1 Electron Bernstein Wave Physics on NSTX - Taylor Electron Bernstein Wave Physics on NSTX G. Taylor, J.B. Caughman, M.D. Carter, S. Diem, P.C. Efthimion, R.W. Harvey, J. Preinhaelter, J.B. Wilgen, A. Bers, T.S. Bigelow, J. Decker, R.A. Ellis, N.M. Ershov, E. Fredd, J. Hosea, F. Jaeger, A.K. Ram, D.A. Rasmussen, A.P. Smirnov, J. Urban, J.R. Wilson 47 th APS – DPP Meeting Oct 24-28, 2005 Denver, Co. Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin Supported by Office of Science

2 Electron Bernstein Wave Physics on NSTX - Taylor EBWCD Can Stabilize and Sustain Non-Inductive High  Spherical Torus (ST) Plasmas Deposition similar for 14 GHz & 28 GHz and  ~ 20-40% Large trapped particle fraction on low field side of STs enables efficient off-axis Ohkawa EBWCD for GHz EBWs NSTX,  ~ 40%, B t (0) = 3.5 kG CQL3D/GENRAY Total Bootstrap NBCD J // (A/Wb) C. Kessel, Invited Talk UI , Fri AM RFCD Tokamak Simulation Code Need resilient coupling to EBWs NSTX B t (0) = 3.5 kG Need ~100 kA of I p driven by RF between  = 0.4 &  = 0.8 G. Taylor, et al., Phys. Plasmas 11, 4733 (2004) A.K. Ram, Invited Talk QI , Thurs AM Parallel Current Density (arb. Units) Current Density (A/cm 2 ) 

3 Electron Bernstein Wave Physics on NSTX - Taylor, Poster RP Thurs PM J. Caughman, Poster RP Thurs PM Measured GHz EBW Emission this Year to Assess EBW Coupling Efficiency AORSA-1D full wave code predicts efficient EBW coupling at ~ 28 GHz into  ~ 40% NSTX plasmas via oblique O-X-B launch (n // ~ ± 0.5) into  ~ 40% NSTX plasmas via oblique O-X-B launch (n // ~ ± 0.5) EBW coupling efficiency sensitive to edge conditions; EBW emission EBW coupling efficiency sensitive to edge conditions; EBW emission studies can assess EBW coupling efficiency: studies can assess EBW coupling efficiency: - cannot test parametric decay or ponderomotive effects M. Carter ORNL AORSA-1D NSTX  = 40% B t (0) = 3.5 kG f = 28 GHz

4 Electron Bernstein Wave Physics on NSTX - Taylor Measured 80% EBW Coupling at GHz via B-X-O Coupling Last Year, Consistent with Modeling, Phys. Plasmas 12, (2005) G. Taylor et al., Phys. Plasmas 12, (2005) J. Preinhaelter et al., AIP Proc. 787, 349 (2005) 3-D ray tracing & full wave EBW mode conversion model using EFIT magnetic equilibrium & Thomson scattering T e & n e f =16.5 GHz NSTX Shot Frequency = 16.5 GHz, B t (0) = 4.5 kG

5 Electron Bernstein Wave Physics on NSTX - Taylor Evolution of Measured GHz EBW Emission Similar to Simulation, but T rad ~ 2-4 Times Smaller

6 Electron Bernstein Wave Physics on NSTX - Taylor Measured T rad at 25 GHz Comes from Both 2f ce Near Axis, & 3f ce Off-axis; Harmonic Mix Sensitive to EBW n // Radial access between Radial access between 2f ce & 3f ce sensitive to 2f ce & 3f ce sensitive to EBW n // due to EC EBW n // due to EC resonance Doppler resonance Doppler broadening broadening Poster RP Thurs PM J. Preinhaelter Poster RP Thurs PM EBW Ray Tracing

7 Electron Bernstein Wave Physics on NSTX - Taylor Collisional Loss at Upper Hybrid Resonance (UHR) May Explain Low Measured EBW T rad T e ~ eV near UHR T e ~ eV near UHR Collisional losses can be Collisional losses can be significant for T e < 30 eV significant for T e < 30 eV EBW conversion efficiency EBW conversion efficiency sensitive to Z eff at low T e sensitive to Z eff at low T e Large uncertainty in Thomson Large uncertainty in Thomson scattering T e near UHR: scattering T e near UHR: - few data points available - few data points available near UHR for simulation near UHR for simulation Measured emission polarization Measured emission polarization consistent with simulation consistent with simulation Measured T rad Simulated T rad with Z eff = 0 at UHR Simulated T rad with Z eff = 3 at UHR Simulated T rad with Z eff = 5 at UHR Shot = Frequency = 25 GHz Measured Emission Polarization (E para/ E perp ) T rad (keV ) Polarization From Simulation 1000 Time (s )

8 Electron Bernstein Wave Physics on NSTX - Taylor Off-Axis RF CD Critical to Sustained High  ST Operation EBWCD efficiently generates needed off-axis current Efficient EBW coupling predicted via oblique O-mode launch EBW emission used to test coupling predictions on NSTX Radial access between 2f ce & 3f ce sensitive to EBW n // spectrum When T e < 30 ev at UHR collisional losses may reduce EBW coupling efficiency: - more significant issue for coupling between f ce & 2f ce

9 Electron Bernstein Wave Physics on NSTX - Taylor Future Work Remotely-steered 8-18 GHz & GHz B-X-O antennas being installed on NSTX for next run campaign Detailed study of EBW B-X-O coupling in L-mode & H-mode Integrate GENRAY/CQL3D EBW modeling into TRANSP & evaluate effect of transport on EBWCD EBWCD benchmarking between GENRAY/CQL3D & BANDIT (Culham, UK) began earlier this year for  = 40% NSTX plasma : - BANDIT & GENRAY predict Ohkawa EBWCD at r/a ~ BANDIT: 26 kA/MW - GENRAY/CQL3D: 37 kA/MW - Further work needed to refine benchmarking