Impact of a narrow limiter SOL heat flux channel on the ITER first wall panel shaping

Nuclear Fushion

article

M. Kocan¹  R.A. Pitts¹  G. Arnoux²  I. Balboa²  P.C. de Vries¹  R. Dejarnac³  I. Furno⁴  R.J. Goldston⁵  Y. Gribov¹  J. Horacek³  M. Komm³  B. Labit⁴  B. LaBombard⁶  C.J. Lasnier⁷  R. Mitteau¹  F. Nespoli⁴  D. Pace⁸  R. Panek³  P.C. Stangeby⁹  J.L. Terry⁶  C. Tsui⁹  P. Vondracek³ 

[1] ITER Organization;JET-EFDA, Culham Science Centre;Institute of Plasma Physics;Ecole Polytechnique Fédérale de Lausanne, Centre de Recherches en Physique des Plasmas;Princeton Plasma Physics Laboratory, Princeton;MIT PSFC;Lawrence Livermore National Laboratory;General Atomics;University of Toronto Institute for Aerospace Studies

关键词: ITER;    limiter plasma;    heat flux density;    scrape-off layer;    first wall panels;    narrow feature;   

DOI  :  10.1088/0029-5515/55/3/033019

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

The inboard limiters for ITER were initially designed on the assumption that the parallel heat flux density in the scrape-off layer (SOL) could be approximated by a single exponential with decay lengthλ _q. This assumption was found not to be adequate in 2012, when infra-red (IR) thermography measurements on the inner column during JET limiter discharges clearly revealed the presence of a narrow heat flux channel adjacent to the last closed flux surface. This near-SOL decay occurs withλ _q ∼ few mm, much shorter than the main SOLλ _q, and can raise the heat flux at the limiter apex a factor up to ∼4 above the value expected from a single, broader exponential. The original logarithmically shaped ITER inner wall first wall panels (FWPs) would be unsuited to handling the power loads produced by such a narrow feature. A multi-machine study involving the C-Mod, COMPASS, DIII-D and TCV tokamaks, employing inner wall IR measurements and/or inner wall reciprocating probes, was initiated to investigate the narrow limiter SOL heat flux channel. This paper describes the new results which have provided an experimental database for the narrow feature and presents an ITER inner wall FWP toroidal shape optimized for a double-exponential profile withλ _q = 4 (narrow feature) and 50 mm (main-SOL), the latter also derived from a separate multi-machine database constituted recently within the International Tokamak Physics Activity. It is shown that the new shape allows the power handling capability of the original shape design to be completely recovered for a wide variety of limiter start-up equilibria in the presence of a narrow feature, even taking assembly tolerances into account. It is, moreover, further shown that the new shape has the interesting property of both mitigating the impact of the narrow feature and resulting in only a very modest increase in heat load, compared to the current design, if the narrow feature is not eventually found on ITER.

【 授权许可】

Unknown