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XP-720: EBW Coupling at 8-36 GHz in H-Mode Plasmas

XP-720: EBW Coupling at 8-36 GHz in H-Mode Plasmas. Steffi Diem Waves ET Meeting March 29 rd , 2007. Very Low B-X-O Coupling Measured During H-mode Plasmas in 2006. <10% coupling efficiency measured during I p flattop (after emission burst)

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XP-720: EBW Coupling at 8-36 GHz in H-Mode Plasmas

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  1. XP-720: EBW Coupling at 8-36 GHz in H-Mode Plasmas Steffi Diem Waves ET Meeting March 29rd, 2007

  2. Very Low B-X-O Coupling Measured During H-mode Plasmas in 2006 • <10% coupling efficiency measured during Ip flattop (after emission burst) • Emission unpolarized after t~0.25s, indicating diagnostic measuring scattered emission H-Mode Possible causes: collisional damping, edge bootstrap current effects

  3. Data Mining Suggests Reduced Emission May be Coupled to Z-Position • Emission burst occurs for z(0)>-2 cm and decays when z(0)<-2 cm • Possibly similar to results observed during EBW heating experiments on TCV 120910 121227 - decaying EBE 117970 - 30% [2005] 120910 - EBE burst

  4. Slowly Decaying EBE H-Mode Shot Observed • Emission slowly decays during discharge • Coupling efficiency drops from 40% to 15% • Antenna pointing direction not optimized • Similar to refraction effects observed on MAST • "Prospects of EBW Emission Diagnostics and EBW Heating in Spherical Tokamaks", V.F. Shevchenko, et. al. 121227 fce=15.5 GHz

  5. Low EBE During H-Mode will be Investigate During 2007 NSTX Run Campaign • Investigate collisional effects on B-X-O mode coupling • Li pellet injection will be used to modify edge Te and change collisionality at B-X-O mode conversion layer • Investigate effects of plasma parameters on B-X-O coupling • Bootstrap current from pressure gradient at H-mode pedestal may change field pitch at UHR: • Pitch may be large enough to move B-X-O emission window outside antenna acceptance angle • Install wide acceptance angle spiral antenna to detect EBE outside acceptance angle Research will support an invited talk at the 17th Topical Conference on RF in Plasmas on May 7-9th, 2007

  6. H-Mode Run Plan 2007 Campaign • Run plan (36 shots ~ 1 day) 1-5 Shot development of bursting EBE H-mode (122939) 6-7 Optimize antenna alignment 8 Reflectometer/reciprocating probe data shot Vertical position scan using rtEFIT: 9-10 - start with target discharge, move z(0) +2 to +3 cm 11 - repeat for reflectometer and reciprocating probe 12-13 - use rtEFIT to move vertical position +0 to +6 cm during Ip flattop 14-15 - start with target discharge, move z(0) -2 to -3 cm 16 - repeat for reflectometer and reciprocating probe 17-18 - use rtEFIT to move vertical position +0 to -6 cm during Ip flattop

  7. H-Mode Run Plan 2007 Campaign • Run plan (36 shots ~ 1 day) - continued Outer gap scan: 19-20 - Increase outer gap by +5 cm 21-22 - Increase outer gap by +10 cm 23-24 - Decrease outer gap to 5 cm Bootstrap current scan: 25-26- introduce later gas fueling during current flattop to increase edge collisionality 27-28 - starting with target discharge, increase k to 2.5 29-30 - starting with target discharge, TF ramp 4.5 to 5.5 kG 31-33 - add gas fueling, k~2.7, and TF ramp 4.5-5.5 kG 34 - repeat for reflectometer and reciprocating probe 35-36 - Introduce early H-L transition halfway through Ip flattop

  8. Diagnostic Requirements • EBW antennas • 8-18 GHz system • 18-36 GHz system • spiral antenna system • 30-point Thomson scattering • Magnetics (for EFIT) • Reflectometer (ORNL & UCLA) • Fast reciprocating probe • MSE

  9. Extra Slides

  10. Remotely Steered EBW Antennas Allow Angular Mapping of fce & 2 fce B-X-O Coupling Window Beam waist • ±10° scan in poloidal and • toroidal directions • Acceptance angle: • 8-18 GHz antenna ~ 22° • 18-40 GHz antenna ~ 14° Ln~3 cm Ln~7 cm Antenna spatial scan region

  11. 2006 Scan of H-Mode Window Indicates Very Low Emission • Target discharge: Ip~1MA, Te(0)~0.9 keV, ne(0)~5e13 m-3 • Burst of emission observed shortly after L-H transition 120910

  12. Slowly Decaying EBE H-Mode Shot Observed • Discharge characteristics: Ip=1MA, Te(0)~1keV, ne(0)~4e1013 m-3 Shot 121227 t=0.3 s

  13. Quiescent H-Mode from Previous Run Good Target Discharge • Fluctuation free edge • Steep edge gradients • Improve B-X-O coupling 117260

  14. H-L Transition May Provide Insight to Understanding B-X-O Coupling in H-Modes H-L • Event at t=0.35 s kills B-X-O emission For 2007 develop disruption-free discharge with H-L transition for bursting H-modes

  15. H-L Transition May Provide Insight to Understanding B-X-O Coupling in H-Modes • Discharge characteristics: Ip~750 kA, H-L transition at t~0.33s H-L 120217

  16. 120215 H-L t=0.42s t=0.3s

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