Lithium Research in NSTX
Josh Kallman(with thanks to R. Kaita)
Student Seminar
PPPL
July 29, 2010
NSTXNSTX
College W&MColorado Sch MinesColumbia UCompXGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton UPurdue USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU IllinoisU MarylandU RochesterU WashingtonU Wisconsin
Culham Sci CtrU St. Andrews
York UChubu UFukui U
Hiroshima UHyogo UKyoto U
Kyushu UKyushu Tokai U
NIFSNiigata UU Tokyo
JAEAHebrew UIoffe Inst
RRC Kurchatov InstTRINITI
KBSIKAIST
POSTECHASIPP
ENEA, FrascatiCEA, Cadarache
IPP, JülichIPP, Garching
ASCR, Czech RepU Quebec
Supported by
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
• 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
Liquid lithium samples exhibit low deuteriumrecycling until fully converted to LiD
10
221
021
10
20
Re
ten
tion
(ato
ms cm
-2)
1020 1021 1022
Ion Fluence (atoms cm-2)
2
National Spherical Torus Experiment atPrinceton Plasma Physics Laboratory
Goal is to reduce recycling in divertor region
• Poloidal field coil• Outboard divertor
• Inboard divertor
• Plasma
10 cm
• Capacity: 90 g Li
• Oven Temp: 600-680°C
• Rate: 1mg/min - 80mg/min
NSTX LIThium EvaporatoR (LITER) consists of heated reservoir inside stainless steel oven
• LITER central aiming axis to graphite divertor and gaussian angle at 1/e (dashed)
• Toroidal locations of LITER and Quartz Deposition Monitors (QDM)
Two LITERs oriented for coatingNSTX divertor region with lithium
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
Lithium edge conditions flatten and broaden electron temperature profiles
Without lithium coatings
With lithium coatings
Confinement improves with lithium edge conditions
Stored energy in electrons
Total stored energy
• 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
Liquid Lithium Divertor (LLD) installed on lower divertor
Next step is to replace section of divertor region with fully-toroidal liquid lithium surface
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
0.455 0.460 0.465 0.470 0.475
Time (seconds)
ELMs in lower divertor, 129019
0.2 0.4 0.6 0.8 1.0 1.2 1.4
Radius (m)
2
4
6
Q [
MW
/m^2
]
Heat flux, 129019
2
4
6
t = .33st = .36st = .39s
Arb
itrar
y un
its
Strike pointlocation
0.45
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
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
Extent of probearray
Probe array in bay B gap
Downward view
16
33 radially arrayed triple-probes provide edge temperature and density characterization on a continuous basis− can also be operated as swept or
SOL current probesProbes 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)
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
Triple Langmuir probe array addresses edge diagnostic needs
10 cm
2.5 cm
Leadingedge
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
Example: NAGDIS-II: pure He plasmaN. 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”
100 nm (VPS W on C) (TEM)
• Tungsten is only candidate for fusion reactors
– Tests involving long-term exposure to plasma reveals surface damage
Problematic nature of present solid materials motivates liquid wall research on NSTX
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 nE >T
• nE >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
Person
Plasma Major Radius 6.2 m Plasma Minor Radius 2.0 m Plasma Volume 840 m3
Plasma Current 15.0 MA Toroidal Field on Axis 5.3 T Fusion Power 500 MW Burn Flat Top >400 s Power Amplification >10
ITER to be next major step for addressing physics and engineering issues for MFE reactors
*Work supported in part by US DOE Contracts DE-AC02-09CH11466,DE-AC04-94AL85000, DE-AC52-07NA27344, and DE-AC05-00OR22725
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 USA2) University of California at San Diego, La Jolla, CA 92093 USA3) Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA4) University of Washington, Seattle, WA 98195 USA5) Columbia University, New York, NY 10027 USA6) Lawrence Livermore National Laboratory, Livermore, CA 94551 USA7) Purdue University, School of Nuclear Engineering, West Lafayette, IN 47907 USA8) Sandia National Laboratories, Albuquerque, NM 87185 USA 9) Los Alamos National Laboratory, Los Alamos, NM 97545 USA
Contributors and Acknowledgements*