An Initiative to Tame thePlasma Material Interface

R.J. Goldston, J.E. Menard, J.P. Allain, J.N. Brooks, J.M. Canik,R. Doerner, G.-Y. Fu, D.A. Gates, C.A. Gentile, J.H. Harris,A. Hassanein,N.N. Gorelenkov, R. Kaita, S.M. Kaye, M. Kotschenreuther, G.J. Kramer,

H.W. Kugel, R. Maingi,S.M. Mahajan, R. Majeski, C.L. Neumeyer,R.E. Nygren, M. Ono, L.W. Owen, S. Ramakrishnan, T.D. Rognlien,

D.N. Ruzic, D.D. Ryutov, S.A. Sabbagh, C.H. Skinner, V.A. Soukhanovskii,T.N. Stevenson, M.A. Ulrickson, P.M. Valanju, R.D. Woolley

Columbia, LLNL, ORNL, PPPL, Purdue, SNL, UCSD, U. Ill, U. Texas

CTF & Demo Present Much LargerPMI Challenges than ITER

• Higher heat flux, longer pulses, higher duty factor• CTF: 2x ITER’s heat flux; Demo: 4x ITER’s heat flux• CTF: 2 week pulses; Demo: 10 month pulses• CTF: 30% duty factor; Demo: 70% duty factor

• Erosion, dust production, tritium retention and component lifetimeissues are much more challenging due to CTF & Demo missions

• CTF and Demo must remove dust and tritium in real time• Demo is to show practical solutions that allow for continuous

operation for ~ 4 full-power years between PFC change outs.• ITER plans to change out divertors after ~ 0.08 full-power years

– at much lower power.

• Many solutions used on ITER are not Demo-relevant• Beryllium first wall• Water cooled ~200C plasma facing components• Intermittent dust collection and tritium clean-up

A Broad, Integrated Initiative is Requiredto Address the PMI Challenge

Need High Surface-Average & Divertor Heat Fluxes

P/S ~ 1 MW/m2 P/R ~ 50 MW/m

W/R ~ 5 MJ/m allows tests of ELM and disruption controlwithout risk of major damage.

Large % repetitive ELMs can mimic small ELMs on CTF / Demo

Loarte: 1999Fundamenski: 2004Maingi: 2007, 2008

Scaling: λ ~ 8 mm?

Tungsten Alloys must be Testedfor CTF and Demo

At high fluence and wall temperature, dust and foam are serious concernsRequire capability to monitor and remove dust during operationTesting must be at Demo conditions, including wall temperature

He-induced foamDust source

Nagoya University UCSD

He-Cooled Tungsten Divertor TargetsMust be Tested for CTF and Demo

• He-cooled first wall is also new territory.• Tore Supra provided the key operational experience on

water-cooled PFCʼs for ITER.• CTF will require equivalent experience from a

confinement experiment with He-cooled PFC technology.

9-Finger module 1-Finger module

Liquid Metal Divertor SolutionsMust be Tested for CTF and Demo

FTU, ItalyCapillary PorousSystem (CPS)Tmax ≤ 600C> 10 MW/m2 in T-11

• Successful tests of lithium in TFTR, T-11, FTU, CDX-U, NSTX• NSTX to test liquid lithium divertor

• Reduces recycling, improves confinement• E-beam test to 25 MW/m2 for 5 - 10 minutes, 50 MW/m2 for 15s.• Plasma focus test to 60 MJ/m2 off-normal load• Direct route to tritium removal, no dust, no off-normal damage?

• With 5% Li evaporative cooling, peak heat flux drops to2.5 MW/m2, Te ~ 5 eV, Zeff = 1.6 at the plasma edge

Alternate Divertor Concepts Must beTested for CTF & Demo

a)

Long Pulses and Hot Walls are Needed toStudy Tritium Retention for CTF and Demo

• Pulse length should be ~ 1000 sec, extensible if necessary• Tritium retention time in Demo (inventory/flow) ~ 104 sec• Total on-time ~ 106 sec / year provides for multiple 105 sec

tritium retention studies, ~10x H diffusion time in W @ 1000K• Trace tritium capability is highly desirable• Experiments must be done at Demo wall temperature ~ 1000K.

Tore SupraCarbon PFCs

Phase 2

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# 32299 # 32300

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Diff

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Access for Diagnostic, Heating, Current Driveand PFC Services is Critical

• Full view of all plasma-material interactions• Extensive in-situ surface analysis capabilities• Extensive PFC engineering performance measurements• A full set of advanced confinement, stability and sustainment

diagnostics for high-performance operation• A full set of advanced heating, current drive and control systems for

high-performance operation without damaging ELMs or disruptions• Necessary large access for He PFC cooling and heating

Tore Supra, FranceICRF antenna

NHTX Existence Proof Design PointProvides the Required Capabilities

NHTXNational High-power

advanced TorusExperiment

• R / a = 1m / 0.55m• BT / Ip = 2T / 3.5 MA• PNBI / PRF = 30MW / 30MW• P/S = 1.1 MW/m2

• P/R = 50 MW/m• W/R ~ 4 - 5 MJ/m• Excellent diagnostic access• Borated water/WC shield inside TF for

hands-on access.• Permanent outer TF and PF coils.• Flexibility provided by ability to

replace inner VV and PF coils byvertical lift.

• Internal RH will provide relevantexperience in a forgiving environment.

• Low A at 2T extends ST-CTF database

Pedestal νe* comparable to ITER

Full Steady State High-Heat-Flux Missionis Assured even at HH = 0.8, βN = 3

Transformer for start up and current ramp up.Can test Ip startup and rampup for ST-CTF.

HH = 1.3, βN = 5,No CD from RF

NHTX and IFMIF areSynergistic and Complementary

IFMIFNHTX• Materials exposed in IFMIF can be brought to NHTX to test

hydrogenic retention and any effects on PMI properties

• Bulk material properties and effects on joining determined inIFMIF can be accounted for in NHTX PFC designs

• NHTX + IFMIF address the two key feasibility issues for fusion.

A Major Initiative will Give the U.S. Leadershipin Taming the Plasma Material Interface

• Exciting long-pulse confinement experiments will operate inparallel with ITER in China, Europe, India, Japan and SouthKorea, but they do not reach Demo-relevant divertor heat fluxes,nor do they operate at relevant first wall temperature.

• We need to learn how to integrate a Demo-relevant plasmamaterial interface with sustained high-quality plasma operation.

• A strong program of theory & modeling, test stand development,and experiments on existing confinement facilities is needed.

• A new high-power, long-pulse, hot-walls confinement facility +IFMIF will address the two key feasibility issues for fusion.They will accelerate the effort to perform nuclear componenttesting in CTF and move on to Demo.