Discussion of PFC/particle/lithium plans for NSTX-U

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NSTX-U. Supported by . Discussion of PFC/particle/lithium plans for NSTX-U. J. Menard for the NSTX Research Team. 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
NSTX-U Supported by Discussion of PFC/particle/lithium plans for NSTX-U J. Menard for the NSTX Research Team 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 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 NSTX Physics Meeting PPPL – B318 Monday, January 30, 2012 Overview
  • This presentation is meant to provide strawman plans and ideas, and motivate discussion
  • It is up to TSG groups and the NSTX-U team to modify, improve, formulate the PMI plan Common questions:
  • How will NSTX-U control particle inventory (main ion, impurities) for long pulse lengths?
  • How will NSTX-U handle very high heat fluxes at high current and heating power?
  • How will NSTX-U research contribute to the development of PMI solutions for FNSF/Demo?
  • Scenarios exist which trend toward stationary D and C inventory – but how do they extrapolate?
  • Li coatings + triggered ELMs come closest to achieving stationary D inventory and Zeff
  • How do these results project to NSTX-U parameters?
  • Up to 5x longer pulse
  • Up to 2x higher NBI fueling
  • How persistent is D pumping by Li?
  • Can we use run days where large lithium evaporation was only performed in morning, or at beginning of week, to inform the pumping persistence question?
  • This issue will begin to be addressed in FY2012 BP+LR research milestone
  • J. Canik - PRL 104, 045001 (2010) NSTX-U scenarios with high current and power are projected to challenge passive cooling limits of graphite divertor PFCs
  • High IP scenarios projected to have narrow lqmid ~3mm
  • At high power, peak heat flux ≥ 9MW/m2 even with high flux expansion ~60 with U/L snowflake
  • Numbers shown ignore radiation, plate tilt, strike-point sweeping
  • 0 mg Li: a=1.6 150 mg Li: a=1.1 300 mg Li: a=0.4 λqmid ~ Ip-a
  • Passive cooling ok for low-IP scenarios
  • Long-pulse + high IP andpower may ultimately require active divertorcooling
  • Major goal of NSTX-U PMI research will be investigating high flux expansion snowflake + detachment for large heat-flux reduction
  • UEDGE modeling performed comparing conventional divertor to snowflake
  • V. Soukhanovskii (LLNL) – EPS 2011
  • Snowflake synergistic with detachment/radiativedivertor
  • 5-10x peak heat flux reduction
  • What are predictions for NSTX-U regimes? And for FNSF/Demo?
  • Is this configuration compatible with cryo-pumping and/or lithium pumping?
  • NSTX-U aims to address a wide range of PFC/PMI issues flux expansion snowflake + detachment (baseline/initial NSTX-U, long-range goal)
  • D pumping method
  • Li coatings
  • Cryo-pumping, flowing liquid lithium
  • Recycling, fueling techniques
  • High recycling (RP~0.98), edge fueling
  • Intermediate/low recycling (RP~0.90-0.98/0.5-0.9), core fueling
  • Heat flux mitigation methods
  • High flux expansion, partial detachment/radiativedivertor
  • Flowing liquid metal, CPS/evaporative cooling, lithium radiation
  • Plasma facing component material
  • Graphite
  • Molybdenum, tungsten
  • PFC cooling and heating
  • Passive cooling of divertor PFCs, room-temperature first-wall
  • Active cooling/heating of divertor/first-wall (long-pulse ops/retention & diffusion)
  • Lithium coatings will continue to flux expansion snowflake + detachment be an important research tool for NSTX-U R. Maingi, et al., PRL 107, 145004 (2011)
  • Work with LTX to understand Li chemistry, impact of wall temperature, Li coating thickness
  • Assess D pumping vs. surface conditions (MAPP), lab-based surface studies, PFC spectroscopy
  • Design/develop methods to increase Li coating coverage:
  • upward evaporation
  • evap into neutral gas
  • Li paint sprayer
  • Assess impact of full wall coverage on pumping, confinement
  • Test Li coatings for pumping longer tpulse NSTX-U plasmas
  • Energy confinement increases continuously with increased Li evaporation in NSTX
  • High confinement very important for FNSF and other next-steps
  • what is tE upper bound?
  • Divertor flux expansion snowflake + detachment cryo-pumping being analyzed for D particle control
  • The persistence of Li coatings for D pumping presently not well characterized
  • Unknown if Li coating will pump 5s NSTX-U
  • May be possible to extrapolate to NSTX-U using time-depdendent SOLPS analysis of NSTX discharges with Li coatings
  • Cryo-pumping and Li-coating RP evolution to be addressed in FY12 BP milestone
  • Cryo-pumping is being assessed for compatibility with NSTX-U geometry, in-vessel components, and boundary shapes desired for NSTX Upgrade operations
  • Attempting to identify designs that do not modify passive plates or supports
  • Assume divertor region will be modified
  • Length of baffle, details of pump entrance will be critical parameters to optimize
  • Baffle radial width J. Canik(ORNL), D. Stotler Divertor flux expansion snowflake + detachment designs should aim to be compatible with boundary shapes most likely to be utilized in NSTX-U Snowflake divertors Standard divertors
  • What is optimal radius for entrance to cryo-pump?
  • Estimate: Rent = 0.7 to 0.85m
  • Being assessed with SOLPS
  • LLD on OBD could have large surface area for particle & power exhaust
  • Potentially less sensitive to strike-point radius
  • Flowing LLD development should be studied as alternative means of particle and power exhaust, access to low recycling
  • LLD, LTX  liquid Li required to achieve pumping persistence
  • Flowing Li required to remove by-products of reactions with background gases
  • Substantial R&D needed for flowing Li
  • Need to identify optimal choice of concept for pumping, power handling:
  • Slow-flowing thin film (FLiLi)
  • Capillary porous system (CPS)
  • Lithium infused trenches (LiMIT) All systems above require active cooling to mitigate highest heat fluxes of NSTX-U
  • Elimination of C from divertor needed for “clean” test of LLD D pumping
  • May need to remove all C PFCs?
  • Possible approach:
  • Dedicate 1-2 toroidal sectors (30-60˚ each) to LLD testing
  • (and/or integrate with RDM?)
  • Test several concepts simultaneously
  • Full toroidal coverage after best concept is identified
  • C Mo Flowing LLD Direct comparison of particle control from means of particle and power exhaust, access to low recyclingcryo-pumping and flowing LLD would greatly aid development of FNSF divertor Cryo-pump
  • Could dedicate upper divertor to cryo-pumping and lower divertor to flowing Li
  • IF this is the preferred long-term approach, it argues for converting lower divertor to Mo tiles first to avoid re-doing upper divertor PFCs for cryo.
  • If flowing LLD region is sufficiently narrow radially, it could (maybe) be combined with cryo-pumping in the same divertor:
  • Utilize cryo for D pumping?
  • Utilize flowing Li + evaporative and/or radiative cooling for power exhaust?
  • Can Li pump D while taking power exhaust?
  • C BN Mo Flowing LLD Cryo-pump Flowing LLD Fueling means of particle and power exhaust, access to low recycling
  • Existing/baseline systems
  • LFS gas puffing, high-field-side (will have faster turn-off in Upgrade)
  • Supersonic Gas Injection (SGI) – 2-3x higher efficiency than LFS fueling
  • Not yet integrated into PCS control
  • NBI for core fueling
  • Cannot decouple from heating
  • Fueling will double at high power
  • 5 year plan goals
  • Need to demonstrate particle pumping (any flavor), density stationarity
  • Need real-time density signal, algorithm, and actuator(s)
  • Longer term possibilities, especially for low recycling regimes
  • Molecular cluster
  • Pellet fueling
  • CT injection
  • Plasma jets
  • Should these be part of upcoming 5 year plan?
  • Possible progression of PFC materials in NSTX-U means of particle and power exhaust, access to low recycling Baseline NSTX-U PFCs are all C (and BN) to minimize risk and cost
  • C is widely accepted to be unviable for FNSF/Demo applications due to erosion and re-deposition, retention, and neutron damage issues
  • W is viewed as most viable fusion material
  • Mo (TZM) has similar thermal/PMI properties to W, but is easier to fabricate and machine
  • One scientific limitation of the above baseline approach is that tests of high-Z PFCs – by themselves, and with lithium – are deferred/delayed
  • C BN Possible progression of PFC materials in NSTX-U means of particle and power exhaust, access to low recycling Upper Mo divertor to test Mo as PFC, Li on all Mo - requires upward Li evaporator and upper divertor diagnostics
  • Having at least one divertor be all Mo (with Li coating capability) would:
  • Enable comparisons of Mo vs. C
  • Continue research planned for 2011-12, i.e. test effects of Li on Mo PFCs w.r.t. impurity production, possible temperature clamping
  • Inform/accelerate decisions for metal PFCs
  • Baseline C BN Upper Mo divertor Mo Lower C divertor enables comparison to NSTX results, reduces risk of high-Z PFCs for initial physics/long-pulse ops goals Possible progression of PFC materials in NSTX-U means of particle and power exhaust, access to low recycling
  • Upper and lower Mo divertor enables double-null ops on similar high-Z PFCs for comparison to all C and/or upper-only Mo divertor
  • Baseline Upper Mo Upper Mo C BN Upper Mo divertor All Mo divertor Mo If upper Mo divertor performed well, could then implement lower divertor Mo tiles Possible progression of PFC materials in NSTX-U means of particle and power exhaust, access to low recycling Baseline Upper Mo Upper Mo If C plasma impurities are present at unacceptable levels, all metal tiles and/or tile coatings may be needed for the CS and/or passive plates C BN Upper Mo divertor All Mo divertor All Mo tiles Mo Lower Mo Possible progression of PFC materials in NSTX-U means of particle and power exhaust, access to low recycling NSTX-U should ultimately progress to (nearly) complete wall coverage with metallic PFCs Many possible progressions exist! Baseline C BN Mo PFCs plus W divertor Upper Mo divertor All Mo divertor All Mo tiles All Mo PFCs Mo W All metal PFCs (especially W in divertor) are most representative of what will be used in FNSF/Demo Beginning of 5 yr plan End of 5 yr plan Active PFC cooling and heating means of particle and power exhaust, access to low recycling
  • Active divertor cooling – if needed – would likely be implemented near end of 5 year plan period
  • Very little discussion of this so far…
  • PFC (first-wall) heating could be useful for:
  • Study retention/diffusion of hydrogenic species (needs high Twall)
  • Liquid Li films over large surface areas (after changing to Mo/W PFCs)
  • Consider using bake-out systems for accessing 200-350˚C
  • Possible to go to higher temperature for FNSF/Demo relevance?
  • Unclear if this can be implemented during upcoming 5 year plan – maybe implement in subsequent 5 year plan
  • Summary means of particle and power exhaust, access to low recycling
  • Urge TSG/team discussion of these issues, as they will impact NSTX-U operation, operating space, other upgrade ideas
  • What is missing or should be modified/deleted?
  • Have not yet addressed other lab-based R&D studies and proposals (such as FES materials solicitation) that could influence the NSTX-U plans and decisions
  • Such studies/proposals should be incorporated into the overall plans and work-scope for 5 year planning purposes.
  • Surface studies– collaboration with FOM/DIFFER
  • B. Koel laboratory work on Li chemistry
  • NSTX-U researcher collaborations on other fusion facilities…
  • Other?
  • Once the proposed PMI plan is decided, can assess cost and schedule estimates, assign dates to the various elements
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