Measurements, modelling and electron cyclotron heating modification of Alfven eigenmode activity in DIII-D

Journal Article · Wed Dec 31 23:00:00 EST 2008 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/49/6/065003· OSTI ID:1015754

Van Zeeland, Michael ^[1]; Heidbrink, W. ^[2]; Nazikian, Raffi ^[3]; Austin, M. E. ^[4]; Cheng, C Z ^[5]; Chu, M. S. ^[6]; Gorelenkov, Nikolai ^[3]; Holcomb, C T ^[7]; Hyatt, A. W. ^[6]; Kramer, G. ^[3]; Lohr, J. T. ^[6]; Mckee, G. R. ^[8]; Petty, C C. ^[6]; Prater, R. ^[1]; Solomon, W. M. ^[3]; Spong, Donald A ^[9]

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1. General Atomics
2. University of California, Irvine
3. Princeton Plasma Physics Laboratory (PPPL)
4. University of Texas, Austin
5. National Cheng Kung University, Tainan, Taiwan
6. General Atomics, San Diego
7. Lawrence Livermore National Laboratory (LLNL)
8. University of Wisconsin, Madison
9. ORNL

Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including toroidicity and ellipticity induced Alfven eigenmodes (TAE/EAE, respectively) and reversed shear Alfven eigenmodes (RSAE) as well as their spatial coupling. These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. It is found that ideal MHD modelling of eigenmode spectral evolution, coupling and structure are in excellent agreement with experimental measurements. It is also found that higher radial envelope harmonic RSAEs are clearly observed and agree with modelling. Some discrepancies with modelling such as that due to up/down eigenmode asymmetries are also pointed out. Concomitant with the Alfvenic activity, fast ion (FIDA) spectroscopy shows large reductions in the central fast ion profile, the degree of which depends on the Alfven eigenmode amplitude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. The sensitivity of this effect to deposition power and current drive phasing as well as ECH modulation are presented.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1015754
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 6 Vol. 49; ISSN 0029-5515
• Country of Publication: United States
• Language: English