Forschungszentrum Julich (Germany)
  6. Univ. of Cagliari (Italy)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Report Number(s):
LA-UR-16-29457; LA-UR-16-27281
Journal ID: ISSN 0029-5515; TRN: US1700555
Grant/Contract Number:
AC52-06NA25396; SC0014210; 633053
Type:
Published Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 5; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC). Fusion Energy Sciences (FES) (SC-24); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Magnetic Fusion Energy; Stellarator, infrared imaging, limiter, power balance; Wendelstein 7-X, stellarator, plasma, heat loads, IR imaging
OSTI Identifier:
1349536
Alternate Identifier(s):
OSTI ID: 1352427; OSTI ID: 1357121