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Lithium Research in NSTX

Investigating advantageous properties of liquid lithium in NSTX experimental plasma, aiming to reduce recycling in the divertor region by coating with lithium and studying its effects.

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Lithium Research in NSTX

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  1. NSTX Supported by Lithium Research in NSTX College W&M Colorado Sch Mines Columbia U CompX General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI 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 Josh Kallman (with thanks to R. Kaita) 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 KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec Student Seminar PPPL July 29, 2010

  2. Advantageous properties of lithium demonstrated in PISCES-B steady-state plasma experiments at UCSD Ion flux (m-2 s-1) 1023 Ion energy (eV) 20-300 Heat flux (MW/m2) 1-10 Te (eV) 2-40 ne (m-3) 1017-1019 Pulse length steady-state Target materials C, W, Be, Li, etc. and coatings Plasma species H, D, He

  3. Liquid lithium samples exhibit low deuteriumrecycling until fully converted to LiD • Ion flux determined from double Langmuir probe measurements of plasma parameters • Cross-checked against total current to sample • Deuterium retention measured after removing sample from PISCES-B and baking in vacuum furnace equipped with residual gas analyzer (i. e., Thermal Desorption Spectroscopy) • Post-exposure outgassing of liquid lithium samples shows 100% retention of all incident deuterium plasma ions • Retention is independent of sample temperature during exposure • High recycling resumes once sample is fully converted to LiD 1022 1021 1020 Retention (atoms cm-2) 1020 1021 1022 Ion Fluence (atoms cm-2)

  4. National Spherical Torus Experiment at Princeton Plasma Physics Laboratory 2

  5. Goal is to reduce recycling in divertor region • Plasma • Inboard divertor • Outboard divertor • Poloidal field coil

  6. NSTX LIThium EvaporatoR (LITER) consists of heated reservoir inside stainless steel oven 10 cm • • Capacity: 90 g Li • • Oven Temp: 600-680°C • • Rate: 1mg/min - 80mg/min

  7. Two LITERs oriented for coatingNSTX divertor region with lithium • LITER central aiming axis to graphite divertor and gaussian angle at 1/e (dashed) • Toroidal locations of LITER and Quartz Deposition Monitors (QDM)

  8. Multipulse Thomson Scattering is primary electron temperature and density diagnostic • Doppler broadening gives temperature • Intensity of scattered light provides density • Backscattering geometry permits high sensitivity and spatial resolution at outer edge, and nearly full radial profile • 1 cm edge resolution, 3 - 5 cm at center, 8 - 10 cm on inner edge • 2 Nd:YAG 30 Hz lasers

  9. Lithium edge conditions flatten and broaden electron temperature profiles With lithium coatings Without lithium coatings

  10. Confinement improves with lithium edge conditions Stored energy in electrons Total stored energy

  11. Next step is to replace section of divertor region with fully-toroidal liquid lithium surface Liquid Lithium Divertor (LLD) installed on lower divertor • Lithium in porous molybdenum surface to be kept liquid by heated copper substrate • Objective is to determine if liquid lithium can sustain deuterium pumping beyond capability of solid lithium coatings

  12. Physics requirements for a Langmuir probe array to measure divertor profiles • Heat flux profile at outer strike point has FWHM of 10 cm • current IR camera resolution is 16 data points over this region • higher spatial resolution could allow more accurate particle flux measurements • ELMs occur on a time scale of several ms • temporal resolution should be sufficient to operate during transient events (single tip probes would be limited by voltage sweep rate) • triple probes would provide instantaneous data Heat flux, 129019 Strike point location t = .33s t = .36s t = .39s 6 Q [MW/m^2] 4 2 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Radius (m) ELMs in lower divertor, 129019 6 4 Arbitrary units 2 0.45 0.455 0.460 0.465 0.470 0.475 Time (seconds)

  13. Highly lithiated divertor conditions present materials challenge • Elemental lithium is conductive, providing a possible path for shorting electrodes to each other or ground • Lithium also reacts with carbon in the presence of oxygen (residually present in NSTX vacua) to form lithium carbonate, an insulator • this effect is beneficial in avoiding grounding and direct conduction, but can provide barrier for incident electrons and ions • previously installed Langmuir probes show no appreciable loss of signal with heavy lithium loading, but NSTX could deposit amounts an order of magnitude greater than previous years to fill LLD • Strike point ablation can remove evaporated lithium, but large integral effect of continuous loading depositions is unknown • alternate cleaning methods, such as high current pulses to electrodes, are under investigation

  14. Probe array is located near LLD to provide local measurements • Probe array begins just outboard of CHI gap and extends over roughly 1/3 of LLD radially • Provides local measurements for plasma incident on both carbon and lithium PFCs • As seen in next slide, edges of tile had to be sloped to accommodate height of as-built LLD without changing probe dimensions LLD Probe array in bay B gap Extent of probe array Downward view

  15. Triple Langmuir probe array addresses edge diagnostic needs Leading edge • 33 radially arrayed triple-probes provide edge temperature and density characterization on a continuous basis • can also be operated as swept or SOL current probes • Probes based on MAST design involving a macor cassette of closely spaced probes embedded in a carbon tile • tile mount with radial coverage of divertor (Bay B) • electronics provided by UIUC (see adjacent poster by M. Jaworski) 2.5 cm 10 cm • Close spacing of probes provides better resolution in high-gradient (strike point) regions • each probe covers 3 mm radially, including spacing • probe heads are 2mm radial x 7mm toroidal rectangles

  16. Liquid Metals Provide Possible Solution for “First Wall” Problem in Fusion Reactors • Liquid metals can simultaneously provide: • Elimination of erosion concerns • Wall is continuously renewed • Absence of neutron damage • Substantial reduction in activated waste • Compatibility with high heat loads • Potential for handling power densities exceeding 25 MW/m2

  17. Problematic nature of present solid materials motivates liquid wall research on NSTX 100 nm (VPS W on C) (TEM) • Tungsten is only candidate for fusion reactors • Tests involving long-term exposure to plasma reveals surface damage Example: NAGDIS-II: pure He plasma N. Ohno et al., in IAEA-TM, Vienna, 2006 • Bombardment with 3.5x1027 He+/m2 at Eion = 11 eV for t = 36,000 s • Structures appear on scale of tens of nm and reflect swelling due to “nanobubbles”

  18. Future research beyond NSTX to focuses on requirements for “burning” D-T plasmas • Power Balance: PH+P=PL • PL proportional to nT/E and P proportional to n2 • PH =0 or “ignition” means n2 > nT/E or nE >T • nE >1.5x1020m-3s for T=30keV • Power amplification factor Q=5P/PH • Q -> infinity as PH ->0 • New ITER device designed to achieve Q>10

  19. ITER to be next major step for addressing physics and engineering issues for MFE reactors Person

  20. Contributors and Acknowledgements* H. Kugel 1), J-W. Ahn 2), J. P. Allain 7), M. Baldwin 2), M. G. Bell 1), R. Bell 1), J. Boedo 2), C. Bush 3), R. Doerner 2), R. Ellis 1), D. Gates 1), S. Gerhardt 1) T. Gray 1), J. Kallman 1), S. Kaye 1), B. LeBlanc 1), R. Maingi 3), R, Majeski 1), D. Mansfield 1), J. Menard 1), D. Mueller 1), C. Neumeyer 1), M. Ono 1), S. Paul 1), R. Raman 4), A. L. Roquemore 1), P. W. Ross 1), S. Sabbagh 5), H. Schneider 1), C. H. Skinner 1), V. Soukhanovskii 6), T. Stevenson 1), D. Stotler 1), J. Timberlake 1), W. R. Wampler 8), J. Wang 9), J. Wilgen 3), and L. Zakharov 1) 1) Princeton Plasma Physics Laboratory, Princeton, NJ 08543 USA 2) University of California at San Diego, La Jolla, CA 92093 USA 3) Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA 4) University of Washington, Seattle, WA 98195 USA 5) Columbia University, New York, NY 10027 USA 6) Lawrence Livermore National Laboratory, Livermore, CA 94551 USA 7) Purdue University, School of Nuclear Engineering, West Lafayette, IN 47907 USA 8) Sandia National Laboratories, Albuquerque, NM 87185 USA 9) Los Alamos National Laboratory, Los Alamos, NM 97545 USA *Work supported in part by US DOE Contracts DE-AC02-09CH11466, DE-AC04-94AL85000, DE-AC52-07NA27344, and DE-AC05-00OR22725

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