Energetic ion transport by microturbulence is insignificant in tokamaks

微視的乱流による高エネルギーイオンの輸送はトカマクにおいて顕著でない

Pace, D. C.*; Austin, M. E.*; Bass, E. M.*; Budny, R.*; Heidbrink, W. W.*; Hillesheim, J. C.*; Holcomb, C. T.*; Gorelenkova, M.*; Grierson, B. A.*; McCune, D. C.*; Mckee, G. R.*; Muscatello, C. M.*; Park, J. M.*; Petty, C. C.*; Rhodes, T. L.*; Staebler, G. M.*; 鈴木 隆博; Van Zeeland, M. A.*; Waltz, R. E.*; Wang, G.*; White, A. E.*; Yan, Z.*; Yuan, X.*; Zhu, Y. B.*

Pace, D. C.*; Austin, M. E.*; Bass, E. M.*; Budny, R.*; Heidbrink, W. W.*; Hillesheim, J. C.*; Holcomb, C. T.*; Gorelenkova, M.*; Grierson, B. A.*; McCune, D. C.*; Mckee, G. R.*; Muscatello, C. M.*; Park, J. M.*; Petty, C. C.*; Rhodes, T. L.*; Staebler, G. M.*; Suzuki, Takahiro; Van Zeeland, M. A.*; Waltz, R. E.*; Wang, G.*; White, A. E.*; Yan, Z.*; Yuan, X.*; Zhu, Y. B.*

DIII-Dトカマクにおいて微視的乱流による高速イオンの輸送を中性粒子ビーム(NB)入射により調べた。背景の微視的乱流を特徴づけるパラメータ(Eb/Te値、Ebは入射エネルギー、Teは電子温度)を変化させるために、中心部または周辺部入射を行った。いずれの場合も、微視的乱流による輸送の増加は小さく実験的には観測できなかった。微視的乱流による高速イオンの拡散を数値的・解析的に評価し、高速イオンの輸送の効果をモデル化した。その結果、コヒーレントなモードによる高速イオンの輸送とNB電流駆動の低下の方が乱流輸送によるものより大きく、ITERにとってより重要であることがわかった。

Energetic ion transport due to microturbulence is investigated in MHD-quiescent plasmas by way of neutral beam injection in the DIII-D tokamak. A range of on-axis and off-axis beam injection scenarios are employed to vary relevant parameters such as the character of the background microturbulence and the value of Eb/Te, where Eb is the energetic ion energy and Te the electron temperature. In all cases it is found that any transport enhancement due to microturbulence is too small to observe experimentally. These transport effects are modeled using numerical and analytic expectations that calculate the energetic ion diffusivity due to microturbulence. It is determined that energetic ion transport due to coherent modes, including possible reductions in neutral beam current drive, is a considerably larger effect and should therefore be considered more important for ITER.