| Issue |
EPL
Volume 116, Number 4, November 2016
|
|
|---|---|---|
| Article Number | 45003 | |
| Number of page(s) | 5 | |
| Section | Physics of Gases, Plasmas and Electric Discharges | |
| DOI | https://doi.org/10.1209/0295-5075/116/45003 | |
| Published online | 09 January 2017 | |
Alfvénic ion temperature gradient activities in a weak magnetic shear plasma
1 Southwestern Institute of Physics - P.O. Box 432 Chengdu 610041, China
2 Institute for Fusion Theory and Simulation, Zhejiang Univ. - Hangzhou 310027, China
3 School of Physics and Optoelectronic, DUT - Dalian 116024, China
Received: 17 November 2016
Accepted: 20 December 2016
We report the first experimental evidence of Alfvénic ion temperature gradient (AITG) modes in HL-2A Ohmic plasmas. A group of oscillations with 
and 
is detected by various diagnostics in high-density Ohmic regimes. They appear in the plasmas with peaked density profiles and weak magnetic shear, which indicates that corresponding instabilities are excited by pressure gradients. The time trace of the fluctuation spectrogram can be either a frequency staircase, with different modes excited at different times or multiple modes may simultaneously coexist. Theoretical analyses by the extended generalized fishbone-like dispersion relation (GFLDR-E) reveal that mode frequencies scale with ion diamagnetic drift frequency and 
, and they lie in KBM-AITG-BAE frequency ranges. AITG modes are most unstable when the magnetic shear is small in low pressure gradient regions. Numerical solutions of the AITG/KBM equation also shed light on why AITG modes can be unstable for weak shear and low pressure gradients. It is worth emphasizing that these instabilities may be linked to the internal transport barrier (ITB) and H-mode pedestal physics for weak magnetic shear.
PACS: 52.35.Bj – Magnetohydrodynamic waves (e.g., Alfven waves) / 52.35.Py – Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.) / 52.35.Mw – Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
© EPLA, 2016
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