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HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas*

NSTX. Supported by. HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas*. Gary Taylor 1

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HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas*

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  1. NSTX Supported by HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas* Gary Taylor1 P. T. Bonoli2, D. L. Green3, R. W. Harvey4, J. C. Hosea1, E. F. Jaeger3, B. P. LeBlanc1, C. K. Phillips1, P. M. Ryan3, E. J. Valeo1, J. R. Wilson1, J. C. Wright2, and the NSTX Team 1Princeton Plasma Physics Laboratory, Princeton, NJ, USA 2MIT Plasma Science and Fusion Center, Cambridge, MA, USA 3Oak Ridge National Laboratory, Oak Ridge, TN, USA 4CompX, La Jolla, CA, USA 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 JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI NFRI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep Columbia U CompX General Atomics FIU INL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U ORNL PPPL Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Illinois U Maryland U Rochester U Washington U Wisconsin 19th Topical Conference on Radio Frequency Power in Plasmas Newport, Rhode Island, USA, June 1-3, 2011 *Work supported by US DoE contracts DE-AC02-09CH11466 and DE-AC05-00OR22725

  2. Outline • Introduction to HHFW Heating on NSTX • HHFW-Generated H-Mode Plasmas • HHFW Heating of NBI H-Mode Plasmas • Summary

  3. Outline • Introduction to HHFW Heating on NSTX • HHFW-Generated H-Mode Plasmas • HHFW Heating of NBI H-Mode Plasmas • Summary

  4. Outline • Introduction to HHFW Heating on NSTX • HHFW-Generated H-Mode Plasmas • HHFW Heating of NBI H-Mode Plasmas • Summary

  5. Outline • Introduction to HHFW Heating on NSTX • HHFW-Generated H-Mode Plasmas • HHFW Heating of NBI H-Mode Plasmas • Summary

  6. NSTX is a high b, low aspect ratio, spherical torus with both 90 keV NBI and 30 MHz HHFW heating • R = 0.86 m • A > 1.27 • Ip < 1.5 MA • Bt(0) = 0.55 T • bt ≤ 40%, bN ≤ 7 • 90 keV D PNBI ≤ 6 MW • 30 MHz PRF ≤ 6 MW • Many fast wave ion resonances: 7-11 WD • Strong single pass direct absorption on electrons

  7. Well defined antenna spectrum, ideal for studying phase dependence of heating & current drive (CD) 30 MHz Power Sources 5 Port Cubes Decoupler Elements 12 Antenna Straps B IP 12-strap antenna extends toroidally 90° • Upgraded from single to double feed straps, with center grounds, in 2009 to reduce electric fields near Faraday shield ~ 1.5 x for same strap currents P. M. Ryan, et al., Poster A32

  8. HHFW heating and CD are being developed for non-inductive ramp-up and bulk electron heating Non-Inductive Strategy IP [kA] • Two major roles for HHFW heating and CD in NSTX: • Enable fully non-inductive plasma current (Ip) ramp-up through bootstrap CD (BSCD) and direct RFCD during early HHFW H-mode • Provide bulk electron heating during Ip flat top, during NBI H-Mode ~ 750 ~ 500 ~ 300 H-mode Time HHFW + NBI HHFW Sustain with HHFW + NBI CHI, PF, Guns

  9. NSTX HHFW research in 2008-10 focused on studying both HHFW-Generated H-Modes & HHFW-Heated NBI H-modes • Near-term approach to assess HHFW heating during Ip ramp-up has been to heat low Ip ohmic (~ 300 kA) plasmas to access 100% non-inductive CD • Improved antenna/plasma conditioning produced HHFW-generated H-mode plasmas with Ip = 650 kA, BT(0) = 0.55 T when PRF ≥ 2.5 MW • NBI + HHFW H-mode experiments at Ip = 0.7 - 1 MA, aided by Li conditioning, produced significant bulk electron heating when HHFW was coupled into the plasma: • HHFW acceleration of NBI fast-ions produced enhanced fast-ion losses during HHFW heating • Conducted extensive studies of HHFW heating and edge power loss mechanisms during ELMing and ELM-free H-modes

  10. NSTX HHFW research in 2008-10 focused on studying HHFW-Generated H-Modes & HHFW-Heated NBI H-modes • Near-term approach to assess HHFW heating during Ip ramp-up has been to heat low Ip ohmic (~ 300 kA) plasmas to access 100% non-inductive CD • Improved antenna/plasma conditioning produced HHFW-generated H-mode plasmas with Ip = 650 kA, BT(0) = 0.55 T when PRF ≥ 2.5 MW • NBI + HHFW H-mode experiments at Ip = 0.7 - 1 MA, aided by Li conditioning, produced significant bulk electron heating when HHFW was coupled into the plasma: • HHFW acceleration of NBI fast-ions produced enhanced fast-ion losses during HHFW heating • Conducted extensive studies of HHFW heating and edge power loss mechanisms during ELMing and ELM-free H-modes

  11. NSTX HHFW research in 2008-10 focused on studying both HHFW-Generated H-Modes & HHFW-Heated NBI H-modes • Near-term approach to assess HHFW heating during Ip ramp-up has been to heat low Ip ohmic (~ 300 kA) plasmas to access 100% non-inductive CD • Improved antenna/plasma conditioning produced HHFW-generated H-mode plasmas with Ip = 650 kA, BT(0) = 0.55 T when PRF ≥ 2.5 MW • NBI + HHFW H-mode experiments at Ip = 0.7 - 1 MA, aided by Li conditioning, produced significant bulk electron heating when HHFW was coupled into the plasma: • HHFW acceleration of NBI fast-ions produced enhanced fast-ion losses during HHFW heating • Conducted extensive studies of HHFW heating and edge power loss mechanisms during ELMing and ELM-free H-modes

  12. NSTX HHFW research in 2008-10 focused on studying both HHFW-Generated H-Modes & HHFW-Heated NBI H-modes • Near-term approach to assess HHFW heating during Ip ramp-up has been to heat low Ip ohmic (~ 300 kA) plasmas to access 100% non-inductive CD • Improved antenna/plasma conditioning produced HHFW-generated H-mode plasmas with Ip = 650 kA, BT(0) = 0.55 T when PRF ≥ 2.5 MW • NBI + HHFW H-mode experiments at Ip = 0.7 - 1 MA, aided by Li conditioning, produced significant bulk electron heating when HHFW was coupled into the plasma: • However HHFW acceleration of NBI fast-ions produced enhanced fast-ion losses during HHFW heating • Conducted extensive studies of HHFW heating and edge power loss mechanisms during ELMing and ELM-free H-modes

  13. NSTX HHFW research in 2008-10 focused on studying both HHFW-Generated H-Modes & HHFW-Heated NBI H-modes • Near-term approach to assess HHFW heating during Ip ramp-up has been to heat low Ip ohmic (~ 300 kA) plasmas to access 100% non-inductive CD • Improved antenna/plasma conditioning produced HHFW-generated H-mode plasmas with Ip = 650 kA, BT(0) = 0.55 T when PRF ≥ 2.5 MW • NBI + HHFW H-mode experiments at Ip = 0.7 - 1 MA, aided by Li conditioning, produced significant bulk electron heating when HHFW was coupled into the plasma: • However HHFW acceleration of NBI fast-ions produced enhanced fast-ion losses during HHFW heating • Conducted extensive studies of HHFW heating and edge power loss mechanisms during both ELMing and ELM-free H-modes

  14. Non-Inductive Strategy IP [kA] HHFW-Generated H-Mode Plasmas ~ 750 ~ 500 ~ 300 H-mode Time HHFW + NBI HHFW Sustain with HHFW + NBI CHI, PF, Guns

  15. Achieved sustained Ip = 300 kA HHFW H-mode, with internal transport barrier (ITB) and Te(0) ~ 3 keV with PRF = 1.4 MW • In 2005 could not maintain RF coupling during Ip = 250 kA HHFW H-mode due to poor plasma position control at L-H transitions • Reduced plasma control system latency made possible sustained Ip = 300 kA HHFW-generated H-mode in 2010: • Te(0) ~ 3 keV achieved with only PRF = 1.4 MW • ITB formed during H-mode • Positive feedback between ITB, high Te(0) and RF CD Ip = 300 kA BT(0) = 0.55 T Deuterium kf = - 8 m-1 Te(0) ~ 3 keV Time of GENRAY-ADJ analysis

  16. GENRAY-ADJ predicts peaked RF deposition on electrons and RF CD efficiency xCD ~ 115 kA/MW Shot 138506 Time = 0.382 s IP = 300 kA BT = 5.5 kG Deuterium RF H-mode r/a IRFCD ~ 115 kA/MW GENRAY/ADJ-QL r/a

  17. TRANSP-TORIC simulation, assuming 100% RF coupling (heff = 100%), predicts IBootstrap = 220 kA and IRF = 120 kA TORIC-TRANSP modeling for heff = 100% Time of GENRAY-ADJ analysis • TRANSP-TORIC predicts xCD~ 85 kA/MW at GENRAY analysis time: • Compared to GENRAY xCD~ 115 kA/MW • heff = DWT/(t*PRF) • DWT ~ 15 kJ • t ~ 15 ms • PRF~ 1.4 MW •  heff ~ 60%

  18. 80% of the non-inductive current is generated inside the ITB in the Ip = 300 kA HHFW H-mode TORIC-TRANSP modeling for heff = 100% For heff = 60%

  19. Improved antenna conditioning produced ELM-free-like HHFW H-modes at Ip = 650 kA with PRF ≥ 2.5 MW He, kf = - 8 m-1 Ip = 650 kA, BT(0) = 0.55 T • Substantial increase in stored energy during H-mode • Stored energy increase is accompanied by edge oscillations and small ELMs • Sustained Te(0) = 5 - 6 keV

  20. Very broad RF electron power deposition profile (Qe)in H-mode; off-axis trapping significantly reduces xD PRF = 1 MW GENRAY-ADJ GENRAY-ADJ Ip = 650 kA, BT(0) = 0.55 T Helium kf = - 8 m-1 • RF power coupled to plasma directly heats electrons, no ion heating • xCD~ 220 kA/MW in L-Mode, xCD~ 130 kA/MW in H-Mode

  21. IRFCD and IBootstrap decline as the plasma slowly transitions from L-Mode to H-Mode TORIC-TRANSP modeling for heff = 100% Times of GENRAY-ADJ analysis L-mode  H-mode PRF = 2.7 MW

  22. fNI decreases from ~ 0.5 in L-mode to ~ 0.35 in H-mode as Pe(R) broadens & RF deposition moves more off-axis TORIC-TRANSP modeling for heff = 100% • DWT ~ 25 kJ, t ~ 17 ms  heff ~ 55% For heff = 55%

  23. Non-Inductive Strategy IP [kA] HHFW Heating of NBI H-Mode Plasmas ~ 750 ~ 500 ~ 300 H-mode Time HHFW + NBI HHFW Sustain with HHFW + NBI CHI, PF, Guns

  24. Broad Te profile increase when kf = -13 m-1 HHFW heatsIp = 900 kA, BT(0) = 0.55 T, Deuterium NBI H-mode plasma BeforeHHFW Heating PRF = 1.9 MW PNBI = 2 MW DuringHHFW Heating • Identical Te and ne H-mode profiles before HHFW power onset • During HHFW heating, ne profile remains unchanged and plasma stays in H-mode

  25. TRANSP-TORIC analysis predicts heff ~ 50% for Ip = 900 kA ELM-free NBI H-mode plasma • heff obtained from We calculated byTRANSP-TORIC: WeX – from HHFW+NBI H-mode WeR – from matched NBI H-mode WeP– using e from NBI H-mode to predict Te in HHFW+NBI H-mode • heff =(WeX-WeR)/(WeP-WeR) = 0.53 ± 0.07 • If PePis the power absorbed by electrons calculated by TORIC assuming heff =100% • Electron RF absorption, PeA= heff × PeP For PRF = 1.9 MW: • 0.7 MW electrons • 0.3 MW fast-ions • fNI ~ 0.3 (IBootstrap = 180 kA, [IRFCD+INBICD] = 60 kA) k|| = -13 m-1 Time of TRANSP-TORIC, GENRAY & CQL3D analysis

  26. GENRAY ray tracing analysis predicts broad deposition, with very little RF power reaching magnetic axis GENRAY For 1 MW of Coupled RF Power Deuterium kf = - 13 m-1 Ip = 900 kA BT(0) = 0.55 T • 75% of RF power directly heats electrons • 25% of RF power accelerates NBI fast-ions off axis

  27. CQL3D Fokker-Planck code predicts significant fast-ion losses in Ip = 900 kA ELM-free HHFW+NBI H-mode • Without fast-ion loss CQL3D predicts much higher neutron production rate (Sn) than is measured • Simple-banana-loss model predicts Sn ~ 20% below measured Sn : • Assumes prompt loss of fast-ions with a gyro radius+ banana width > distance to LCFS • ~ 60% RF power to fast-ions is promptly lost • Significant prompt fast-ion loss is due toRF wave-field acceleration occurringpredominantly off-axis Time = 0.340 s

  28. HHFW+NBI H-modes can exhibit a significant RF power flow in the scrape-off layer (SOL) to the lower divertor BT(0) = 0.45 T BT(0) = 0.55 T • RF power flow produces local hot region on divertor plate that moves with changes in the magnetic field pitch • ELMs increase RF power flow to the divertor Ip = 0.8 MA PRF = 2.6 MW kf = - 8 m-1 PNBI = 2 MW J. C. Hosea, et al., Poster A33

  29. AORSA simulations of NBI+HHFW H-modes predict large amplitude coaxial modes at long launch wavelengths • Large amplitude, non-propagating coaxial modes form in SOL can dissipate significant RF power if collisionally damped AORSA full wave simulation of NBI+HHFW H-mode PRF=1.9 MW PNBI = 2 MW Ip = 1 MA BT(0) = 0.55 T 130608 @ 0.353 ms D. L. Green, et al., Poster A36

  30. Summary • Generated HHFW-only "ELM-free-like" H-modes that have rising Wtot, high Te(0), fNI up to 0.65, and sometimes ITBs • Improved antenna & plasma conditioning enabled a broad increase in Te(R) when HHFW was coupled to an ELM-free NBI-generated H-mode • A significant RF power flow along field lines in the SOL produced a hot region on the lower divertor plate that moves with change in field pitch • 3-D simulations that include the SOL predict modes in the SOL and plasma edge that appear qualitatively similar to observed RF power flow • Similar edge/SOL RF power flows may be important in ITER NBI+ICRF H-mode scenarios, these need to be modeled with advanced RF codes

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