Annual report 2005: ITPA Topic Group on SOL and Divertor Physics N. Asakura, B. Lipschultz and the SOL/Divertor ITPA group (4 June 2005) I. SOL and divertor physics scope: (added some topics) The physics covered by this topical group is a wide range of issues as we described in 2004 semi-annual report. Starting at the first wall and divertor, the issues include plasma-material interactions and their dependence on materials (carbon, low- and high-Z metals), hydrogen isotope recycling and their storage. A more engineering-like issue is the first-wall geometry and material, and how they affect operation, including tritium removal. Moving into the divertor and SOL plasmas, the issues become more of transport (parallel and perpendicular to the magnetic field) of hydrogenic and impurity species. At the SOL/edge interface, this group addresses the relationship of edge confinement (e.g. H-modes and density limits) and SOL/divertor plasma, physics database for ITER about transient heat and particle exhaust during ELMs and disruptions, fuelling/pumping in steady-state operation. II. SOL and divertor physics tasks:(no change) Tasks covered by this topical group is the same as we described in 2004 semi-annual report. The group should: 1) participate in developing and validating a physics concept for the divertor of Burning

Plasma Experiments on the basis of experimental, theoretical, and modeling results, 2) assist the IT in developing the divertor and boundary Physics Basis for Burning Plasma

Experiments, 3) define the goals and requirements for the ITER physics R and D program for divertor

modelling, the structure of the experimental divertor plasma database, and the program to validate the divertor models to increase their reliability as a design tool for the divertor of Burning Plasma Experiments,

4) encourage the development and analysis of edge plasma parameters from divertor experiments,

5) encourage development of divertor modeling codes, validation of the codes by analysis of experimental data from divertor tokamaks (e.g. from the edge profile database), and collection of the results of the modelling studies in a database,

6) review the progress of the IEA/ITPA joint experiments and encouraging the development of further proposals through the TG meetings.

III. SOL and divertor priority research areas:(no change) Our study priority is the same as we described in 2004 annual report.

• High Priority Research Areas ♦ 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 modeling • Medium-Term

♦ SOL transport (parallel and drift) ♦ 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)

Possible Items for Joint Work with other TGs (last topics added)

Disruption physics, heat load on the plate (shielding) and mitigation. ELMs & understanding pedestal gradient (edge-SOL profile database) Design divertor diagnostics (measurement and FB control) for BPX experiments Helium exhaust or transport in ITB plasma Density limits Fuelling techniques and performance, influence on edge plasma and wall conditions

IV. Status and proposals for ITPA/IEA work:

According to suggestions from ITPA/IEA committee members, (i) to separate a group of topics to different proposals, and (ii) to combine with similar PEP proposals. Reports from DSOL-1 to DSOL-13 in 2004, and new proposals from DSOL-14 to DSOL-16 were presented in the 5th ITPA meeting in Losbon, Nov. 2004. Report and proposals will be summarized in Appendix A. DSOL-1: Scaling of type I ELM energy loss (Loarte/Leonard)

Goal: better predict divertor and first-wall heat loadings during ELMs Areas of concentration: Determination of ELM divertor heat pulse shape, timing and amount, and appropriate model to extrapolate to ITER operation regime. Experimental involvement: JET. DIII-D, JT-60U, ASDEX-Upgrade Collaborators: A. Loarte, T. Leonard, N.Oyama, Kallenbach Category for 2004: P Report (2004): AUG(√), DIII-D(√), JET(√), JT-60U(√) 2005 proposal: New title: Disruption energy balance in similar discharges in the ITER QDT = 10

scenario(A. Loarte, D. Humphreys, G.Pautasso) Experimental involvement: JET, DIII-D, ASDEX Upgrade, MAST, JT-60U Keypersons: A. Loarte, P. Andrew, V. Riccardo, A. Kellman, D. Humphreys, G.Pautasso, G.

Counsell, D. Whyte, K. Tsuzuki,A. Herrmann Category for 2005: E

DSOL-2: Hydrocarbon injection to quantify chemical erosion (Philipps/Roth) Goal: better determine chemical sputtering yield in tokamaks

Areas of concentration Predict the parameter dependence of chemical yield in ITER carbon divertor

Experimental involvement: AUG, JET, TEXTOR, JT-60U, DIII-D Collaborators: V. Phillips, D. Whyte, G. Federici, P. Coad, P. Ghendrih, R. Neu, V. Rohde,

B. Lipschultz, J. Davis, S. Higashijima Category for 2004: P/(E)

Report(2004): AUG(√), JET(√), TEXTOR (√), DIII-D(√), JT-60U(√) 2005 proposal: Experimental involvement: TEXTOR, JET, AUG, DIII-D, JT-60U Key-persons: V. Philipps (FZJ Juelich) S. Brezinsek (FZJ Juelich), M.Stamp (JET), R.

Pugno (AUG), T.Nakano (JT-60U), M.Fenstermacher (DIII-D) Category for 2005: E

DSOL-3: Scaling of radial transport (Lipschultz) Goal: better predict divertor & first-wall power/particle loadings Areas of concentration Develop same measurements techniques for SOL profiles of ne, Te, SIon

Collection of dimensionlessly similar and dissimilar discharges for analysis Experimental involvement: C-MOD, DIIID, JET, JT-60U, MAST, NSTX Collaborators: B. Lipschultz, D. Whyte, G. Matthews, R. Pitts, G. Counsell, A. Kallenbach Category for 2004: (E) Report(2004): C-MOD (√), DIIID (√ & planned), JET (√) 2005 proposal Experimental involvement: C-mod, JET, DIII-D, MAST, AUG Keypersons: B.Lipschultz (C-mod), G.Matthews (JET), T.Leonard (DIII-D), S. Lisgo

(MAST), A. Kallenbach (AUG), R. Pitts (TCV) Category for 2005: E

DSOL-4: Disruption energy balance in similar discharges (Matthews to Loarte) Goals: Better characterize divertor/first-wall heat loading Understand if there are any size effects on the division of power loadings Evaluate the performance of different materials for divertor/first-wall Areas of concentration: Comparison of heat deposition time and profile, radiation during thermal quench in

multi-machines (over various disruptions: beta-limit, high-density, Locked-mode, etc.). Experimental involvement: AUG, DIII-D, JET, MAST, TEXTOR, TCV, C-Mod Collaborators: D. Whyte, G. Federici, G. Matthews, R. Pitts, A. Mahdavi, A. Herrmann, R.

Granetz, G.Counsell, V. Riccardo, K.H. Finken Category for 2004: P Report(2004): AUG (√), DIII-D(√), JET√), MAST (√), TEXTOR (√), FTU(√)

2005 proposal Experimental involvement: JET, DIII-D, ASDEX Upgrade, MAST, JT-60U Keypersons: A. Loarte, P. Andrew, V. Riccardo, A. Kellman, D. Humphreys, G.Pautasso,

G. Counsell, D. Whyte, K. Tsuzuki,A. Herrmann Category for 2005: E DSOL-5: Role of Lyman absorption in the divertor (Reiter) Goals: Understand whether Lyman absorption is important to include in fluid models Areas of concentration: Develop EIRENE to handle radiation transport Benchmark against C-Mod (opacity due to high density) and JET (opacity due to large size) Experimental involvement: C-Mod, JET Collaborators: D. Reiter, J. Terry, G. Matthews Category for 2004: P Report(2004)s: C-MOD(√), JET(√) 2005 proposal Experimental involvement: C-Mod, JET

Keypersons: D Reiter, J Terry, G Matthews, S Lisgo Category for 2005: E DSOL-6: SOL flow and influence on impurity shielding (Asakura) Goal: Comparison of SOL flows in a wide range of experiments with codes Areas of concentration

SOL flow measurements at many points in SOL, and determination of the flow pattern. Determination of influence of the SOL flow on impurity transport. Experiments to determine relationship of parallel flows to plasma rotation.

Experimental involvement: JT-60U, DIII-D, JET, C-Mod, TCV Collaborators: N. Asakura, G. Porter, K. Erents, B. LaBombard, J. Neuhauser, R.Pitts Category for 2004: P/(E) Report(2004): C-MOD (√), JET (√), ASDEX-Upgrade(√),TCV (√ ), JT-60U(√)

DSOL-7: Study on separatrix density and edge density profiles (Kallenbach)

Goal: Better characterize relationship between pedestal, SOL and divertor plasmas in ELMy H-mode

Areas of concentration Comparison of SOL and pedestal Te, Ti, ne profiles in ELMy H-mode plasma. Understanding of pedestal/separatrix densities, ne, Te, Ti gradients among differnt-scale tokamaks, which will determine the divertor performance in ELMy H-mode.

Experimental involvement: AUG, C-MOD, DIII-D, JET, JT-60U, MAST Collaborators: A.Kallenbach, N.Asakura, A.Kirk, A.Korotkov, M.A.Mahdavi,

D.Mossessian, G.D.Porter Category for 2004: P Report(2004): AUG(√), C-MOD(√), DIII-D (√), JET (√), JT-60U(√), MAST (√) 2005 proposal Experimental involvement: C-Mod, ASDEX-Upgrade, JET. Keypersons: 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)

Category for 2005: P DSOL-8 Radial ELM propagation (Counsell) Goal: better predict divertor and first-wall heat loadings during ELMs Areas of concentration

Investigation of heat and particle loading on the first wall, and poloidal and toroidal asymmetries.

Experimental involvement: AUG, DIII-D, JET, JT-60U, MAST Collaborators: G.Counsell, A.Herrman, W.Fundamenski, N.Asakura,

Fenstermacher/Leonard Category for 2004: (E) Report(2004): AUG(√), MAST (√), DIII-D (√), JET (√), JT-60U (√) 2005 proposal This work shifted to PED-10 with including IRTV data.

DSOL-9 C-13 injection experiments to understand C migration (Philipps) Goal: better predict carbon redeposition and T-retention in VV Areas of concentration Investigation of Local- and Long-range transport and mitigation in VV. Experimental involvement: AUG, DIII-D, JET, JT-60U Collaborators: Philipps, Coad/Rubel, Kirschner, Rohde, S.Allen, S.Higashijima Category for 2004: (P/E)

Report(2004): AUG(√), DIII-D (√), JET (√), TEXTOR(√), JT-60U (√) 2005 proposal

Experimental involvement: JET, DIII-D, TEXTOR, ASDEX-Upgrade, JT-60U, NSTX Keypersons: G.Matthews(JET), P.Stangeby (DIII-D), V.Philipps (Textor), K. Tsuzuk(JT-60U), V. Rohde, C. Skinner Category for 2005: E

DSOL10 Modeling of different gases effects on the power deposition (Whyte)

Goal: Reduction of disruption heat flux to divertor and wall with different impurity puff/ gas jet/ pellet

Experimental involvement: DIII-D, JT-60U, Tore Supra Collaborators: Contact persons: D. Whyte (UW-Madison), M. Bakhtiari (JT60-U), G.

Martin (Tore Supra) Category for 2004: (P) Report(2004): DIII-D(√), JT-60U(√), Tore Supra(√)

2005 proposal Experimental involvement: DIII-D, JET, C-Mod Keypersons: 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)

Category for 2005: P

DSOL11 Disruption mitigation experiments on JET and C-Mod (Whyte) Goal: Areas of concentration : Analysis of the effect of disruption mitigation on wall materials Experimental involvement: DIII-D, JT-60U, Tore Supra, JET Collaborators: D. Whyte (UW-Madison), T. Jernigan (ORNL), E. Hollmann (UCSD), M.

Bakhtiari (JT60-U), G. Martin (Tore Supra), V. Riccardo (JET), P. Andrew (JET), R. Granetz (MIT), K. Erents (JET), G. Matthews (JET), K.H. Finken (Juelich)

Category for 2004: (P) Report(2004): DIII-D(√), JT-60U(√), Tore Supra(√)

2005 proposal Keypersons: 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)

Category for 2005: E, recommended to combine MDC-1

DSOL12 Oxygen wall cleaning (Stangeby)

Proposal : Test of C and T removal at remote area 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.

Experimental involvement:DIII-D, TEXTOR, HT-7,( JET) Collaborators: P.Stangeby. V. Phillips, J. Li, G. Matthews Category for 2004: (P/E) Report (2005) DIII-D(√), TEXTOR(√), HT-7(√)

2005 proposal

Experimental involvement: TEXTOR, HT-7, DIII-D, AUG Keypersons: P.Stangeby (U of Toronto/GA/LLNL), V. Philipps (Textor), J. Li (Hefei,

HT-7), J. Roth (AUG) Category for 2005: E

DSOL13 Carbon deposition measurement in tile gap (Krieger) Proposal : Quantification of the total amount and spatial distribution of hydrocarbon layers in gaps

of plasma facing surfaces. Investigation of the dependency of deposition rates (on gap geometry, local plasma parameters, carbon concentration and surface temperature).

Experimental involvement: TEXTOR, ASDEX Upgrade, DIII-D Collaborators: Category for 2004: (P/E) Report(2004): TEXTOR, ASDEX Upgrade, DIII-D

2005 proposal Experimental involvement: AUG, TEXTOR, DIII-D, C-mod, Tore-Supra, JT-60U Keypersons: K. Krieger (ASDEX-Upgrade), A. Litnovsky (Textor), C. Wong (DIII-D), B.

Lipschultz (C-Mod), E. Tsitrone(TS), K. Masaki(JT-60U) Category for 2005: P

DSOL14 Benchmarking of Edge Simulation Codes Topical Group (Coster) Proposal : Disruption heat flux pattern to wall and divertor Experimental involvement: Codes only, AUG, JET so far Category for 2005: P Keypersons: D.Coster(JET/AUG), X.Bonnin, (H.Kawashima), T.Rognlien(LLNL), J.Strachan(JET), R. Pitts (TCV)

DSOL15 Inter-machine comparison of blob characteristics (Terry)

Proposal : Coordinated fast camera images acquisition across tokamaks. Comparison of blob characteristics

Experimental involvement: C-Mod, NSTX, TJ-II Category for 2005:E

Keypersons: J. Terry (C-Mod), S. Zweben (NSTX), C. Hidalgo (TJ-II), R. Maqueda (NSTX), O. Grulke

DSOL16 ICRH Wall conditioning for hydrogen removal (Ashikawa)

Proposal : Demonstration of efficient T removal method for ITER Experimental involvement: LHD, Tore Supra, HT-7 Category for 2005: proposed Keypersons: Ashikawa, Gendrih, Li

V. Meeting

The 5th ITPA Meeting on SOL and Divertor Physics Topical Group was held in 8 – 11, Nov. 2004, at Instituto Supereior Tecnico, Lisbon. Future plan of meetings • 6th ITPA SOL&divertor Physics TG meeting is expected just after 32th EPS conference,

(in Taragona, 4-7 July. 2005).

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

Meeting Participats in the 5th meeting: E.Tsitrone(EU), A.Loarte(EU), D.Coster(EU), G.Counsell(EU), R.Pitts(EU), M.Rubel(EU), K.Krieger(EU), V.Philipps(EU), A.Kallenbach(EU), Ph.Ghendrih(EU), B.Lipschultz(US), S.Krashnenikov(US), Max.Festenmacher(US), P.Stangeby(US), S.Lisgo(US), A.Mahdavi(US), R.Maingi(US), J.Strachan(US), R.Raman(US), A.Leonard(US), N.Asakura(JP), T.Tanabe(JP), S.Takamura(JP), N.Ohno(JP),, N.Ashikawa(JP),G.Kirnev(RF), ,S.W.Yoon(CN), S.H.Hong(CN), K.S.Chung(CN),T.D.Pan(CN), M.Shimada(IT), A.Kukushkin(IT), A.Polovei(IT) Short summary of the 5th meeting: There were 33 participants from EU(10), JP(5), US(10),RF(1), CN(4), IT(3 (1) Central focus of the Lisbon meeting was recent modeling status.

• modelling codes have many parameters that are set differently by different ‘operators’ leading to different results: flux limiting heat flow, Mach limit at plate, grid edge boundary conditions…

• Code-code comparisons is very useful: long-term testing is planned. • Improvements in codes being pursued as well

α: handle 2nd separatrix and grid to walls,

high density divertor (e.g. Ly absorption…)

(2)

• onfirmed by spectroscopy and 13C

• . Higher Mach

•

SOL flow measurements and understanding of the driving mechanism were progressed.

Subsonic SOL flow (plasma & carbon) was cdeposition other than Mach probe measurements. Stagnation point of the parallel flow was shifted to outer (LFS) SOLnumber and lower plasma pressure at inner (HFS) SOL were observed. Driving mechanism was proposed by combination of perpendicular transport and

poloidal drifts, which will influence on predictions of C-deposition, T-retention, impurity concentration.

(3)

• deposition in JET, ASDEX-Upgrade, DIII-D shows

• 13C trace experiments from the outer divertor is under investigation (JET, JT-60U).

(4)3 -1

• CTs show better efficiency: but tentative CT is small size, problems of penetration and

(5) DSOL proposals of IEA/ITPA experiments/study increased from 7(2004) to 15. ) Arrangement of sections in Chapter 4 “Power and particle control” in “The Tokamak Physics Basis” was discussed.

Impurity tracer experiments ((13C ) were reviewed.

All results of the long-range carbon the subsonic flow to inner divertor.

Fueling status was reviewed for the first time.

High-field pellet injection is a primary• choice for larger than 20Pam s . ELM triggering/mitigation has been progressed.

• SMBI (Supersonic jet) is good efficiency. However, compatibility with ELM and high ne plasma should be studied.

impurity.

(6

VI. Annual report of progress:

There was one TG meeting between form June 2004 and June 2005, and summary of the 5th is highlighted as followings,

(1 plex 2D codes.

s m

ct

• • nces of atomic/molecule processes (n-n collisions, Lyα absorption,

s/electrons, impurity and

als transport needs to be included. e)

• Extension of the calculation up to the first wall

ent comparison

ITPA Meeting on SOL and Divertor Physics Topical Group (1)Critical issues and Recent modeling status for ITER

-1) Critical issues in SOL & Divertor modelling in ITER Modelling of ITER SOL & divertor is performed using comAreas where physical process or modelling assumptions in ITER are unjustified are u marized in order to provide more reliable predictions.

• Description of the anomalous diffusion model should be introduced: this effeinfluences heat & particle fluxes asymmetry and neutral recycling. Modelling of SOL flow and drifts influences on in/out asymmetry, material transport. Experimental evideHe-D elastic collision, etc) will improve these modeling determining ITER detached divertor condition.

• Kinetic effect corrections to parallel transport (Energic ionELM) need to be included.

• Hydrocarbon & their radic• Divertor shape (V-shape, Gas conductance, Dom• Second separatrix effects

• Wall saturation and pumping • Wall material (mixture material case)

(1-2) Modelling, Code-code comparison, Code and experimCompare the EDGE codes for a series of cases with increasing physics processes, in order

to understand the origin of differences and to validate codes. (1-

• Bs

s. Having the same flux limiter choice in two closer together.

Density scan (better agreement at low n ), inclusion of drifts (still unstable solution),

on. (1-2

particular, at high

2-1) Benchmark work started from 2005 in DSOL-14: enchmark work of SOLPS(B2-EIRENE) vs EDGE2D-NIMBUS with same grid and

ame plasma conditions has been in progress: Initial results were substantially different due to different assumptions about kinetic

parallel electron and ion energy flux limiterboth codes brought the

e

and C-impurity (in progress) started.

• UEDGE is added so

-2) Results and future work on code and experiment comparison: Drifts and impurity

In-out asymmetry• in divertor plasma was enhanced with including drifts (B2 in JET, AUG, EDGE2D in JET, UEDGE in DIII-D): ExB and grad-B play an important role.

• Shift of divertor plasma peak, Dα & impurity emission profiles are consistent with measurements.

• Agreements between simulation and measurements are generally good for attached divertor, but large differences in detached plasma.

• Steady-state solution (conversion) for drift-ON case is still difficult, in density and in H-mode.

n coefficient may be different for low- and high-Z. DIII-D modelling can

• N

• hich is covered in DSOL-5: divertor plasma

rtor pressures by the factor of ~5 due to careful modeling of

t (implications for , neutral viscosity,

(1-2-3) Role of divertor geometry

ment:

• mping: ely to optimise D/T and recycling impurity

• affected by divertor closure. But maximum determined by

.

• Diffusioreproduce spectroscopy results (D~0.4 for C6+, D~0.7 for C2+). Wall pumping needs to be included, which may influence detachment.

eutrals UEDGE modelling of C-Mod divertor, wwith diffusive neutrals and radiation absorption (need high n0L to be ITER-like). Although previous attempts failed to match divertor pressure to factor of 10 lower, new results increased divebackground plasma and neutral transport.

• Several effects of neutral atom/molecule were found to be importanITER): Photon transport (Ly-series absorption in detached divertor)ion-neutral collisions.

Common understanding of divertor geometry effects was summarized:

• Heat load reduction: Effects of divertor geometry on target power load: vertical target is preferable.

• Radiation enhance Closed divertor geometry enhanced radiation enhancement (AUG), but not at JET.

Particle control &pu Divertor geometry can be used effectiv

pumping. Neutral control: Neutral compression can be separatrix locations

• Detachment : Spatial variation and detachment threshold for pl asma detachment along divertor target

rtor geometry. However, complete detachment and density

•

and impurity shielding

(2)SO ssed. (2-1) SOL flow measurements and the driving mechanisms

or

P Geometry effect: upper and lower null

er&outer midplane)

• Inve (i) “D -60U) was not enough

rd pinch increases M// to subsonic level (EDGE2D). t increase,

tor?

that high plasma pressure at outer SOL, and low pressure at inner SOL. Thus, poloidal pressure asymmetry drives flow from outer to

n level.

(2-2) Ca n an tritium retention. Local dep

• t s man sults w ted.

tion AT 1.3x1023C plasma top (2001) OH Analyzed

can be influenced by divelimit 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

are very minor, besides increased pumping of recycling impurities.

L flow and long range transport of carbon : SOL flow measurements and understanding of the driving mechanism has progre

• New results (drift, geometry, impurity flow) were reported in JET, TCV, C-MOD, DIII-D: all results showed subsonic SOL flow (M//~0.3-1.0) from LFS to HFS divertfor the ion grad-B drift towards the divertor.

ower scan and Bt reversal experiments in JET (measurement at plasma top), Impurity flow in DIII-D (at plasma top),

configurations in TCV (at outer midplane), upper/lower/double null configurations in C-MOD (inn

stigation of driving mechanism of subsonic flow in main plasma was in progress rifts” in simulation (EDGE2D, B2 in JET, UEDGE in JT

(2-5 times smaller) to explain subsonic flow in main SOL. (ii) Poloidal asymmetry in diffusion coefficient (D~1/Ba) increases M// (EDGE2D and

B2). (iii) Outwa

* However, physics model is not understood. M// at separatrix does nowhere is the source of C that flows to the inner diver

• Subsonic flow may be driven by asymmetries in perpendicular transport (C-MOD): Mach probe measurements showed

inner SOL Double null geometry experiment showed low ne, Te and fluctuatio Classical drifts also play a role to modify the flow pattern.

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

Carbon transport in SOL and migration rbon deposition (locatio d amount) influences

osition process were discussed in the 4th ITPA meeting (Naka, Jan. 2004). Long and short range transport of carbon in SOL has been investiga ed using trace gapuffs (13CD /4

13CH4

) in y tokamaks. The re ere repor

Tokamak Total injec Puff location Target plasma nalysis JE

4.2x1023C outer divertor(2004) H-mode Progress AUG 0.9x1022C outer midplane(2002-3) ELMy-H Analyzed

DIII-D 1x1022C plasma top(2003) L-mode newly analyzed

• (probe) is consistent with CII & CIII distribution measurements (DIII-D).

ith M//~0.5 due to large friction force towards the di hielding from the core plasma is improved).

t

mary

where Dped=0.03-0.1,) is needed to maintain n ~1020m-3 (~ASTRA cal.)

(3- Part ized in SOL in ITER simulation, thus very low fuelling efficiency (K udivertor plasma is extended at higher density. (3-2)P

3 -1

•

HD active

He e

tter choice for SS operation with less fuelling.

• wa

(3- SMB is getting popular ( HL-1M, HL-2A, W7-AS, AUG, ToreSupra).

ToreSupra: systematic study of LFS & HFS SMB (200Pam3s-1 in 2ms, Mach ~5) was

m-3, power(LH) = 0-5MW), and it was comparable between LFS and HFS.

TEXTOR 7x1020C limiter top (2004) L-mode newly analyzed JT-60U 3x1023C outer divertor(2004) L-mode Progress

Subsonic flow towards Inner divertor was confirmed experimentally and numerically: M//~0.4-0.5

• Impact on impurity shielding (core plasma) and carbon deposition in divertor (DIII-D): C ion density at separatrix (CXR) was consistent with simulation w

vertor (s 13C deposition pattern was consistent with M//~0.5 case: C ions deposit near strike-poin

(3) Fuelling sum Fueling status in the existing tokamaks was reviewed, for the first time.

A fuelling rate of Γcore =20-90Pam3s-1 (core

1) Gas puff

icles are mostly ionuk shkin): Γcore < 20 Pam3s-1 and nse < 4x1019m-3 (B2-EIRENE cal.), and detachment of the

.

ellet: • FS injection is available fuelling method to obtain 20-80Pam s for Inductive/Hybrid

operation in ITER. HFS injection experiments (AUG) evaluated pellet size for ELM triggering: d > 0.6mm

H

was enough. For ITER, d > 4mm with V > 0.5km/s would be enough to penetrate into Mregion of pedestal plasma.

• Pellet injection for ELM mitigation was evaluated for ITER (Polevoi, et al.), based on JT-60U, DIII-D, AUG HFS pellet experiments: HFS PI is better effect, but enhances n /n to 2-9% due to core fuelling.

• LFS Pellet injection will be be • Steady-state ne control during 2 min (155 pellets) in ToreSupra (also using LH

notching) Wall retention was comparable to gas puff (T-S) due to limiter operation? – effects on

ll pumping and recycling flux should be confirmed.

3)Supersonic Molecular Beam

•performed. Fuelling efficiency (40-60%) did not decrease with ne= 3-7x1019

However, influence on SOL plasma (Isat increased, Te decreased, and M// changed) ng efficiency decreased from 30% (OH, L-mode, Type-III H-mode) to • AUG : fuelli

~10% in 5MW NB ELMyH-mode (6x1019m-3: high ne and ELM).

• Whereas efficiency was reasonable so far, compatibility in ELMy H-mode, distance to plasma, and influence on SO /detachment should be investigated.

(3-

T injection into Tokamak discharges were demonstrated in TdeV(0.16MA/1.4T),

•

etc. (tentative size

m electrode was another concern.

ction velocity and length, which is attractive for

• is planned in 2007-8. Design work was finished in JT-60U/JET, and ITER (20cm dia. and length, 1023m-3,

(3-5)W m saturated wall

• steady-state operations (3 hours discharge ntrol by water cooling (<100C) sup ressed neutral

lse

r shielding sity regime (ne/n

GW>0.3-0.4) should be

) Remaining issues for next meetings.

th

High-Z experience (updated from 5 meeting) • First wall loadings & joint meeting with MHD (joint session with MHD TG)

e and W)

ffects on the divertor performance (7) Contribution to 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.

L

4)CT injection CJFT2M(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,experiment), whereas injection velocity was fast (a few 100km/s).

• Metal fro

• Potential capability to control injeprofile 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)•

<20Hz)

all fuelling fro Wall fuelling was pointed out in the previous

in TRIAM-1M). Wall temperature co pflux from co-deposited layers of Mo+O (D/Mo~0.35), extending the long puoperation up to 5 hours using gas puff FB.

• Change in wall pumping/fuelling with surface temperature, and SOL/divertowith active divertor pumping in normal deninvestigated.

(6• D/T inventories (surfaces and sides of tiles) and removal (updated from 5 meeting) • Dust (model of movement + summary of existing knowledge) • th

• Mixed materials effects (with B• Estimate of the effects of Be operation in ITER • Discussion of ITER dome and e

VII. Future plan of publications • Chapter 4 “Power and Particle Control” in The Tokamak Physics Basis”. Status of chapter 4 is as following,

Appendix A

IV. Status and proposals for ITPA/IEA work:

According to suggestions from ITPA/IEA committee members, (i) to separate a group of topics to different proposals, and (ii) to combine with similar PEP proposals. Reports from DSOL-1 to DSOL-7 in 2004, and new proposals from DSOL-8 to DSOL-14 were discussed in the 5th ITPA meeting in Losbon, Nov. 2004. DSOL15 is proposed as a new plan. DSOL-1: Scaling of type I ELM energy loss (Loarte/Leonard)

Goal: better predict divertor and first-wall heat loadings during ELMs Areas of concentration: Determination of ELM divertor heat pulse shape, timing and amount, and appropriate model to extrapolate to ITER operation regime. Experimental involvement: JET. DIII-D, JT-60U, ASDEX-Upgrade Collaborators: A. Loarte, T. Leonard, N.Oyama, Kallenbach Category for 2004: P Report(2004): AUG(√), DIII-D(√), JET(√), JT-60U(√) Database fis sheared with PEP-2. Analysis of pedestal plasma characteristics shows that the pedestal temperature width

scales as expected from plasma physics dominating the gradients while the pedestal density seems better correlated with ionisation physics dominating this width. ρ* scaling of the ELM energy loss in the JET and DIII-D experiments produces opposite results : no ρ* scaling of the ELM energy loss at JET, while a large dependence of ρ* on the ELM energy loss is identified in DIII-D. No clear explanation for this difference has been identified so far, but it is believed to be due to the very low level of input power used in the DIII-D experiments for the large ρ* discharges. This is in agreement with various JET experimental results. A series of experiments to compare JET and JT-60U experiments with dimensionally similar pedestal plasmas has been performed but a detailed comparative study of ELM characteristics has not been done yet.

2005 proposal New title: Disruption energy balance in similar discharges in the ITER QDT = 10

scenario(A. Loarte, D. Humphreys, G.Pautasso) Experimental involvement: JET, DIII-D, ASDEX Upgrade, MAST, JT-60U Keypersons: A. Loarte, P. Andrew, V. Riccardo, A. Kellman, D. Humphreys, G.Pautasso, G.

Counsell, D. Whyte, K. Tsuzuki,A. Herrmann Category for 2005: E Plan: 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) Goal: better determine chemical sputtering yield in tokamaks

Areas of concentration Predict the parameter dependence of chemical yield in ITER carbon divertor

Experimental involvement: AUG, JET, TEXTOR, JT-60U, DIII-D Collaborators: V. Phillips, D. Whyte, G. Federici, P. Coad, P. Ghendrih, R. Neu, V. Rohde,

B. Lipschultz, J. Davis, S. Higashijima

Category for 2004: P/(E) Report(2004): AUG(√), JET(√), TEXTOR (√), DIII-D(√), JT-60U(√) Flux dependence of CD4 was updated (CD4 yield decreases with Γdiv >6x1021m-2s-1 2005 proposal Experimental involvement: TEXTOR, JET, AUG, DIII-D, JT-60U Key-persons: V. Philipps (FZJ Juelich) S. Brezinsek (FZJ Juelich), M.Stamp (JET), R.

Pugno (AUG), T.Nakano (JT-60U), M.Fenstermacher (DIII-D) Category for 2005: E Plan: 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 divertors)

DSOL-3: Scaling of radial transport (Lipschultz) Goal: better predict divertor & first-wall power/particle loadings Areas of concentration Develop same measurements techniques for SOL profiles of ne, Te, SIon

Collection of dimensionlessly similar and dissimilar discharges for analysis Experimental involvement: C-MOD, DIIID, JET, JT-60U, MAST, NSTX Collaborators: B. Lipschultz, D. Whyte, G. Matthews, R. Pitts, G. Counsell, A. Kallenbach Category for 2004: (E) Report(2004): C-Mod (√ & planned), DIIID (√ & planned), JET (√) Flat profile at far SOL may be caused by opacity of neutrals in SOL. 2005 proposal Experimental involvement: C-Mod, JET, DIII-D, MAST, AUG Keypersons: B.Lipschultz (C-Mod), G.Matthews (JET), T.Leonard (DIII-D), S. Lisgo

(MAST), A. Kallenbach (AUG), R. Pitts (TCV) Category for 2005: E Plan: Investigate turbulence and time-averaged plasma data in extending devices(MAST, AUG,

TCV),

DSOL-4: Disruption energy balance in similar discharges (Matthews to Loarte) Goals: Better characterize divertor/first-wall heat loading Understand if there are any size effects on the division of power loadings Evaluate the performance of different materials for divertor/first-wall Areas of concentration: Comparison of heat deposition time and profile, radiation during thermal quench in

multi-machines (over various disruptions: beta-limit, high-density, Locked-mode, etc.). Experimental involvement: AUG, DIII-D, JET, MAST, TEXTOR, TCV, C-Mod Collaborators: D. Whyte, G. Federici, G. Matthews, R. Pitts, A. Mahdavi, A. Herrmann, R.

Granetz, G.Counsell, V. Riccardo, K.H. Finken Category for 2004: P Report(2004): AUG (√), DIII-D(√), JET√), MAST (√), TEXTOR (√), FTU(√) Analysis of the energy balance and timescales for energy fluxes during similar

disruptions has been carried out. (a) The thermal energy of the plasma at the thermal quench is significantly lower than

that during the full performance phase of the discharge for most disruptions, typically by a factor of 2 to 4.

(b) There is a favourable size scaling of the timescale for energy flux to PFCs during the thermal quench, but there is a significant spread in this timescale (by factors of ~ 6) and a large variation disruption-to-disruption for nominally identical discharges.

There is a significant broadening of the heat flux during the thermal quench (by a factor of 5-10) in diverted discharges. This seems to be absent in limiter disruptions (TEXTOR). While this alleviates the problem of energy deposition at the ITER divertor, it leads to significant energy flux reaching components (Be-clad blanket modules) on which no significant disruptive energy flux was expected previously.

2005 proposal Experimental involvement: JET, DIII-D, ASDEX Upgrade, MAST, JT-60U Keypersons: A. Loarte, P. Andrew, V. Riccardo, A. Kellman, D. Humphreys, G.Pautasso,

G. Counsell, D. Whyte, K. Tsuzuki,A. Herrmann Category for 2005: E Plan: 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. DSOL-5: Role of Lyman absorption in the divertor (Reiter) Goals: Understand whether Lyman absorption is important to include in fluid models Areas of concentration: Develop EIRENE to handle radiation transport Benchmark against C-Mod (opacity due to high density) and JET (opacity due to large size) Experimental involvement: C-Mod, JET Collaborators: D. Reiter, J. Terry, G. Matthews Category for 2004: P Report(2004)s: C-MOD(√), JET(√) Code development BGK-like photon transport was completed (pressure, Doppler and

natural broadening). C-MOD: strong global trap of Lya (90%), and weak trap of Lyε(15%), then divertor nD

reduced 1.8 times. 2005 proposal Keypersons: D Reiter, J Terry, G Matthews, S Lisgo Experimental involvement: C-Mod, JET Category for 2005: E Plan: ･ 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: SOL flow and influence on impurity shielding (Asakura) Goal: Comparison of SOL flows in a wide range of experiments with codes Areas of concentration

SOL flow measurements at many points in SOL, and determination of the flow pattern. Determination of influence of the SOL flow on impurity transport. Experiments to determine relationship of parallel flows to plasma rotation.

Experimental involvement: JT-60U, DIII-D, JET, C-Mod, TCV Collaborators: N. Asakura, G. Porter, K. Erents, B. LaBombard, J. Neuhauser, R.Pitts Category for 2004: P/(E) Report(2004): C-MOD (√), JET (√), ASDEX-Upgrade(√),TCV (√ ), JT-60U(√)

JET: Systematic scan of density and power for normal and reversed Bt(and Ip) plasmas. In-out asymmetry in heat flux, particle flux is consistent with simulations with EDGE-2D including drifts.

C-MOD: Flow and SOL plasma measurements in High- and Low-Field-side. In-out asymmetry of the plasma pressure may be a mechanism to drive the subsonic flow from LFS to HFS.

AUG: Midplain Mach probe shows flow toward plasma top, which consistent with other results (flow from LFS to HFS).

TCV: Midplain Mach probe measurements in systematic scan of plasma configuration (Z, divertor connection length) in normal reversed Bt condition,

JT-60U: Pumping from divertor and gas puff of H2 and CH4 were performed to investigate impurity shielding.

This proposal was closed (at least) in 2005, due to analysis of data with simulation.

DSOL-7: Study on separatrix density and edge density profiles (Kallenbach)

Goal: Better characterize relationship between pedestal, SOL and divertor plasmas in ELMy H-mode

Areas of concentration Comparison of SOL and pedestal Te, Ti, ne profiles in ELMy H-mode plasma. Understanding of pedestal/separatrix densities, ne, Te, Ti gradients among differnt-scale tokamaks, which will determine the divertor performance in ELMy H-mode.

Experimental involvement: AUG, C-MOD, DIII-D, JET, JT-60U, MAST Collaborators: A.Kallenbach, N.Asakura, A.Kirk, A.Korotkov, M.A.Mahdavi,

D.Mossessian, G.D.Porter Category for 2004: P Report(2004): AUG(√), C-MOD(√), DIII-D (√), JET (√), JT-60U(√), MAST (√)

Analysis results were presented by Kallenbach, et al. in 2004 PSI “Multi-machine comparisons of H-mode separatrix densities and edge profile behaviour in the ITPA SOL and Divertor Physics Topical Group”. Database was transfer to MDSplus three in collaboration with the Pedestal Topical Group.

2005 proposal Experimental involvement: C-Mod, ASDEX-Upgrade, JET. Keypersons: 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)

Category for 2005: P Plan:

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 ELM propagation (Counsell) Goal: better predict divertor and first-wall heat loadings during ELMs Areas of concentration

Investigation of heat and particle loading on the first wall, and poloidal and toroidal asymmetries.

Experimental involvement: AUG, DIII-D, JET, JT-60U, MAST Collaborators: G.Counsell, A.Herrman, W.Fundamenski, N.Asakura,

Fenstermacher/Leonard Category for 2004: (E) Report(2004): AUG(√), MAST (√), DIII-D (√), JET (√), JT-60U (√) Large transient radial flux was observed up to close to wall: 30cm (MAST), 10 cm

(AUG). Radial velocity was estimated to 0.4km/s (AUG), 1km/s (MAT, JET). Dependence of the plasma parameters: Bt dependence, was measured in AUG. Heat flux of kulti-peaks in divertor footprint show n=8-15.

2005 proposal: This work shifted to PED-10 (2005) with including IRTV data.

DSOL-9 C-13 injection experiments to understand C migration (Philipps) Goal: better predict carbon redeposition and T-retention in VV Areas of concentration Investigation of Local- and Long-range transport and mitigation in VV. Experimental involvement: AUG, DIII-D, JET, JT-60U Collaborators: Philipps, Coad/Rubel, Kirschner, Rohde, S.Allen, S.Higashijima Category for 2004: (P/E)

Report(2004): AUG(√), DIII-D (√), JET (√), TEXTOR(√), JT-60U (√) Tokamak Total injection Puff location Target plasma Analysis JET 1.3x1023C plasma top (2001) OH Done 4.2x1023C outer divertor(2004) H-mode Progress AUG 0.9x1022C outer midplane(2002-3) ELMy-H Done DIII-D 1x1022C plasma top(2004) ELMy-H Done TEXTOR 7x1020C Limiter top (2004) L-mode Done JT-60U 3x1023C outer divertor(2004) L-mode Progress 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.

2005 proposal

Experimental involvement: JET, DIII-D, TEXTOR, ASDEX-Upgrade, JT-60U, NSTX Keypersons: G.Matthews(JET), P.Stangeby (DIII-D), V.Philipps (Textor), K. Tsuzuk(JT-60U), V. Rohde, C. Skinner Category for 2005: E Proposal:

Fast 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.

DSOL10 Modeling of different gases effects on the power deposition (Whyte)

Goal: Reduction of disruption heat flux to divertor and wall with different impurity puff/ gas jet/ pellet

Experimental involvement: DIII-D, JT-60U, Tore Supra Collaborators: Contact persons: D. Whyte (UW-Madison), M. Bakhtiari (JT60-U), G.

Martin (Tore Supra) Category for 2004: (P) Report(2004): DIII-D(√), JT-60U(√), Tore Supra(√) - Radiation calculations, benchmarked against present DIII-D and JET experiments, have

shown that a uniform, rapid radiative shutdown of a Q=10, 15 MA ITER plasma will likely result in a uniform but thin (~10-50 microns) melt layers of the beryllium first wall. This constitutes a possibly significant quantity (10’s of kg) of mobile, molten Be and is a result of the low melting temperature of Be. Melting will not occur if the induced thermal quench can be stretched to longer timescale (> 5 ms) and be kept spatially uniform.

- Radiation calculations have demonstrated the possibility to use surface heating from planned rapid radiative termination to recovery tritium from surface films containing trapped hydrogenic fuel.

- JT-60U showed that combining low-Z H2 gas with the noble gases (He, Ar, Ne) proved more efficient at suppressing runaway electrons, which pose a threat of localized power loads when lost to the wall in ITER.

- ToreSupra confirmed efficiency of He gas injection for runaway suppression.

2005 proposal Experimental involvement: DIII-D, JET, C-Mod Keypersons: 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)

Category for 2005: P Proposal: A wide range of scenarios with different gases and injection rate need to be explored to

optimize thermal mitigation, runaway suppression and rapid radiative surface heating for tritium recovery in ITER.

DSOL11 Disruption mitigation experiments on JET and C-Mod (Whyte)

Goal: Areas of concentration : Analysis of the effect of disruption mitigation on wall materials Experimental involvement: DIII-D, JT-60U, Tore Supra, JET Collaborators: D. Whyte (UW-Madison), T. Jernigan (ORNL), E. Hollmann (UCSD), M.

Bakhtiari (JT60-U), G. Martin (Tore Supra), V. Riccardo (JET), P. Andrew (JET), R. Granetz (MIT), K. Erents (JET), G. Matthews (JET), K.H. Finken (Juelich)

Category for 2004: (P) Report(2004): DIII-D(√), JT-60U(√), Tore Supra(√) - DIII-D, Tore Supra and JT-60U implemented and experimented with large gas injection systems for disruption mitigation.

- Empirical studies on the suppression of runaway electrons (RE) show that if smaller quantities of pure noble gas are injected then RE are measured in the current quench. These results are in quantitative agreement with modeling of the CQ evolution.

- DIII-D has tested a gas jet “directed” at the plasma center, but with a small entry tube (diameter ~ 1.5 cm) compared to the previous “open” jet (diameter ~ 15 cm). The new design allowed for better diagnostic access, but slower time response and a lower gas pressure/gas inventory (factor of 3-5). The principal result was that reduced gas jet pressure/inventory led to longer delays in initiating the thermal quench and allowed somewhat more RE in the current quench. This demonstrated that having high gas jet pressure seems to be most important factor in establishing reliable, rapid disruption mitigation.

- Studies on DIII-D suggest that injected gas jets of neon/argon are not fully penetrating to the central plasma as neutrals, but rather with a mixture of partial neutral penetration and MHD mixing. The thermal mitigation effectiveness remains >95% (i.e. energy radiated from core / initial plasma energy > 0.95) despite the partial neutral penetration. The scaling of this efficiency to ITER remains a key question awaiting cross-device comparison, but this new observation may reduce the pressure requirements for an ITER jet.

2005 proposal Experimental involvement: DIII-D, JT-60U, Tore Supra, JET, Alcator

C-Mod,TEXTOR, AUG Keypersons: 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)

Category for 2005: E, recommended to combine MDC-1 Proposal: Cross-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. DSOL12 Oxygen wall cleaning (Stangeby)

Proposal : Test of C and T removal at remote area 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.

Experimental involvement:DIII-D, TEXTOR, HT-7,( JET) Collaborators: P.Stangeby. V. Phillips, J. Li, G. Matthews Category for 2004: (P/E) Report (2005) DIII-D(√), TEXTOR(√), HT-7(√)

Oxidation experiments have been carried out in several tokamaks with C-removal rates up to 0.2 gm/hr. More detailed, quantitative studies are planned. Neither problems of recovery of plasma operation nor long term damage to internal components has been reported.

(a) TEXTOR. (V. Phillips) Interior: ~6 m2 graphite (limiters), ~35 m2 inconel. Completed and reported [J Nucl Mater 266-269 (1999) 386]: O2-baking at pressures up to 32 Pa and wall temperatures up to 700K. Maximum removal rate of C as CO and CO2: ~0.2 gm/hr. Good plasma operation recovered after GDC in D2 and He. No damage to internal components found since 1998 O2-bake. Plans: use RF plasmas, B ≠ 0, in He/O mixtures also standard He/O GDC to compare with O2-bake; insert pre-characterized surfaces at 3 locations in TEXTOR to quantify the removal by post mortem analysis and to compare with the more global analysis using RGA. Will study ozone exposure in lab experiments to remove C-deposits from TEXTOR tiles.

(b) HT-7. (J. Li) Interior: ~2 m2 graphite (limiters), ~10 m2 steel walls. Completed (in 2004): compared O2-baking, O-ICR exposure and O-GDC at ~450K, i.e. substantially cooler than used in TEXTOR. Not surprisingly, the C-removal rate by O2-baking was much less than in TEXTOR, by ~2 orders of magnitude. Very encouragingly, however, the removal rate by O-ICR and O-GDC was ~same as for O2-baking in TEXTOR, despite the substantially lower temperature. Plasma operation was recovered after a few hours of plasma shots and no damage to the torus was observed.

(c) DIII-D. (P. Stangeby) Interior: ~100% graphite. Plans: in 2005, puff 13CH4 into repeat Hmode shots, creating isotope-marked co-deposits; remove set of tiles and measure 13C deposits on faces and sides (tile-gaps); then expose tiles to O2-baking in lab to quantify removal rate for different deposit types as function of baking parameters.

(d) (JET). (G. Matthews) Accidental air-bakes over past ~20 years have not resulted in identified damage; a beneficial effect has been found: insulators, which had become conducting after long use in the vessel, recovered their insulating properties.

2005 proposal

Experimental involvement: TEXTOR, HT-7, DIII-D, AUG Keypersons: P.Stangeby (U of Toronto/GA/LLNL), V. Philipps (Textor), J. Li (Hefei,

HT-7), J. Roth (AUG) Category for 2005: E Proposal: DIII-D work plans given above in report.

DSOL13 Carbon deposition measurement in tile gap (Krieger)

Proposal : Quantification of the total amount and spatial distribution of hydrocarbon layers in gaps

of plasma facing surfaces. Investigation of the dependency of deposition rates (on gap geometry, local plasma parameters, carbon concentration and surface temperature).

Experimental involvement: TEXTOR, ASDEX Upgrade, DIII-D Collaborators: Category for 2004: (P/E) Report(2004): TEXTOR, ASDEX Upgrade, DIII-D TEXTOR: Matrix of 8×6 cells, 1×1×1cm TZM monoblocks, gap width 0.5mm, Exposure for

~560 s with average D-fluence 5×1019/cm2 in deposition-dominated SOL region -> 30% of deposited D in gaps, Deposition deeper in gaps for exposure in erosion

dominated SOL zone ASDEX Upgrade: 6×6 mm - gap size 0.5 mm, Exposed for ≈ 246 s -> e-folding length

2-3mm, 60% fraction of D deposited in gaps DIII-D: DIMO probe was used. Exposure ≈31 s Ohmic plasma sample at room temperature

-> e-folding length ≈ 5 mm D/C ≈ 0.52, -> Exposure at 150ºC not yet analysed

2005 proposal Experimental involvement: AUG, TEXTOR, DIII-D, C-mod, Tore-Supra, JT-60U Keypersons: K. Krieger (ASDEX-Upgrade), A. Litnovsky (Textor), C. Wong (DIII-D), B.

Lipschultz (C-Mod), E. Tsitrone(TS), K. Masaki(JT-60U) Category for 2005: P Proposals: AUG: 2x2 monoblock probe with variable gap width for exposure at divertor/OSP TEXTOR: New monoblock matrix with variable gap width DIII-D: Gap probe exposures with different plasma conditions C-Mod: Study sides of tiles removed from machine. New W rod tiles inserted for measurement in late 2005, early 2006.

DSOL14 Benchmarking of Edge Simulation Codes Topical Group (Coster) Proposal : Disruption heat flux pattern to wall and divertor Experimental involvement: Codes only, AUG, JET so far Keypersons: D.Coster(JET/AUG), X.Bonnin, (H.Kawashima), T.Rognlien(LLNL), J.Strachan(JET), R. Pitts (TCV) Category for 2005: P 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).

DSOL15 Inter-machine comparison of blob characteristics (Terry)

Proposal : Coordinated fast camera images acquisition across tokamaks. Comparison of blob characteristics

Experimental involvement: C-Mod, NSTX, TJ-II Keypersons: J. Terry (C-Mod), S. Zweben (NSTX), C. Hidalgo (TJ-II), R. Maqueda (NSTX), O. Grulke

Category for 2005:E Proposal: Collect images/movies from a range of collisionality plasmas and compare blob size, velocities, general characteristics.

DSOL16 ICRH Wall conditioning for hydrogen removal (Ashikawa)

Proposal : Demonstration of efficient T removal method for ITER Category for 2005: proposed Experimental involvement: LHD, Tore Supra, HT-7 Keypersons: Ashikawa, Gendrih, Li Proposals: Working 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.