Transition from chirping to steady NBI-driven Alfvén modes caused by magnetic configuration variations in the TJ-II stellarator. (3rd June 2016)

• Record Type: Journal Article
• Authors: Melnikov, A.V.; Eliseev, L.G.; Ascasíbar, E.; Cappa, A.; Castejón, F.; Hidalgo, C.; Ido, T.; Jiménez, J.A.; Kozachek, A.S.; Krupnik, L.I.; Liniers, M.; Lysenko, S.E.; Nagaoka, K.; de Pablos, J.L.; Shimizu, A.; Sharapov, S.E.; Ufimtsev, M.V.; Yamamoto, S.
• Other Names: collab.; collab.
• Is Part Of: Nuclear fusion. Volume 56:Number 7(2016:Jul.)
• Publication Date: 2016-06-03
• Subjects: Alfvén eigenmodes -- chirping -- TJ-II stellarator -- HIBP; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/56/7/076001
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac ( B 0 = 0.95 T, 〈 R 〉 = 1.5 m, 〈 a 〉 = 0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating ( P NBI ⩽ 1.0 MW, E NBI = 32 keV, P ECRH ⩽ 0.6 MW). In low-density plasmas in the range n e ¯ = (0.3–1.5) × 10 19 m −3, a large variety of AEs have been observed in the plasma core with the heavy ion beam probe diagnostic and Mirnov coils, in the frequency range 50 kHz < f AE < 380 kHz. In experiments in which the vacuum rotational transform ι is varied during the shot (dynamic configuration scan), some AEs exhibit changes in their nonlinear evolution from bursting-amplitude AEs with chirping frequency to steady-frequency AEs, and back. The range of ι intervals within which the AEs studied are chirping or steady-state is determined.