Electron Bernstein Wave (EBW) Physics In NSTX and PEGASUS

Transcription

1 Electron Bernstein Wave (EBW) Physics In NSTX and PEGASUS G. Taylor 1, J.B. Caughman 2, M.D. Carter 2, S. Diem 1, P.C. Efthimion 1, R.W. Harvey 3, J. Preinhaelter 4, J.B. Wilgen 2, T.S. Bigelow 2, R.A. Ellis 1, N.M. Ershov 5, R.J. Fonck 6, E. Fredd 1, G.D. Garstka 6, J. Hosea 1, F. Jaeger 2, B.P. LeBlanc 1, B.T. Lewicki 6, C.K. Phillips 1, A.K. Ram 7, D.A. Rasmussen 2, A.P. Smirnov 5, J. Urban 4, J.R. Wilson 1 1 Princeton University 2 Oak Ridge National Laboratory 3 CompX 4 Czech Institute of Plasma Physics 5 Moscow State University 6 University of Wisconsin-Madison 7 Massachusetts Institute of Technology Innovative Confinement Concepts Workshop February 13-16, 26 Austin, Texas EBW Physics in NSTX and Pegasus 1

2 Outline Importance of EBWs to Spherical Torus Plasma Research EBW Current Drive Modeling Results for NSTX EBW Coupling Research on NSTX Plans for EBW Heating & Current Drive on PEGASUSP Summary 2

3 Outline Importance of EBWs to Spherical Torus Plasma Research EBW Current Drive Modeling Results for NSTX EBW Coupling Research on NSTX Plans for EBW Heating & Current Drive on PEGASUSP Summary 3

4 Major NSTX Research Goal to Sustain β ~ 4% Without Using Central Solenoid R a I p B t T e () n e () 85 cm 68 cm ~ 1 MA T ~ 1 kev.2-1x cm -3 NBI ~ 7 MW, P HHFW ~ 6 MW P NBI NSTX operates at up to: Plasma Pressure Magnetic Pressure β = ~ 4% 4

5 ~1 ka of Off-Axis RF-Driven Current Needed to Sustain Solenoid-Free β ~ 4% NSTX Plasmas Parallel Current Density [per unit poloidal flux change] (A/Wb) 1 6 NSTX, β t = 42%, β pol = 1.6 B t =.34 T, I p = 1 MA NBCD Total Bootstrap RFCD.5 1 r/a ρ Modeling of solenoid-free, β ~ 4% NSTX plasmas predicts bootstrap & NBI CD can provide only ~ 9% of plasma current Need ~ 1 ka of rf-driven Current between.4 < r/a <.8 Charles Kessel (PPPL) Tokamak Simulation C ode 5

6 NSTX Plasmas Overdense (f pe >> f ce ) Cannot Use Electron Cyclotron Heating & Current Drive Characteristic Frequencies on NSTX Midplane at β = 41% Axis Last Closed Flux Surface 5 4 f UHR 6fce 3 Frequency (GHz) GHz 3f ce 2f ce 14 GHz f ce 5f ce 4f ce Major Radius (m) 6

7 Studying EBW Thermal Emission (EBE) Allows Measurement of EBW Coupling to Electromagnetic Waves EBWs Propagate in Overdense Plasmas Exhibit Strong Absorption & Emission at Electron Cyclotron Resonances Cannot propagate outside upper hybrid resonance surrounding overdense plasma CL f ce ECR UHR Can couple to X-mode (B-X) or O-mode (B-X-O) electromagnetic waves EBE coupling measurements do not test high power parametric or ponderomotive effects EBW Major Radius X-mode EM Waves 7

8 Oblique O-X-B Coupling Can Enable Direct Coupling to EBWs without Tunneling Upper Hybrid Resonance EBW Slow X-Mode O-Mode Electromagnetic Antenna.6 1 B-X-O Coupling (%) n pol RF power launched oblique to magnetic field Angular coupling window depends on L n at conversion layer, but less sensitive to L n than X-B coupling n tor.6 8

9 Outline Importance of EBWs to Spherical Torus Plasma Research EBW Current Drive Modeling Results for NSTX EBW Coupling Research on NSTX Plans for EBW Heating & Current Drive on PEGASUSP Summary 9

10 Efficient EBWCD Predicted in NSTX Plasmas in Region with Large Trapped Electron Fraction Deposition similar for 14 GHz & 28 GHz and β ~ 2-4% CQL3D/GENRAY Current Density (A/cm 2 ) NSTX B t () = 3.5 kg GENRAY ray tracing and CQL3D Fokker- Planck codes used to model NSTX EBWCD G. Taylor, et al., Phys. Plasmas 11,, 4733 (24) 1

11 Strong Diffusion Near Trapped-Passing Boundary Enables Efficient Ohkawa EBWCD 1 Contours of Quasilinear RF Velocity Space Diffusion Operator U norm = 3 kev! =.7 G ENRAY/CQ L3D U /U perp /U norm norm Electron Diffusion Trapped-Passing Boundary -1 1 U U para /U norm 11

12 Normalized EBWCD Efficiency (ζ ec ) Increases with r/a on Low Field Side of Axis G ENRAY/CQ L3D ζ ec = 3.27 x I p (A) x R(m) x n e (1 19 T e (kev)) x P(W) 19 m -3 ) NSTX Frequency = 15 GHz Power = 1 MW C.C. Petty, AIP Proc. 595,, 275 (21) R 12

13 Synergy with Bootstrap Current Modifies EBWCD Current Profile & Enhances CD Efficiency by ~ 1% EBW Power = 1 MW, Co-Current Drive 15 EBWCD + Synergy Bootstrap Current 1 Parallel Current Density J(A/cm 2 ) 5 EBWCD Current.2.4 Normalized Radius,! R.W. Harvey & G. Taylor, Phys. Plasmas 12,, 5159 (25) -5. Synergy Bootstrap Current.6 G ENRAY/CQ L3D Synergistic bootstrap current increase due to EBW-induced pitch angle scattering across trapped-passing boundary Trapped particle pinch, that may reduce EBWCD efficiency, is not included

14 Outline Importance of EBWs to Spherical Torus Plasma Research EBW Current Drive Modeling Results for NSTX EBW Coupling Research on NSTX Plans for EBW Heating & Current Drive on PEGASUSP Summary 14

15 Measured 8% B-X-O Coupling in L-Mode Edge Plasmas, Consistent with Modeling T rad & T e (kev).5 R (m) T e of EBW Emission Layer NSTX Shot NSTX Shot EBW Frequency = 16.5 GHz Frequency = 16.5 GHz, B t () = 4.5 kg R axis Calculated EBW T rad R LCFS Radius of EBW Emission Layer Time-Averaged Measured EBW T rad.3.6 TIME (s) G. Taylor et al., Phys. Plasmas 12,, (25) J. Preinhaelter et al., AIP Proc. 787,, 349 (25) k perp 1 EB W Z(m) Slow X-Mode f =16.5 GHz.4 f ce LCFS x L x O Upper -1 Hybrid Resonance UHR 2f ce EBW Rays O-Mode Radius 2f ce R(m) 1.6 Electromagnetic Antenna 3-D ray tracing & full wave EBW mode conversion model using EFIT magnetic equilibrium & Thomson scattering T e & n e 15

16 ~ 3% B-X-O Coupling in H-Modes; Coupling Reduced by EBW Damping at Upper Hybrid Resonance (UHR) 1 Shot = f = 25 GHz Measured T rad Simulated T rad with Z eff = 3 at UHR Simulated T rad with Z eff = 5 at UHR Simulated T rad with no EBW damping at UHR 6 4 Freq. (GHz) 25 GHz 2 Axis T e Last Closed Flux Surface 2f ce f UHR 3f ce 1. T e (kev) T rad (kev) Time.6 (s) R(m) T e ~ 2 ev at UHR, near foot of H-mode pedestal EBW collisional damping sensitive to Z eff for T e < 3 ev Measured EBE probably only from 3f ce off-axis where T e ~ 6eV 16

17 Remotely-steered B-X-O Antennas, Covering 8-4 GHz, will Test EBW Coupling Efficiency Predictions from Models Dual Channel 18-4 GHz Radiometer Lens 18-4 GHz Quad Ridged Antenna Plasma EBW Emission Vacuum Windows Lens 8-18 GHz Quad Ridged Antenna Dual Channel 8-18 GHz Radiometer Experiments will study L- & H-mode plasmas and effect of Li pumping on EBW edge coupling Scanning frequency & antenna viewing angle provides key information on angle of peak EBW coupling & emission polarization EBW coupling study critical for assessing technical feasibility of EBWCD Supports EBW T e (R,t) diagnostic development AORSA-1D NSTX β = 4% B t () = 3.5 kg f = 28 GHz M. Carter ORNL 17

18 Outline Importance of EBWs to Spherical Torus Plasma Research EBW Current Drive Modeling Results for NSTX EBW Coupling Research on NSTX Plans for EBW Heating & Current Drive on PEGASUSP Summary 18

19 2.45 GHz EBW Experiments on PEGASUSP will Study Coupling, Propagation, Heating & CD Existing 2.45 GHz PLT equipment used for planned.9 MW EBW system Demonstrate EBW coupling at significant power via O-X-B & X-B Study nonlinear EBW coupling effects Validate ray tracing, demonstrate electron heating Measure EBWCD 19

20 Near Midplane EBW Launch Provides Optimal Electron Heating Near Axis GENRAY ray tracing & CQL3D Fokker-Planck codes used to model EBW propagation, damping & CD in PEGASUSP EBWs damping near axis results in localized heating Energy damped in smaller plasma volume leads to maximized heating Rod Current 12 9 ka Peak 12 ka Power 8 Power 15 ka 8 Density Density (W/cm2) (W/cm2) P 4 rf = 2 kw 4 Pol. Launch Angle = 15 o P rf = 2 kw Poloidal Location of EBW Launcher (deg.) Normalized Minor Radius 2

21 Near Midplane EBW Launch Maximizes EBW-Driven Current EBWs can be used to tailor current profile Can be used to affect tearing mode stability Maximize pressure driven current (I BS ) Current Density (ka/cm2) Rod Current 9 ka 12 ka 15 ka P rf = 2 kw Poloidal Location of EBW Launcher (deg.) 21

22 Fisch-Boozer CD Dominant for Near-Midplane EBW Launch v (u/v norm ) v (u/v norm ) Electron Distribution Quasilinear Diffusion v (u/v norm ) Rod Current = 12 ka Antenna at Pol. Angle = 15 deg. ρ =.1, near peak EBWCD Quasilinear diffusion coefficient peaks in passing electron region Preferential heating of electrons with negative v 22

23 Outline Importance of EBWs to Spherical Torus Plasma Research EBW Current Drive Modeling Results for NSTX EBW Coupling Research on NSTX Plans for EBW Heating & Current Drive on PEGASUSP Summary 23

24 EBWCD Critical for Enabling Non-Inductively Sustained ST Operation at High β Ohkawa EBWCD predicted to efficiently generate off-axis current at high β in NSTX 3 MW of 28 GHz EBW power sufficient to drive ~ 1 ka needed to sustain β ~ 4% in NSTX ~ 8% EBW coupling via oblique O-mode antenna demonstrated on NSTX; EBW damping at UHR can reduce coupling from H-modes EGASUS.9 MW, 2.45 GHz EBW system will study high power coupling, electron heating and current drive PEGASUS 24