ITPA CC meeting, Moscow June 6-7, 2005 1

ITPA SOL& Divertor

ITPA Divertor/SOL Topical Group report (2004/6-2005/5)

Presented by N. Asakura for the Divertor/SOL topical groupJune 7, 2005, ITPA Coordinate Committee meeting, Moscow

• Review priorities & focus• Report on meeting participation• Discussion topics

ModellingSOL flow, 13C trace injection & Carbon transportFuelling summary

• IEA/ITPA Joint Experiments• Next meeting plans• Summary

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5th meeting in Instituto Supreior Tecnico, Lisbon, 8-11, Nov. 2004

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ITPA SOL& Divertor

Meeting and Contribution

• 5th ITPA TG meeting of SOL and divertor physics, Lisbon, 8-11 (3.5days), Nov. 2004Total of 33 participants: EU(10), US(10), JA(5), RF(1), CH(4), ITER IT(3)Divertor modelling and simulation, plasma flow, carbon transportThree Joint Meetings:

(1) Fuelling (with pedestal group, arranged by Ghendrih/Tsitrone)(2) Development of profile database (with pedestal group, arranged by A. Leonard)(3) Second separatrix effects on edge and core performances (all group, arranged by R.

Stambaugh)

• 20th IAEA meeting in, Portugal, Nov 1-6, 2004.Paper on Joint TG work: “ Expected energy fluxes onto ITER Plasma Components during disruption thermal quenches from multi-machine data comparisons” by A. Loarte et al.

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ITPA SOL& Divertor

Review of priorities

• High Priority:Understanding the effect of ELMs/disruptions on divertor and first wall structures,Tritium retention & the processes that determine it, Improve understanding of SOL plasma interaction with the main chamber,Better prescription of perpendicular transport coefficients and boundary conditions for input to BPX modelling.

• Medium-TermSOL transport (parallel and drift) & influence on C transport,High-Z materials - operational experience,Improve our understanding of processes that determine the core impurity level,The impact of the simultaneous use of different materials (e.g. tritium retention).

Topics and Priorities are same as before.

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ITPA SOL& Divertor

Summary of 5th meeting, Lisbon, 8-11 Nov. 2004

• Presentations and discussions were focused on Understanding the status of models and their predictive capability

Code to code comparisonsEffect of the dome in ITERDivertor (neutrals, radiation transport)

Plasma flow (experiment and modelling)Carbon transport

Recent trace 13C experiments on a number of tokamaks (C migration and T retention)

• Three Joint Meetings: (1) Fuelling situation (with pedestal group, arranged by Ghendrih/Tsitrone)(2) Development of profile database (with pedestal group, arranged by Leonard)(3) Second separatrix effects on edge and core performances (all group, arranged by Stambaugh)

• Status of TPB and IEA/ITPA multi-machine experiments were presented.

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ITPA SOL& Divertor

1. Critical issues in SOL&Divertor modelling in ITER

Modelling of ITER SOL & divertor is performed complex 2D codes.This session: identify areas where physical process or modelling assumptions in ITER are unjustified in order to provide more reliable predictions.

Description of the anomalous diffusion model should be introduced-> heat & particle fluxes asymmetry and neutral recyclingModelling of SOL flow, drifts

-> influence on in/out asymmetry, material transportExperimental evidence for processes determining ITER detached divertor condition(n-n collisions, Lyα absorption, He-D elastic collision, etc)Need to include kinetic effect corrections to parallel transport

-> Energic ions/electrons, impurity and ELMInclusion of Hydrocarbon & their radicals transport Divertor shape (V-shape, Gas conductance, Dome)Second separatrix effectsExtension of the calculation up to the first wallWall saturation and pumpingWall material (mixture material case)

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2.1 Modelling and Code-code comparison

Goal: Compare the EDGE codes for a series of cases with increasing physics processes, in order to understand the origin of differences and to validate codes. (covered in DSOL-14)

Code-code comparison work of divertor plasmas in progress with SOLPS(B2-EIRENE) vs EDGE2D-NIMBUS

Same grid, same plasma conditionsInitial results substantially differentdifference traced to different assumptions about kinetic parallel electron and ion energy flux limiters -> Having the same flux limiter choice in both codes brought the two closer together

Next steps: Density scan (better agreement in low ne),Inclusion of drifts (still unstable solution),C-impurity (in progress).

UEDGE to be added soon

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ITPA SOL& Divertor2.2 Modelling and Code-code comparison: drifts and impurity

• Effect of drifts was reported.In-out asymmetry in divertor plasma was commonly enhanced (B2 in JET, AUG, EDGE2D in JET, UEDGE in DIII-D) --- ExB, grad-B play an important role.Shift of divertor plasma peak, Dα & impurity emission profiles are consistent with measurements. Agreement is generally good for attached divertor, but large differences in detached plasma.Steady-state solution (conversion) for drift-ON case is

still difficult, in particular, at high density and in H-mode.

• Diffusion coefficient: D may be different for low- and high-Z. DIII-D modelling can reproduce spectroscopy results (D~0.4 for C6+, D~0.7 for C2+)

• Wall pumping: influence on detachment.

Density distributions

JET

DIII-D

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ITPA SOL& Divertor

2.3 Modelling and Code-code comparison: neutrals

UEDGE modelling of C-Mod divertor (Lisgo): (covered in DSOL-5)• Divertor plasma with diffusive neutrals and radiation absorption

(need high n0L to be ITER-like)• Previous attempts failed to match divertor pressure to factor of 10• New results increased divertor pressures by the factor of ~5• Several effects were found to be important (implications for ITER)

Photon transport (Ly-series absorption in detached divertor)Neutral viscosity, ion-neutral collisions

Neutral pressure in C-MOD divertor

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2.4 Role of divertor geometry

Common understanding of divertor geometry effects was summarized:Heat load reduction:

Effects of divertor geometry on target power load: vertical target is preferable.Radiation enhancement:

More closed divertor geometry enhanced radiation enhancement (AUG), but not at JET.Particle control &pumping:

Divertor geometry can be used effectively to optimise D/T and recycling impurity pumping Neutral control:

Neutral compression can be affected by divertor closure. but maximum determined by separatrix locations

Detachment : Spatial variation of plasma detachment along divertor target can be influenced by divertor

geometry. However, complete detachment and density limit are not much affected.Septum/Dome:

Effect of septum on asymmetry in plasma and detachment were seen in JET, but over very small range of separatrix-septum distances.

SOL plasma property: Effects of divertor geometry on ion &impurity flows, SOL width and impurity shielding are

very minor, besides increased pumping of recycling impurities.

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ITPA SOL& Divertor3. Parallel SOL flow (1)

• New results (drift, geometry, impurity flow) were reported in JET, TCV, C-MOD, DIII-DPower scan & Bt reversal (plasma top in JET), Impurity flow(plasma top in DIII-D),Geometry effect: upper/lower null (outer midplane in TCV)

upper/lower/double null (inner&outer midplane in C-MOD)• Investigation of driving mechanism of subsonic flow in main plasma was in progress(1) “Drifts” in simulation (EDGE2D, B2 in JET, UEDGE in JT-60U) was not enough (2-5 times

smaller) to explain subsonic flow in main SOL.(2) Poloidal asymmetry in diffusion coefficient (D~1/Bα) increases M// (EDGE2D, B2).(3) Outward pinch increases M// to subsonic level (EDGE2D).

* However, physics model is not understood. M// at separatrix does not increase.

Drift changes M// at sep. Asymmetric D changes M// at outer radius

B2 simulation in JET with drifts/variable D

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ITPA SOL& Divertor

3. Parallel SOL flow (2)

• Subsonic flow may be driven by asymmetries in perpendicular transport (C-MOD).

High radial ion flux through separatrix to Outer SOLHigh pressure outer SOLLow pressure inner SOL

Poloidal pressure asymmetry drives flow from outer to inner SOLNew measurements at inner SOL consistent with above model

Double null geometry experiment shows low ne, Te& fluctuation level. --- confirmed.

Classical drifts also play a role

Asymmetrical diffusion+drifts model will be quantified to extrapolate to ITER simulation.

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ITPA SOL& Divertor4. Carbon transport in SOL and migration (1)

Carbon deposition (location and amount) influences tritium retentionLocal deposition process were discussed in 4th ITPA meeting (Naka, 2004 Jan.).

• Transport of carbon ion in SOL has been investigated using trace gas puffs (13CD4/13CH4)Tokamak Total injection Puff location Target plasma AnalysisJET 1.3x1023C plasma top (2001) OH Analyzed

4.2x1023C outer divertor(2004) H-mode ProgressAUG 0.9x1022C outer midplane(2002-3) ELMy-H AnalyzedDIII-D 1x1022C plasma top(2003) L-mode newly analyzedTEXTOR 7x1020C limiter top (2004) L-mode newly analyzedJT-60U 3x1023C outer divertor(2004) L-mode Progress

• Qualitative evaluations of C deposition and transport were newly obtained.(1) Long-range Carbon migration: subsonic flow exists in main SOL and plays an important role.

Carbon ions are carried toward the Inner divertor and baffle (50% in JET, 30% in DIII-D). Total deposition on Inner wall (but thin layer) is also important (~40% in DIII-D).* Local deposition is also important.

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ITPA SOL& Divertor4. Carbon transport in SOL and migration (2)

Subsonic flow towards Inner divertor was confirmed experimentally and numerically:M//~0.4-0.5 (probe) is consistent with CII & CIII distribution measurements.Impact on impurity shielding (core plasma) and carbon deposition (divertor):C ion density at separatrix (CXR) is consistent with M//~0.5 case: large friction force

13C deposition pattern is consistent with M//~0.5 case: C ions deposit near strike-point

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ITPA SOL& Divertor5. Fuelling summary: Pellet injection (1)

Gas puff: particles mostly ionized in SOL -> very low fuelling efficiency (Kukushkin) Γcore =20-90Pam3s-1 (Dped=0.03-0.1) is needed to maintain ncore~1020m-3 (~ASTRA cal.)<-> Γsep< 20 Pam3s-1 and nse < 4x1019m-3 (B2-EIRENE cal.), detachment extending at higher Γsep.

Pellet:■ HFS injection is available fuelling method to obtain 20-80Pam3s-1 (for Inductive/Hybrid op.).■ HFS injection(AUG) evaluated pellet size for ELM triggering (d>0.6mm was enough)

-> ITER: d>4mm with v>0.5km/s would be enough to penetrate into MHD active region.■ Pellet injection for ELM mitigation was evaluated in ITER (Polevoi, et al.), based on JT-

60U,DIII-D, AUG HFS pellet exp.: HFS PI is better effect, but enhances nHe/ne to 2-9%. LFS PI will is better choice for SS operation with less fuelling.

■ Steady-state ne control during 2 min (155 pellets) in ToreSupra (also using LH notching)■ Wall retention was comparable to puff (T-S) due to limiter operation? -- should be confirmed.

AUG HFS pellet

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ITPA SOL& Divertor5. Fuelling summary: Supersonic Gas (2)

Supersonic Molecular Beam: getting popular ( HL-1M, HL-2A, W7-AS, AUG, ToreSupra)Whereas efficiency was reasonable so far, compatibility in ELMy H, distance to plasma, and influence on SOL/detachment should be investigated.ToreSupra: systematic study of LFS & HFS SMB (200Pam3s-1 in 2ms, Mach ~5),

Fuelling efficiency (40-60%) did not decrease with ne(3-7x1019m-3), power(LH: 0-5MW), and it was comparable between LFS and HFS.

However, influence on SOL plasma (Isat increased, Te decreased, M// changed)AUG : efficiency decreased to ~10% in 5MW NB ELMyH-mode (6x1019m-3: high ne and ELM).

ToreSupra pellet&SMB ASDEX-U SMB

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ITPA SOL& Divertor5. Fuelling summary: CT and Wall fuelling (3)

CT injection: demonstrated in TdeV(0.16MA/1.4T), JFT2M(0.15kA/1T,OH/0.5MW NB)Efficiency of ~50% (40-100%) was good, but ∆N (<1019m-3) was small due to small CT size.Dissociation time of ~100µs was required due to reconnections, etc. (tentative size experiment)Metal from electrode is another concerning.

Potential capability to control injection velocity and length, which is attractive for profile control and momentum injection in SS operation. At the same time, particle inventory (a few %) is very small compared to pellet (~50%).•Injection into NSTX (large plasma volume) is planned in 2007-8. •Design work was finished in JT-60U/JET, and ITER (20cm dia. and length, 1023m-3, <20Hz)

Wall fuelling from saturated wall: pointed out in steady-state operation (TRIAM-1M).Wall temperature control by water cooling (<100C) suppressed neutral flux from co-deposited

layers of Mo+O (D/Mo~0.35)-> Pumping dominated wall: extending the long pulse operation up to 5 hours using gas puff FB.

Change in wall pumping/fuelling with surface temperature, and SOL/divertor shielding with active divertor pumping in normal density regime (ne/nGW>0.3-0.4) should be investigated--next issue

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ITPA SOL& Divertor

Summary

•Central focus of the Lisbon meeting was modellingApparent that modelling codes have many parameters that are set differently by different ‘operators’

leading to different results.Flux limiting, Mach limit at plate, grid edge boundary conditions…

Code-code comparisons very useful. Long-term testing planned Improvements in codes being pursued as well

Handle 2nd separatrix and grid to walls, high density divertor (e.g. Lyα absorption…)•SOL flows

Subsonic SOL flow (plasma & carbon) is confirmed by probe, spectroscopy, 13C dep.Stagnation point shifted to outer (LFS) SOL, high Mach # at inner (HFS) edgeDriven by combination of perpendicular transport and poloidal drifts

(it will influence on predictions of C-deposition, T-retention, impurity concentration.)•Impurity tracer experiments reviewed

Expected results of flow to inner divertor (13C & W),13C trace experiments from outer divertor is under investigation(JET, JT-60U).

•FuelingHigh-field pellets primary choicefor for >20Pam3s-1. ELM triggering/mitigation has been progressed.SMBI(Supersonic jet) is good efficiency. Compatibility with ELM and high ne should be studied.CTs show better efficiency: but tentative CT is small size, problems of penetration and impurity.

•Proposals of IEA/ITPA experiments/study increased from 7(2004) to 15.

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ITPA SOL& Divertor

Topics for next (6th) meeting, 7th meeting plan

Topics to discuss in 6th meeting in Taragona, Spain, July 4-7, 2005 (after EPS)• D/T inventories at surface and side of tiles (updated experiences since 4th meeting)

In particular, we focus on side of tiles, which was question in 4th meeting.• Dust (Model of movement + summary of existing knowledge) : first session

Potential problem for T retention. Physics of dynamics is recently developed.• High-Z experiences (updated experiences since 4th meeting)• Fast wall loading in disruption and ELM (joint session with MHD group)• Mix-material effects on sputtering (Be in C, Be in W, C in W were question in 4th meeting)• Effect of Be operation in ITER (including data from JET and laboratory)• Dome effects (one of important questions to finalize ITER divertor design)• Progress report/new proposals of IEA/ITPA experiments• Report/discussion of TPB

7th meeting: expected in early Jan. 2006 before/after PSI paper selection meeting, potential locations – Hefei (China). Or Naka (or other location), Japan.

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ITPA SOL& Divertor

IEA/ITPA work status (1/7)

DSOL-1 Scaling of Type-1 ELM energy loss and pedestal gradients through dimensionless variables (Loarte/ Kallenbach)

Category for 2005: E ELM database is sheared with PEP-2.Keypersons: A. Loarte(JET), M. Kempenaars, G. Saibene, A. Kallenbach, L. Horton,

A.Leonard, T. Osborne, M. Fenstermacher, P. Snyder, H. Urano, G. Counsell and A. KirkProposal: JET, DIII-D (2005-6), ASDEX Upgrade , JT-60U, MAST

JET-DIII-D low ν* regime discharges with improved diagnostics. Access the role of Pin at low ν* on ELM energy losses. Comparative study of role of δ on pedestal and ELM losses.

DSOL-2 Hydrocarbon injection to quantify chemical erosion (Philipps/Roth)Category for 2005: EKeypersons: V. Philipps (FZJ Juelich) S. Brezinsek (FZJ Juelich), M.Stamp (JET), R. Pugno

(AUG), T.Nakano (JT-60U), M.Fenstermacher (DIII-D)Proposal: TEXTOR, JET, AUG, DIII-D, JT-60U

New experiments ate planned in TEXTOR(C2Dx, C3H4 injection in detachment plasma), DIII-D(CH4+He injection in detached and attached divertors),AUG (flux dependence from 1021-1022 m-2s-1 in attached divertor), JET(CD4, CH4, C2H4 injection), JT-60U(CD4, CH4, C2H4, C2H6 in attached and detached divertor

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ITPA SOL& Divertor

IEA/ITPA work status (2/7)

DSOL-3 Scaling of radial transport (Lipschultz)Category for 2005: EKeypersons: B. Lipschultz(C-mod), G. Matthews(JET), T. Leonard(DIII-D), S. Lisgo(C-mod), A.

Kallenbach(AUG), R. Pitts(TCV)Proposal: C-mod, JET, DIII-D, MAST (added in 2005), AUG (added in 2005)Investigate turbulence and time-averaged plasma data in extending devices(MAST, AUG, TCV)

DSOL-4 Disruption energy balance in similar discharges in the ITER QDT = 10 scenario(A. Loarte, D. Humphreys, G.Pautasso)

Category for 2005: EKeypersons: A. Loarte, P. Andrew, V. Riccardo, A. Kellman, D. Humphreys, G.Pautasso, G. Counsell,

D. Whyte, K. Tsuzuki,A. HerrmannProposal: JET, DIII-D, ASDEX Upgrade, MAST, JT-60U

JET-DIII-D and others: plasma parameters extending to (1) ITER like δ~0.5, q95=3 and Type-I ELM regime, (2) impurity puff, (3) during growing NTM condition.

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ITPA SOL& Divertor

IEA/ITPA work status (3/7)

DSOL-5 Role of Lyman absorption in the divertor (Reiter)Category for 2005: EKeypersons: D Reiter, J Terry, G Matthews, S LisgoProposal: C-Mod (data provided and being modelled), JET (planning for data)･ Self-consistent B2-EIRENE ITER modelling with photons,･ Comparison with Lyβ:Baα C-Mod observations of photon trapping･ Plasma/photon modelling of higher density C-Mod plasmas･ Measurement of Lyβ:Baα ratios on JET, divertor modelling･ Zeeman and non-Maxwellian neutral velocity effects

DSOL-6 Parallel transport in SOL (N. Asakura)Category for 2005: Closed in 2005Keypersons: N Asakura, G Porter, B LaBombard, K Erents(Proposal: DIII-D, JET, JT-60U, TCV, ASDEX-U, MAST)

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ITPA SOL& Divertor

IEA/ITPA work status (4/7)

DSOL-7 Study on separatrix density and edge density profiles (Kallenbach)Category for 2005: PKeypersons: A. Kallenbach (AUG), G. Porter (DIII-D), A. Hubbard (C-Mod), N. Asakura (JT60-U), A.

Kirk (MAST), W. Suttrop, L. Horton, T. Osborne, D. Coster , W. Fundamenski(JET)Proposal: Data from C-Mod, ASDEX-Upgrade and JET analyzed, other experiment results being added.

AUG divertor data and B2/Eirene modelling displayed with cview by G. Conway which is routinely used to plot AUG and JET data plus additional machine and code data supplied in appropriate MDSplus format. Experimental data in divertor tree nodes are processed raw data: calibrated, optional: profiles from strike point sweeps, coherent ELM averaging etc.

DSOL-8 Radial transport of ELM: move to PEP-10DSOL-9 C-13 injection experiments to understand C migration(Philipps)Category for 2005: EKeypersons: Guy Matthews(JET) , P. Stangeby (DIII-D), V. Philipps (Textor), K. Tsuzuk(JT-60U), V. Rohde, C. Skinner

Proposal: JET, DIII-D, TEXTOR, ASDEX-Upgrade, JT-60U, NSTXFast SOL flow is a major aspect of the process. Most SOL flow data is from Mach probes, which have significant interpretation issues and, in any case, don’t measure the carbon ion flow, which may differ from the fuel ion flow. 13C experiments can tell us directly where the carbon itself goes.

13C experiments can be useful for carrying out quantitative oxidation experiments (tritium recovery) aimed at establishing the ability to recover T from different types of co-deposit at different locations.

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ITPA SOL& Divertor

IEA/ITPA work status (5/7)

DSOL-10 Modeling of different gases effects on the power deposition (Whyte)Category for 2005: PKeypersons: D. Whyte (UW-Madison), M. Bakhtiari (JT-60U), K. Tsuzuki, Y. Kawano(JT-60U),P. Andrew (JET), Martin (TS), E. Tsitrone(TS),Matthews (JET), Hollmann (DIII-D)Proposal: DIII-D, JET, C-ModRunaway suppression is possible with many gases, but optimal dissipation of ITER thermal energy on longer timescale to avoid melting appears difficult.

DSOL-11 Disruption mitigation experiments (Whyte)Category for 2005: E, recommended to combine MDC-1Keypersons: D. Whyte (UW-Madison), T. Jernigan (ORNL), E. Hollmann (UCSD), M. Bakhtiari (JT60-U),K. Tsuzuki, Y. Kawano(JT-60U), G. Martin (Tore Supra), F. St-Laurent(TS),V. Riccardo (JET), P. Andrew (JET), R. Granetz (MIT), J. Terry (MIT), K. Erents (JET), G. Matthews (JET), K.H. Finken (Juelich), G. Pautasso(AUG)Proposal: DIII-D, JT-60U, Tore Supra, JET, Alcator C-Mod,TEXTOR, AUGCross-machine comparisons of gas jet designs and target plasmas continue, now including JET and C-

Mod, in order to provide better empirical extrapolation to ITER.

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IEA/ITPA work status: Starting proposals (6/7)

DSOL-12 Oxygen wall cleaning (Stangeby)Category for 2005: EKeypersons: P.Stangeby (U of Toronto/GA/LLNL), V. Philipps (Textor), J. Li (Hefei, HT-7), J. Roth (AUG)Proposal: TEXTOR, HT-7, DIII-D, AUG

Procedure of combination experiences with 13CH4 injection and Oxygen baking is proposed in DIII-D by Stangeby. Quantitative understanding of C and O removal will be explored.

TEXTOR reported an oxygen bake experiment in 1999 and is planning further such experiments for the near future. Procedure of combination experiences with 13CH4 injection and Oxygen baking is proposed in DIII-D by Stangeby. Quantitative understanding of C and O removal will be explored.

DSOL-13 Deuterium codeposition with carbon in gaps of plasma facing components (Krieger)Category for 2005: PKeypersons: K. Krieger (ASDEX-Upgrade), A. Litnovsky (Textor), C. Wong (DIII-D), B. Lipschultz (C-Mod), E. Tsitrone(TS), K. Masaki(JT-60U)Proposal: data from AUG, TEXTOR, DIII-D, C-mod, Tore-Supra, JT-60UAUG: 2x2 monoblock probe with variable gap width for exposure at divertor/OSPTEXTOR: New monoblock matrix with variable gap widthDIII-D: Gap probe exposures with different plasma conditions.

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IEA/ITPA work status: New proposals (7/7)

DSOL-14 Benchmarking of Edge Simulation Codes Topical Group (Coster)Category for 2005: PKeypersons: David Coster(JET/AUG), Xavier Bonnin, (Aki Hatayama), (Hisato Kawashima), Tom Rognlien, Jim Strachan, R. Pitts (TCV)Proposal: Codes only, AUG, JET so far

Code-code comparison work of divertor plasmas in progress with SOLPS(B2-EIRENE) vs EDGE2D-NIMBUS, vs UEDGE.(1)Density scan (better agreement in low ne), (2) Inclusion of drifts (still unstable solution), (3) C-impurity (in progress).

DSOL-15 Inter-machine comparison of blob characteristics (Terry)Category for 2005: EKeypersons: J. Terry (C-Mod), S. Zweben (NSTX), C. Hidalgo (TJ-II), R. Maqueda (NSTX), O. GrulkeProposal: C-Mod, NSTX, TJ-IICoordinated fast camera images acquisition across tokamaks. Comparison of blob characteristics

DSOL-16 ICRH Wall conditioning for hydrogen removal (Ashikawa)Category for 2005: proposal was not listed in IEA/ITPA table: negotiation not completed until Nov. 2004.Proposal: LHD, Tore Supra, HT-7Working gas; He, He 2nd harmonics will be used. Campaign (- Jan, 2005), After long pulse operations, ICRF conditioning is also effective ( to remove remained H2 in the wall), Gas pressure scanning.