Advances in High Harmonic Fast Wave Heating of NSTX H-mode Plasmas

Conference · Fri Jan 01 00:00:00 EST 2010

OSTI ID:1111437

Ryan, Philip Michael ^[1]; Ahn, Joonwook ^[1]; Bell, R. E. ^[2]; Bonoli, P. ^[3]; Chen, Guangye ^[1]; Green, David L ^[1]; Harvey, R. W. ^[4]; Hosea, J. ^[2]; Jaeger, Erwin Frederick ^[1]; Kaye, S. ^[2]; LeBlanc, B ^[2]; Maingi, Rajesh ^[1]; Phillips, Cynthia ^[2]; Podesta, M. ^[2]; Taylor, G. ^[2]; Wilgen, John B ^[1]; Wilson, J. R. ^[2]

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1. ORNL
2. Princeton Plasma Physics Laboratory (PPPL)
3. Massachusetts Institute of Technology (MIT)
4. CompX, Del Mar, CA

High-harmonic fast wave (HHFW) heating and current drive is being developed in NSTX to provide bulk electron heating and q(0) control during non-inductively sustained Hmode plasmas fuelled by deuterium neutral-beam injection (NBI). In addition, it is used to assist the plasma current ramp-up. A major modification to increase the RF power limit was made in 2009; the original end-grounded, single end-powered current straps of the 12- element array were replaced with center-grounded, double end-powered straps. Greater than 3 MW have been coupled into NBI-driven, ELMy H-mode plasmas with this upgraded antenna. Improved core HHFW heating, particularly at longer wavelengths and during low-density start-up and plasma current ramp-up, has been obtained by lowering the edge density with lithium wall conditioning, thereby moving the critical density for fast-wave propagation away from the vessel wall [1]. Significant core electron heating of NBI-fuelled H-modes has been observed for the first time over a range of launched wavelengths and H-modes can be accessed by HHFW alone. Visible and IR camera images of the antenna and divertor indicate that fast wave interactions can deposit considerable RF energy on the outboard divertor plate, especially at longer wavelengths that begin to propagate closer to the vessel walls. Edge power loss can also arise from HHFWgenerated parametric decay instabilities; edge ion heating is observed that is wavelength dependent. During plasmas where HHFW is combined with NBI, there is a significant enhancement in neutron rate, and fast-ion D-alpha (FIDA) emission measurements clearly show broadening of the fast-ion profile in the plasma core. Large edge localized modes (ELMs) have been observed immediately following the termination of RF power, whether the power turn off is programmed or due to antenna arcing. Causality has not been established but new experiments are planned and will be reported. Fast digitization of the reflected power signal indicates a much faster rise time for arcs than for ELMs. Based on this observation, an ELM/arc discrimination system is being implemented to maintain RF power during ELMs even when the reflection coefficient becomes large. This work is supported by US DOE contracts DE-AC-05-00OR22725 and DE-AC02- 09CH11466. References [1] C. K. Phillips, et al, Nuclear Fusion 10, 075015 (2009)

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1111437
• Resource Relation: Conference: European Physical Society 37th Conference on Plasma Physics, Dublin, Ireland, 20100621, 20100625
• Country of Publication: United States
• Language: English