Electron-cyclotron-resonance heating in Wendelstein 7-X: A versatile heating and current-drive method and a tool for in-depth physics studies

• Published in: Plasma physics and controlled fusion Vol. 61; no. 1; pp. 14037 - 14045
• Main Authors: Wolf, R C, Bozhenkov, S, Dinklage, A, Fuchert, G, Kazakov, Y O, Laqua, H P, Marsen, S, Marushchenko, N B, Stange, T, Zanini, M, Abramovic, I, Alonso, A, Baldzuhn, J, Beurskens, M, Beidler, C D, Braune, H, Brunner, K J, Chaudhary, N, Damm, H, Drewelow, P, Gantenbein, G, Gao, Yu, Geiger, J, Hirsch, M, Höfel, U, Jakubowski, M, Jelonnek, J, Jensen, T, Kasparek, W, Knauer, J, Korsholm, S B, Langenberg, A, Lechte, C, Leipold, F, Mora, H Trimino, Neuner, U, Nielsen, S K, Moseev, D, Oosterbeek, H, Pablant, N, Pasch, E, Plaum, B, Pedersen, T Sunn, Sitjes, A Puig, Rahbarnia, K, Rasmussen, J, Salewski, M, Schilling, J, Scott, E, Stejner, M, Thomsen, H, Thumm, M, Turkin, Y, Wilde, F
• Format: Journal Article
• Language: English
• Published: United States IOP Publishing 01.01.2019; IOP Science
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Astrophysics; electron-cyclotron-resonance heating and current drive; Physics; stellarator; Wendelstein 7-X
• ISSN: 0741-3335; 1361-6587
• DOI: 10.1088/1361-6587/aaeab2

For stellarators, which need no or only small amounts of current drive, electron-cyclotron-resonance heating (ECRH) is a promising heating method even for the envisaged application in a fusion power plant. Wendelstein 7-X (W7-X) is equipped with a steady-state capable ECRH system, operating at 140 GHz, which corresponds to the 2nd cyclotron harmonic of the electrons at a magnetic field of 2.5 T. Ten gyrotrons are operational and already delivered 7 MW to W7-X plasmas. Combined with pellet injection, the highest triple product (0.68 × 1020 keV m−3 s), observed up to now in stellarators, was achieved (Sunn Pedersen et al 2018 Plasma Phys. Control. Fusion 61 014035). For the first time, W7-X plasmas were sustained by 2nd harmonic O-mode heating, approaching the collisionality regime for which W7-X was optimized. Power deposition scans did not show any indication of electron temperature profile resilience. In low-density, low-power plasmas a compensation of the bootstrap current with electron-cyclotron current drive (ECCD) was demonstrated. Sufficiently strong ECCD close to the plasma centre produced periodic internal plasma-crash events, which coincide with the appearance of low order rationals of the rotational transform.