Loading...
Please wait, while we are loading the content...
Similar Documents
Characterization of neo-classical tearing modes in high-performance I-mode plasmas with ICRF mode conversion flow drive on Alcator C-Mod
| Content Provider | Semantic Scholar |
|---|---|
| Author | Lin, Yijun Granetz, Robert S. Reinke, M. L. Rice, Jeremy Wolfe, S. M. Wukitch, Stephen James |
| Copyright Year | 2012 |
| Abstract | Neo-classical tearing modes (NTMs) have been observed on Alcator C-Mod. The NTMs occur in high performance I-mode plasmas that are heated by a combination of ICRF D(H) minority heating at 80 MHz and D(He) mode conversion (MC) heating at 50 MHz. I-mode plasmas have confinement as good as H-mode but lower collisionality. Due to the stabilizing effect by the energetic minority hydrogen ions, long sawtooth (≥ 40 ms) and large sawtooth crashes (∆Te0 ≥ 3 keV) are produced in these hot (Te ≤ 9 keV) plasmas. A typical case is that soon after the plasma enters I-mode, a (m = 4, n = 3) mode (f = 40-60 kHz) appears following a large sawtooth crash, and then a (3, 2) mode (20-40 kHz) appears later at slightly higher βN. The (3, 2) mode can also occur without a preceding (4, 3) mode. In some plasmas, a (2, 1) mode may appear simultaneously with the (3, 2) mode, and lead to disruption. The onset criterion of the (3, 2) NTMs approximately follows that obtained from DIII-D and ASDEX Upgrade. The onset parameters are βP ~ 0.4-0.7, βN ~ 1.0-1.4, βN/ρi* ~ 200-350, νNTM (q=3/2) ~ 0.04-0.25. The saturated magnetic island width of the (4, 3) mode is typically Wsat ~ 0.4-0.6 cm, and the mode usually has an insignificant effect on confinement. For the (3, 2) mode, Wsat ~ 0.8-1 cm, which is 3-4 times the ion banana width, and the mode can cause small confinement degradation (∆β/β ~ a few percent). The NTMs have a strong effect on plasma rotation. MC flow drive generates large toroidal rotation above 100 km/sec in L-mode, and when the plasma enters I-mode, plasma rotation is expected to increase significantly due to the additional intrinsic rotation torque from the edge Te pedestal. However, the rotation almost always stops rising after the onset of the NTM(s). The appearance of the (3, 2) mode usually rapidly reduces the rotation speed, and the (2, 1) mode, if occurs, would completely halt the rotation. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www1.psfc.mit.edu/research/alcator/pubs/iaea/2012/LinY_IAEA_2012_paper_EXP4-22.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
