Abstract Details

Presentation:submitted:by:
icc06_taylor_ebw_022706.pdf2006-02-27 08:29:26Gary Taylor

Electron Bernstein Wave Physics in NSTX and PEGASUS

Author: Gary Taylor
Submitted: 2005-12-19 14:10:10

Co-authors: S. DIEM, P.C. EFTHIMION, R.A. ELLIS, E. FREDD, J. HOSEA, B. LEBLANC, C.K. PHILLIPS, J.R. WILSON, G.D. GARSTKA, R.J. FONCK, B.T. LEWICKI, T.S. BIGELOW, M.D. CARTER, J.B. CAUGHMAN, F. JAEGER, D.A. RASMUSSEN, J.B. WILGEN, R.W. HARVEY, A.P. SMIRNOV, N.M. ERSH

Contact Info:
Princeton University
PO Box 451
Princeton, New Jersey   08543
USA

Abstract Text:
Off-axis EBWCD may be critical to sustaining solenoid-free high β spherical torus (ST) plasmas. Fokker-Planck and 3-D EBW ray-tracing models [1-3], together with EBW emission diagnostics [4] are being employed to study electron Bernstein wave (EBW) coupling, propagation and damping physics in NSTX. This research supports the design of a 4 MW, 28 GHz EBW current drive (EBWCD) system planned for NSTX. Modeling and emission measurements support efficient EBW coupling via obliquely launched O-mode polarized electromagnetic waves and the efficient generation of EBW-driven current via Ohkawa [5] current drive in a region of the ST plasma dominated by magnetically-trapped electrons. Intrinsic Doppler broadening of EBWs in the plasma may preclude core access at 28 GHz, however the off-axis EBWCD needed to support sustained high β operation in NSTX appears viable. EBWCD modeling of NSTX plasmas with β between 20% and 40% and EBW launch frequencies between 14 GHz and 28 GHz predicts current drive efficiencies of 40-50 kA/MW and EBW-driven current densities that peak at a normalized minor radius ~ 0.7 on the outboard side of the magnetic axis [1]. The EBW coupling efficiency at 16-18 GHz was measured to be 80±20%, in agreement with modeling [4]. The very-low-aspect ratio PEGASUS ST experiment provides an attractive opportunity to investigate 2.45 GHz EBW heating and current drive physics in an overdense ST plasma, prior to installation of a high power 28 GHz EBWCD system on NSTX. Numerical modeling of EBW propagation and damping in PEGASUS has been explored using EBW ray tracing and Fokker-Planck codes. Calculations predict 60 kA/MW in high Te plasmas. RF-driven current densities reached 20-100 kA/cm2 near the magnetic axis. Current drive was primarily via the Fisch-Boozer current drive mechanism [6]. Experiments with up to 1 MW of 2.45 GHz power will address fundamental issues concerning EBWs in ST experiments. These include edge coupling, nonlinear effects at the edge such as parametric instabilities, ray propagation, deposition and EBWCD efficiency.
[1] G. Taylor, et al., Phys. Plasmas 11, 4733 (2004)
[2] R.W. Harvey and G. Taylor, Phys. Plasmas 12, 051509 (2005)
[3] J. Preinhaelter, et al., “EBW Simulation for MAST and NSTX Experiments?, p. 349 AIP Conference Proceedings 787, 349 (2005)
[4] G. Taylor, et al., Phys. Plasmas 12, 052511 (2005)
[5] T. Ohkawa, General Atomics Report No. GA-A13847 (1976)
[6] N.J. Fisch and A. Boozer, Phys. Rev. Lett. 45, 720 (1980)
*Supported by U.S. DOE Contracts DE-AC02-76CH03073, DE-FG02-96ER54375 and DE-FG03-02ER54684

Characterization: A3

Comments:
My author list was truncated by your submisson program additional authors are:
N.M. ERSHOV, J. URBAN, J. PREINHAELTER, A.K. RAM

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