V.Philipps, EFPW Padua, Dec 2005 Introduction Report on the European Task Force on Plasma Wall Interaction 2005 V. Philipps, J. Roth, A. Loarte on behalf of the EU- PWI TF members Introduction: ITER, PWI & fusion Report on 2005 work Summary and outlook V.Philipps, EFPW Padua, Dec 2005

scientific case for the TF Rationale (EFDA): to provide ITER with information concerning lifetime- expectations of the divertor target plates and tritium inventory build-up rates in the foreseen starting configuration and to suggest improvements, including material changes, which could be implemented at an appropriate stage and to improve the efficiency of work by synergies which are to be executed from the expansion of the work of individual tasks to the operation of all European devices EU TF Plasma Wall Interaction First EU Task Force,formed end of 2002

V.Philipps, EFPW Padua, Dec 2005 PWI will become a key issue in future due to much larger particle fluencies much larger power densities in transients energy input: 1 ITER pulse about JET years divertor ion fluence: 1 ITER pulse about 4 JET years stored energy: ITER about 100 x JET T-retention & wall lifetime will become critical PWI & Fusion Most of PWI and plasma experience is with graphite walls selection of first wall materials was determined by optimisation of plasma performance and flexibility

V.Philipps, EFPW Padua, Dec 2005 ITER 700m 2 Be first wall 100m 2 Tungsten 50 m 2 Graphite CFC Material selection determines largely - Critical PWI topics & EU-PWI-TF work programme ITER material selection Rationale for ITER material choice is to guarantee access to a broad range of plasma scenarios to confirm predictions on Fusion power, confinement, MHD, ELMs, ITB & current drive, disruptions, Power & particle exhaust

V.Philipps, EFPW Padua, Dec 2005 Working strategy Contact Persons in associations Definition of working topics, common experiments and data analysis by EU TF team and contact persons Special working groups (SEWG) SEWG meetings and general TF meetings (4) All reports and information on the PWI TF Web site

V.Philipps, EFPW Padua, Dec 2005 Organisation & work structure Work plan has been defined for each association topic association

V.Philipps, EFPW Padua, Dec Co-ordinated experiments in associations Fusion devices linear plasma machines lab experiments 2 EFDA PWI technology programme specific tasks integration of work outside associations 3 Integrated wall experiments in fusion devices Working strategy working topics, common experiments and data analysis

V.Philipps, EFPW Padua, Dec 2005 Seven topics defined 1.Erosion behaviour and impurity location (SEWG) report 2.Material transport and re-deposition report 3.Fuel recycling, retention and removal (2 SEWG) 4.Transient heat loads(SEWG) report 5.Edge & erosion and deposition modelling 6.Edge and SOL physics 7.Task force relevant diagnostics + SEWG on high Z plasma facing materials Organisation & work structure

V.Philipps, EFPW Padua, Dec Erosion behaviour & location Carbon chemical erosion under ITER conditions (SEWG) JET, AUG, TEXTOR, Tore Supra, PSI Berlin, Pisces Impurity production behaviour in the main chamber JET, AUG Influence of Be on chemical erosion of C EU-US technology task & IPP High temperature sputtering of W and Be EU-UU technology task, IPP Garching, FZJ, ENEA Characterisation of C/W/Be mixed-material formation EU-US technology task

V.Philipps, EFPW Padua, Dec 2005 FZJ: Erosion at test limiters in TEXTOR (high fluxes), D/XB calibration, ERO code modelling IPP: Synergistic erosion of H o with inert gases Erosion mitigation due to metal doping Erosion and deposition in ASDEX Upgrade Erosion and deposition in PSI-2 D/XB calib. UKAEA: chemical erosion at JET CEA: Chemical erosion on neutraliser plate CIEMAT: Influence of N 2 on C-erosion/deposition EU-US collaboration: PISCES-BInfluence of Be seeding collaboration through ITPA: JT60-U,DIIIDChemical erosion at divertor plates in future we hope also for contributions from Magnum linear device SEWG chemical erosion (S.Brezinsek/J. Roth) Main open question: chemical erosion yield of the ITER graphite target Carbon chemical erosion

V.Philipps, EFPW Padua, Dec 2005 Description of Y as function of Ion energy Surface temperature Ion flux Low yields under ITER divertor conditions further decrease by Be deposition open questions: Influence of surface conditions, redeposited layers, dependence on structure.. Chemical erosion Chemical erosion depends in a complex manner on ion flux, energy, surface temperature and condition

V.Philipps, EFPW Padua, Dec 2005 AUG experiments on chemical erosion No CD+ (420 nm) ! CH form CH 4 puff Chemical erosion under detached conditions ( Te< 2eV, Tsurf< 400K ) CH source from CH4 injection visible, D/XB values determined > intrinsic CH signal very low, at the detection limit low intrinsic erosion yield (details under analysis

V.Philipps, EFPW Padua, Dec 2005 JET experiments on chemical erosion C 2 H 4 injection in outer divertor with slow strike points sweeps attached conditions (Te>15eV) DX/B values from injection used for the reference discharge Most reliable value for Y chem is achieved withthe strike point at GIM10 injection Ychem from higher hydrocarbons about 2%

V.Philipps, EFPW Padua, Dec 2005 Introduction Fast decrease of C-erosion for comparably small Be plasma concentrations (upstream) Critical issue: thermal stability of Be layers EU-US collaboration (PISCES B, UCSD) Dependence of carbon chemical erosion Be plasma concentration 1. Erosion behaviour & location

V.Philipps, EFPW Padua, Dec 2005 XPS data shows surface layer is largely Be 2 C Virtually all C remaining at the surface is bound as carbide Presence of carbide inhibits chemical erosion of C Carbide layer reduces sputtering yield of bound Be Subsequently deposited Be can more easily erode XPS analysis of Be on C sample surface Much better understanding of chemical erosion behaviour but still open questions to be addressed

V.Philipps, EFPW Padua, Dec Material transport and re-deposition A main research topic of EU PWI TF Global and local material transport ways work in JET, AUG, TEXTOR, Tore Supra Quantitative erosion/deposition balances work in JET, AUG, Tore Supra, TEXTOR Dedicated deposition studies Quartz detectors, sticking monitors, temperature dependence work in JET, AUG, TEXTOR, PSI-2 Berlin Migration to gaps and hidden areas work in JET, AUG, TEXTOR, Tore Supra

V.Philipps, EFPW Padua, Dec 2005 Involved Associations 1. Fusion devices: AUG JET TEXTOR Tore Supra 2. Linear PSI devices PSI-2 Berlin PISCES-B future: Magnum 3. Several associations involved through post mortem surface and tile analysis VR Stockholm Tekes CNR Milano IFPILM Warsaw Jozef Stefan Institute-Ljubljana 2. Material transport and re-deposition

V.Philipps, EFPW Padua, Dec 2005 Erosion, deposition & material migration Main tasks: Global erosion/deposition material balances (AUG, JET, TEXTOR, Tore Supra) Growing understanding and data consistency Fuel retention: 1. From overall material deposition and associated fuel retention (T-codeposition) 2. From fuel balances Still a lack of consistency between both methods!! Needs further work

V.Philipps, EFPW Padua, Dec 2005 Neutralizers : ~10 g TPL : ~5.5 g Outboard movable limiter : ~1.5 g Net erosion estimate : 40 g 20 g maximum missing Tore Supra: Somewhat coherent carbon balance but overall carbon deposition not sufficient to explain D retention evaluated from fuel balances Antennas + launchers : ~1 g Erosion, deposition, example TS

V.Philipps, EFPW Padua, Dec 2005 Carbon is transported stepwise Final C- deposition pattern determined by plasma operation scenarios No significant long range transport of Be louver Quartz monitor C deposition Be deposition JET AUG Deposition probes beneath the divertor: strong decrease with temperature From re-erosion by D-atoms Work on understanding the mechanism of migration and deposition 2. Material transport and re-deposition

V.Philipps, EFPW Padua, Dec 2005 On plasma wetted areas, C is effectively transported by multi-step chemical erosion, promoting significant deposition in gaps (depending on geometry) In shadowed areas, C deposition is governed mainly by high sticking species (line-of-sight). Deposition is determined by competition with re-erosion by atomic hydrogen, only a minor fraction migrates longer distances Be does not show long range transport ITER: C- transport down the vertical target trapping in gaps & migration towards the PFR (dome ) Be- deposition on the vertical target some transport in the upper SOL & trapping in gaps 2. Material transport and re-deposition

V.Philipps, EFPW Padua, Dec 2005 Tritium retention mitigation and detritiation needed in ITER SEWG: fuel removal EU PWI activities Removal of carbon layers by oxidation: transformation of carbon in CO and CO 2 which is pumped out O 2 venting, GDC and ICRH plasmas in O 2 (AUG, TEXTOR) only remove C, contamination with O N 2 -seeding: prevent C deposition by scavenger action (Ciemat, AUG, JET) only remove C, effective enough? works only during deposition, N increase also C erosion Photocleaning: ablation of codeposits (lasers, flashlamps) UKAEA, JET, CEA, IFPILM Warsaw difficult access, production of dust

V.Philipps, EFPW Padua, Dec 2005 Several technology tasks in the field of T removal Optimisation of He-O Glow for C-H removal Characterisation PFC Oxidation Damage, T removal by non-O 2 oxidative methods T retention in ITER-like material mixes and T surf

V.Philipps, EFPW Padua, Dec 2005 simple and proven technique, Slow C removal rate 2.3x10 19 C/s (5.2 g C in total) GD C Integral data from QMS CO CO 2 HD A Kreter et al O 2 GDC in TEXTOR tokamak Depos. in H 2 /CH 4 GD Cleaning in 5%O 2 /He GD After 45 GDC, 75 % of hydrogen released Some cleaning of gaps possible, needs further work Cleaning of gaps by O 2 GDC (Ciemat) a-C:H coated Thermocoax 1mm

V.Philipps, EFPW Padua, Dec 2005 C o-deposit from TEXTOR tiles removed at ~0.5mm/h at 185 C (prob. higher at 130 C), but O 3 also removes underlying graphite ( EK98) Eroded surface becomes roughened & chemisorbtion forms stable C-O complexes (to >700 C) 125 C 135 C 130 C ~ 1mm EK98 ~ 40 m/h EK98 Oxidation rates of solid EK98 for 2.3% O 3 in O 2 Peaks at ~50 m/h at 130 C Decreases with burn-off Works at lower temperature but not selective for deposit ! Oxidation with Ozone H-K Hinssen et al EFDA Technology task

V.Philipps, EFPW Padua, Dec 2005 Laser treatment 20 W, λ1 μm, 10kHz, 100ns pulse duration h~50 m 1 scaning, 2s TEXTOR tile Photocleaning Flash-lamp assembly to clean JET lower divertor floor tile in active Be area, operated remotely CEA UKAEA JET horizontal divertor tile

V.Philipps, EFPW Padua, Dec 2005 ~0.5 GBq of T released in ~20ms exposure to flash-lamp from ~50cm2 of horizontal divertor tile surface analysis shows that D is released only form outer m at the surface Total T content ~5GBq still present on peak regions of this tile Results consistent with removal rate ~0.2 m/flash at 250J – lower than expected

V.Philipps, EFPW Padua, Dec Transient heat loads Special expert working group, Chairman: Alberto Loarte IPP GarchingG. Pautasso, A. Herrmann, T. Eich JET: V. Riccardo, J. Paley, P. Andrew UKAEA: G. Counsell FZJ: K.H. Finken FTU: G. Maddaluno ITER: G. Federici

V.Philipps, EFPW Padua, Dec 2005 SEWG Transient heat loads Characteristics of transient heat loads has a major impact on target design and materials Present specifications for disruptions in ITER 1. W th.que. ~ W th = 350 MJ 2. Energy quench time ~ 1 ms 3. power deposition P disr ~ 3 P s.s., toroidally uniform Best assumptions presently W t.q. ~ (0.25 ± 0.12) W th t t.q. ~ (2.3 ± 1.8) ms P disr ~ (7.5 ± 2.5) P s.s. Revision of ITER assumptions following work of EU-PWI SEWG on Disruption

V.Philipps, EFPW Padua, Dec 2005 Before the thermal quench the plasma has lost a large part of its energy Typical W t.q. /W max : 0.25 ± 0.12 for JET 0.40 ± 0.22 for ASDEX Upgrade Riccardo Pautasso JET AUG JET and AUG 4. Transient heat loads

V.Philipps, EFPW Padua, Dec 2005 power loads on divertor : confirm large broadening at the thermal quench Plasma energy at thermal quench: ~ 50% of that 20 ms earlier similar to JET and ASDEX Upgrade results G. Counsell to be published Recent work in Mast

V.Philipps, EFPW Padua, Dec 2005 Technology tasks on material damage and modelling (EU-FZK-RF) Modelling of Disruptions and ELMs Validation of ELM Damage Modelling (EU-RF) ELM-Disruption exposed Target Characterisation W and CFC damage and plasma evolution in ITER Modelling of Be damage under Disruptions/ELMs, fut.EU-RF) W and CFC under-threshold damage studies

V.Philipps, EFPW Padua, Dec 2005 PWI experiences are mainly with graphite walls in short pulse devices not enough experience on Long pulse operation T retention under ITER like material conditions Operation performance with full metallic walls Melt layer behaviour ASDEX-U tungsten first wall experiment JET ITER like wall experiment T ore Supra long pulse operation steady state plasma simulators (Magnum ) Integrated Wall material experiments

V.Philipps, EFPW Padua, Dec 2005 AUG: stepwise implementation of a full tungsten FW Objectives Erosion, deposition migration in a W/C environment Behaviour under transient heat loads Hydrogen retention behaviour Impurity seeding to replace intrinsic C radiation Development of W diagnostics Compatibility of W first wall with all relevant operation scenarios Wall material experiments: AUG

V.Philipps, EFPW Padua, Dec 2005 W Programme at AUG guard/ ICRH limiter aux. limiter hor. plate lower PSL roof baffle 2006/2007 (planned) W-coating starting with campaign 2003/ / / % 70% 85% 100% Transition to W-device W coating of lower divertor probably next year, depending on availability of technical solution (thick coating) C deposition on W rather small, but role of surface conditioning and recycling not yet completely clear Restrictions of working space identified, but remedies developed

V.Philipps, EFPW Padua, Dec 2005 New Focus on High-Z PFCs Large number of EU associations involved in characterisation of W materials, development of W coatings, W bulk target concepts and test of W as PFC CEA CaderacheW coatings, W Components, diagnostic CNR MilanoTest of high-Z PFCs ENEA FrascatiW coatings, high-Z operation, erosion/deposition/retention FZ JülichW bulk PFCs, diagnostic, high-Z operation, erosion/deposition, modeling FZ KarlsruheW materials, W components, modeling IPP GarchingW coatings, diagnostic, high-Z operation, erosion/deposition/retention, modeling IPP PragueW coatings JSI LublijanaW-H surface interaction KFKI BudapestW coatings TEKES HelsinkiW coatings, erosion VR Stockholmerosion/deposition/retention

V.Philipps, EFPW Padua, Dec MJ 20 MJ ITER JET Objectives Demonstrate low T retention Study effect of Be on W erosion Study ELMs and disruptions on wall & divertor, melt layer behaviour Develop control / mitigation techniques for ELMs and disruptions Test de-tritiation techniques Operate tokamak without C - radiation Demonstrate operation of ITER scenarios at high current and heating power with Be/W wall choice Wall material experiments: JET

V.Philipps, EFPW Padua, Dec 2005 JET with ITER like material choice Objectives Study influence of carbon chemistry Effect of Be deposition on carbon release and transport Study of Be/C(W) layers, their thermal stability, T-retention Demonstrate sufficiently low fuel retention of an ITER-like material selection to meet ITER requirements. STRATEGY: both options prepared, decide options depending on requirements Demonstrate operation of ITER scenarios at high current and heating power with Be/C/ W wall choice Integrated Wall material experiments

V.Philipps, EFPW Padua, Dec 2005 Many critical PWI issues have been addressed and significant progress achieved, inter-association collaboration & has been increased (but should be even more ) EU PWI research has benefit strongly from accompanying - EFDA technology programme, including also new partners Special Expert Working Groups have proven effective in advancing knowledge on specific issues In general, PWI research has strengthen, now in the focus of tokamak research, in particular in AUG High Z and ITER-like wall experiment in JET Concluding remarks V.Philipps, EFPW Padua, Dec 2005

EFDA- STAC decided to continue the EU PWI TF to concentrate the EU PWI programme on jointly defined important experiments in EU fusion devices Future strategy as discussed during last EU TF meeting strengthen the topical oriented work increase the objectives of existing SEWGs, new SEWG on dust improve cooperation with JET TF E and vice versa strengthen the PWI-EFDA technology programme to keep the lab work in close relation with fusion experiments Concluding remarks

V.Philipps, EFPW Padua, Dec 2005 ITER PWI Strategies: aiming for a maximum flexibility Divertor: prepare a CFC and a full tungsten divertor in parallel Decide the ITER divertor for the Tritium phase depending on transient power losses ELM& disruption control melt layer behaviour fuel retention in the H-phase [ need adequate diagnostic to detect fuel retention and material deposition rates in the H- phase] For Discussion

V.Philipps, EFPW Padua, Dec 2005 Strategies for ITER: aiming for a maximum flexibility First wall material choice: strong effort needed on characteristics of first wall PSI (steady state, ELMS.. fuel retention & removal with the present ITER materials choice (JET ITER like wall experiment) plasma behaviour with high Z walls (AUG FW W experiment) Keep (improve) the possibility to change the first wall For Discussion