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Effects of Lithium-Coated Plasma-Facing Components on NSTX Discharges

Robert Kaita, PPPL

For the NSTX Research Team50th Annual Meeting of the APS Division of Plasma Physics

Reunion A, Hyatt Regency Hotel, Dallas, TXNovember 17, 2008

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 2November 17, 2008

Introduction

• Lithium plasma-facing components (PFCs) have potentially attractive features for reactors, e. g., reducing recycling and mitigating effects of high heat and radiation fluxes

• Dramatic effects of lithium PFCs on plasma performance demonstrated on TFTR, T-11M, FT-U, CDX-U, TJ-II, etc.

• Recent NSTX experiments have shown significant and recurring benefits of lithium PFCs including:– Reduced plasma density early in discharge– ELM suppression and longer pulse length– Improved energy confinement– Reduced flux consumption– Broader electron temperature profile– Reduced scrapeoff layer plasma density

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 3November 17, 2008

Two LIThium EvaporatoRs (LITERs) oriented for coating NSTX divertor region with lithium

10 cm

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 4November 17, 2008

Shutter in front of LITER exit allows rapid interruption of evaporation without cooling oven

• Helium glow discharge cleaning eliminated between shots– Helium no longer trapped by lithium

Plasma 1 s

He 6.5 min

Plasma 1 s

He 6.5 min

Continuous Li Evaporation

2007 scenario for lithium deposition

2008 scenario using shutters to block Li depositionShutterclosed

6 min minimum

Li8 min

Shutterclosed

10 minminimum

Li8 min

Li8 min

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 5November 17, 2008

ELMs suppressed and discharge duration extended in plasmas with lithium PFC coatings

• Plasma density reduced early in discharge

00.51.0Time (s)100.50101510002000103Ip (MA)PNBI (MW)WMHD (kJ)Dα ( .)arb<ne> (1020m-3)<Te> ( )keVTe(0) ( )keVPrad ( )MW<Zeff>129239 ( )no Li , 129245 (260 )mg Li

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 6November 17, 2008

Increase in stored energy (WMHD) with lithium mostly through rise in electron stored energy (We)

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 7November 17, 2008

No Li

S. Kaye

No Li

TRANSP analysis indicates increase in edge current

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 7November 17, 2008

• Higher pedestal gradients raise edge boostrap current– Consistent with “second stability” and ELM suppression

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 8November 17, 2008

Lithium PFC coatings reduce OH flux consumption

• Lower average loop voltages mean more efficient flux consumption– Internal inductance decreases as electron temperature profile broadens

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 9November 17, 2008

Electron temperature profile broadening observed in discharges with lithium PFC coatings

0.51.01.5Radius (m)ne (1020m-3)0.00.51.00.51.01.5Radius (m)Te (keV)129239 (no Li), 129245 (260mg Li)t=0.62st=0.62s0.00.51.0 12939 (no Li), 12945 (260mg Li)

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 10November 17, 2008

2 lines fit in this headerso I can put too many words in my title

Scrapeoff layer profiles indicate density reduction with lithium-coated PFCs and suggests lowered recycling

• Modeling in progress with UEDGE multi-fluid transport code– Shows variation in magnitude of edge density with recycling coefficient– Presently matches density profile shape only in high Li deposition case

• Suggests need to include change in transport in simulations

129024Low Lideposition

129041High Lideposition

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 11November 17, 2008

Lithium coating from stream of lithium powder into scrapeoff layer similar to LITER in effect on plasma performance

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

~40m lithium particlesdropped from canister above

during discharge

0

1000130389

IP (kA)

129064129012

0

5

130389

PNB.. (MW)

129064129012

-2

-1

0

1

2

x104

130389

IOH (amperes)

129064129012

0

5

130389

VINEAV (E20)

129064129012

0

1

2

3

x105

130389

WMHD.. (J)

129064129012

0

1

2

3

4130389

DALPHA_CH (volts)

129064129012

0 10

1

130389

LI <LF(0.0200)> (-)

Time (s)

129064129012

0 10

1

2

3

4130389

BOLOM_TOTPWR (MW)

Time (s)

129064129012

0 10

5130389

CII.. (volts)

Time (s)

129064129012No lithium; 700mg LITER; 7 mg Powder

0 1

TIME (s) 0 1

TIME (s)

Plasma Current (kA) Neutral Beam Power (MW)

Stored Energy (J) Average Density (1019 m-3)

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 12November 17, 2008

Summary

• Recent NSTX experiments have shown improved plasma performance with lithium-coated PFCs– Obtained with lithium evaporation and lithium powder– Helium glow discharge cleaning between shots

eliminated for achieving H-mode– Plasma density reduced in early phase of discharge– ELMs suppressed– Energy confinement improved– Discharge length increased– Flux consumption reduced– Electron temperature profile broadened– Scrapeoff layer plasma density reduced

• Consistent with lowered recycling

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) November 17, 2008

• 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

Next step in NSTX is to begin investigation of liquid lithium on plasma facing components

Liquid Lithium Divertor (LLD) to be installed on lower divertor in 2009

13

NSTXNSTX 50th Annual Meeting of the APS DPP – Effects of Lithium-Coated PFCs (Kaita) 14November 17, 2008

Contributors and acknowledgments

*Work supported in part by US DOE Contracts DE-AC02-76CH03073,DE-AC04-94AL85000, DE-AC52-07NA27344, and DE-AC05-00OR22725

H. Kugel 1), J-W. Ahn 2), J. P. Allain 7), M. G. Bell 1), R. Bell 1), J. Boedo 2), C. Bush 3),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), 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

See posters NP6.00084, NP6.00085, NP6.00087, and NP6.00112 on Wednesday morning for more details