R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 EFDA Plasma Edge Technology Programme Monitoring of 2008 Activities Roman Zagórski European Fusion Development Agreement Close Support Unit – Garching

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 EFDA Plasma Edge Technology Programme The Programme started 5 years ago The Programme addressed various types of activities : Well defined laboratory experiments/modelling to identify/model important PWI processes in conditions relevant to ITER Analysis of samples/components exposed to tokamak plasmas (and/or in dedicated experiments) to quantify processes relevant to ITER Modelling/experiments to determine influence of ITER components specifications on their behaviour under plasma exposure (transient loads, influence on T retention and removal, etc.) Development of measurement/removal techniques for PWI-related issues which affect the licensing of ITER (Dust, Tritium) The Plasma Edge Technology Programme implemented through Art.5.1a and Art.5.1b is not supported more by New EFDA Presently, the physics part of the Programme implemented through Task Agreements - EFDA Art. 5

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 EFDA Plasma Edge Technology Programme All ITER related technology activities (tasks) moved to F4E Emerging Technologies still within EFDA (Dust, material developments, DEMO) : Transition period 10 projects left in EFDA continuation of the physics oriented Art.5.1a and 5.1b projects with the aim to close most of them by the end of 2008 (8 projects)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 Tasks in 2008 (I) Tasks finished/running/F4E in Material erosion behaviour and transport in tokamaks TW5-TPP-CARWBER, Erosion/Deposition studies of the Carbon-Beryllium-Tungsten system in PISCES-B (EU-US collaboration) TW6-TPP-CARTIL, Characterisation of erosion/redeposition balance in ITER- relevant divertor tokamaks TW6-TPP-ERDEP, Studies of material erosion and redeposition in ITER-relevant divertor target temperatures, plasma impact energies and divertor target geometries TW6-TPP-CNDMSTICK, Determination of reflection properties of hydrocarbon radicals for ITER-like divertor conditions

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 Tasks in 2008 (II) 2. Fuel retention and removal TW6-TPP-RETMIX, Characterisation of fuel retention in ITER-relevant mixed- materials TW6-TPP-GAPOX, Study of Tritium removal from macrobrush structures by oxidative methods TW6-TPP-RETMET, Determination of fuel retention in metallic materials for ITER 3. Dust production in fusion devices and removal TW6-TPP-DUSTGEN, Evaluation of dust generation mechanisms at the ITER SOL and divertor plasma TW6-TPP-DUSTMEAS, Demonstration of diagnostic techniques for time resolved dust measurements in tokamaks

R.Zagórski, PWI-TF Annual Meeting, Frascati, October Transient heat loads and control TW4-TPP-TARCAR, Characterisation of W and CFC targets exposed to ITER- relevant Type I ELM and disruption loads in plasma gun facilities (EU-RF collaboration) TW5-TPP-ITERTRAN, Modelling of ITER divertor target damage and plasma contamination following ELMs and disruptions (part. EU-RF collaboration) TW5-TPP-BEDAM, Modelling of Material Damage to Be-clad and Be-coated ITER Plasma Facing Components under Type I ELMs, Disruptions and Mitigated Disruptions and Scoping Studies for its Experimental Validation (EU-RF Be-studies contract) TW6-TPP-REPELM, Material damage for CFC and W under large cycle under- threshold ITER ELM-like loads simulated with an e-beam TW6-TPP-BECOAT, Coating of EU CFC/W targets with Beryllium for exposure to ITER-like transient loads in plasma gun facilities (EU-RF Be-studies contract) TW6-TPP-ANABE, Analysis of Be-coated and Be-clad targets for exposure to ITER-like transient loads in plasma gun facilities (EU-RF Be-studies contract) TW6-TPP-DAMTRAN, Modelling of ITER plasma facing component damage and consequences for plasma evolution following ELMs and disruptions (EU-RF Be studies contract – F4E) Tasks in 2008 (III)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October Modelling of plasma-wall interaction processes for ITER TW6-TPP-BETUNCMOD, Molecular dynamics simulations of mixed-material formation at the ITER divertor TW6-TPP-NEUTPAR, Modification of EIRENE Neutral Monte Carlo Code for Improved Computing Performance and Application to ITER Edge Plasma Modelling (Art.5.1b) TW6-TPHI-ICFCOUPL, Modeling of far SOL plasma profiles in ITER reference scenarios for optimisation of ICRH coupling calculations TW6-TPP-ERITERA, Modelling of Erosion/Redeposition for ITER Limiter Ramp up/down and Reference Scenarios including Macrobrush & Gap Geometries, Temperatures and Surface Composition TW6-TPP-ERITERB, Improvement of Surface Processes Modelling in the ERO Code for Advanced Description of mixed Material Formation in ITER Reference Scenarios TW6-TPP-SOLITER, Self-consistent modelling of plasma-wall interactions and SOL transport with real 3-D PFC geometries for ITER reference scenarios Tasks in 2008 (IV)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-ERDEP Studies of Material Erosion and Redeposition in ITER-relevant Divertor Target Temperatures, Plasma Impact Energies and Divertor Chamber Geometries Due date: 31-Dec-08 IPP, FOM_Rijnhuizen, IST Objectives To understand observed hydrocarbon erosion / co-deposition by means of dedicated experimental studies in an appropriate facility, by a detailed control of the plasma and material exposure parameters. The experimental characterisation will then be used to refine our extrapolations of the expected processes in ITER by means of complex erosion/redeposition models FOM: PILOT-PSI 1.Calibration methodology for the quantitative determination of erosion yields was investigated. 2.Explorative measurements of carbon erosion have been carried out on fine grain samples and for this material the erosion behaviour has been characterized for plasma fluxes in the range of 5 x x10 24 m -2 s The temperature effect on the carbon erosion behaviour has been investigated 4.XPS, SEM, and prolometry were performed ex situ on an exposed sample 3.Tungsten samples have been exposed to similar plasma fluxes in deuterium and analyzed ex situ with ERD, RBS, and NRA.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-CNDMSTICK Determination of Reflection Properties of Hydrocarbon Radicals for ITER-like Divertor Conditions Due date: 31-Dec-2008 OEAW, IPP-CR Objectives To determine the reflection properties of the hydrocarbon radicals expected to be formed at the ITER divertor for conditions, as close as possible, similar to those expected in ITER IPP.CR: Studies of collisions of hydrocarbon and other ions of low energies (a few up to about 50 eV) with materials relevant to plasma-wall interactions in fusion devices: carbon and tungsten (also hydrocarbon-covered steel surface). The aim was to determine the survival probability of projectile ions, dissociative and reactive processes at surfaces, and – if possible – the kinematics of collisions using the scattering method earlier developed in Prague. Some of the experiments were carried out on the special Innsbruck tandem machine BESTOF, where mass spectra can be determined with high resolution and in detailed dependence on incident energy (collision-energy resolved mass spectra, CERMS curves)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-RETMIX Characterization of Fuel Retention in ITER Relevant Mixed-Materials Status: Closed IPP, MEdC Objectives To determine the fuel retention properties of the materials which are likely to be formed in ITER as a result of the erosion and migration of material during plasma operation. In order to understand the effect of thin film coatings on hydrogen retention properties, samples were prepared with all binary film and substrate combinations of the ITER- relevant materials ( Be, W and C). BeGraphite(EK98)TVA (MEdC) BeCFC(NB31)TVA (MEdC) BeWTVA (MEdC) CWMS (IPP) CBeMS (IPP) WGraphite(EK98)MS (IPP) WCFC(NB31)MS (IPP) WBeTVA(MEdC) Samples at room temperature R.T and 400C Deuterium implantation into prepared samples was performed in the High Current Ion Source at IPP- Garching. An acceleration voltage of 0.6 keV was choosen for the ion source (corresponding to impact energy of 200 eV/D) Magnetron Sputter (MS) Thermionic Vacuum Arc (TVA)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-RETMIX The major findings: 1.In the case of C or Be coatings, D retention was predominantly determined by the film material, with almost no influence from the substrate material. 2.The D retention in W coated samples did not saturate in the accessible experimental fluence range. Total retention decreases compared to poly-crystalline bulk tungsten. 3.All CFC substrate samples showed that D retention increased continuously without saturation. The amount of D was reduced by Be or W coatings compared to that of pure CFC. 4.D retention in Be2C and Be12W similar to that in Be. 5.D retention in tungsten carbide layer was similar to that in poly-crystalline tungsten rather than graphite. No saturation was observed in < D/m 2 incident fluence range. 6.The differences of thermo-mechanical properties of mixed materials might lead to dust production. Fig. 3. D retention in (a) Be-coated, (b) C- coated and (c) W-coated samples as a function of D incident fluence.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-RETMIX A) Redeposited Be and C layers on tungsten armour at temperatures below the onset of WC carbide formation or Be12W alloy formation respectively will inhibit further D retention in the W bulk material as soon as the thickness of the layers exceeds the implantation range of incident fuel ions B) Redeposited C layers on hot tungsten armour (>1100C) will lead to formation of tungsten carbide. Such layers are not expected to have a strong influence on fuel retention in the W bulk C) W redeposition at Be or C armour can reduce D retention compared to that of the respective bulk materials with clean surfaces because diffusivity of the fuel species in W is much higher than in Be or C D) Redeposition of small amounts of C and W on the Be main chamber armour will not affect main wall fuel retention E) Redeposition of Be or W on CFC target plates will slightly decrease the fuel intake of the CFC material F) Redeposited layers forming at cool plasma facing surfaces can lead to dust formation Conclusions for ITER Operation:

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP- GAPOX Study of Tritium Removal from Macrobrush Structures by Oxidative methods Status: Closed CIEMAT Objectives: The objective of the task was to determine the efficiency of hydrocarbon removal by oxidative methods for a macro-brush geometry in ITER-like conditions. The studies have been restricted to laboratory films (hard a-C: H films (H/C ~0.4) ) produced from methane/He mixtures with thickness of nm Films have been removed by plasma etching in O2/He and N2/H2 mixtures and by thermo-oxidation at 50 mbar in O2 and N2/NO2 at several temperatures ( ºC) Gaps of 0.25, 0.4 and 1 mm width have been considered Main findings: Thermo-oxidation in O2 during 1h removes the 100 nm film only for exposure temperatures above 400ºC (upper limit for high quality films). It is expected that real Tokamak co-deposits will show a more relaxed removal conditions. Deposited samples before oxidation Samples after thermal oxidation with 50 mbar O2, during one hour, at 400ºC.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP- GAPOX Nitrogen/H2 plasmas show an erosion rate at the surface of 1/3 compared to oxygen ones. However, no cleaning effect within the gaps was observed Replacing molecular oxygen by a NO2/N2 mixture (1:1) produces higher erosion rates. At 300 ºC, the effect is similar to that of 400ºC in O2. before oxidationafter oxidation Mass spectrometry analysis of the removal process indicates that NO2 oxidation leads to formation of NO, CO and CO2, together with hydrocarbons. It is unclear how H from the films is removed (to be investigated) Plasma oxidation in an O2/He mixture removes surface films very efficiently (0.18nm/s). However, its penetration into thin gaps (0.25, 0.4 and 1mm) is very limited. An exponential decay of the erosion rates vs. depth into the gap has been found for all cases (decay length, λ, is proportional to the gap width)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-RETMET Determination of Fuel Retention in Metallic materials for ITER Due date: 31-Dec-08 MHEST, ENEA_Frascati Objectives: To determine the characteristics of fuel retention in ITER metallic materials (Be, W and Stainless Steel 316L) in conditions similar to those expected in ITER. ENEA objectives not achieved: FTU has not been working for more than one year, due to a failure in the Driver of the Poloidal System Power Supply. Presently a failure recently occurred in the control system of the Sample Introduction System is being repaired. First retention measurements on FTU possible at the beginning of Task will be closed and the work moved to future TAs MHEST part is progressing: Retention of deuterium in ITER grade stainless steel samples was studied: 24 h exposures to pure gaseous deuterium at p = 0.1 mbar and 0.01 mbar and T = 100°C, 250°C, 400 °C. High sensitivity (to distinguish H2, HD and D2) was gained after suppression of the hydrogen background by 200 hour heating of the sample at 400°C. The retained amount 6×10 16 D/cm2 was the highest at 400 °C and 0.1 mbar and proportionally less at lower deuterium pressure and temperature. Results show that an extremely high sensitivity for deuterium absorption and release can be gained with a precise pressure measuring technique.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-DUSTMEAS Demonstration of Diagnostic Techniques for Time Resolved Dust Measurement in Tokamaks Due date: 31-Jul-2008 (Delayed 31 st October) IPP, CEA, ENEA_Frascati Objectives: To investigate experimentally the performance of various proposed techniques for time-resolved measurements of dust in existing tokamaks and to evaluate their potential as a quantitative measurement technique for dust production during the various phases of the ITER discharge/operation ENEA: Dust production during FTU discharges was monitored by using the FTU Thompson scattering system Dust has been observed only after disruptions Results up to now: Only 7% of the examined discharges have not any dust following a disruption From the scattering volume and the laser repetition rate a dust density of the order of 10 7 m 3 is inferred The dust grains have diameters smaller than 1 m Experiments of controlled tungsten dust introduction have been started - a lot of events have been recorded by TS and data analysis is presently in progress Due to problems with FTU operation task will not be finished on time – moved to future TAs

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-DUSTMEAS IPP: Different diagnostics used to collect data on dust Fast Camera; IR Camera, Video Diagnostics; Dust collectors; QMB Collected data being evaluated presently. Task delayed: late start of AUG operation, damage of fast camera Rohde, et al.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-DUSTMEAS CEA contribution: Assessments of the integration of a dust injector system and electrostatic dust detector in the Tore Supra environment has been done. Dust injector system has been proposed. The system is based on the use of the dust shaker developed by MIT for Alcator-C Mod to inject about 6 mg of carbon dust of 10 μm diameter. Further design studies are still needed before construction and installation of the system. Idea based on two closely interlocking grids of conductive traces on a circuit board that are biased at V. When conductive particles land on the energized grid, a transient short circuit occurs and this current pulse can be easily detected by standard counting electronics. Isometric view of dust injector system Work has started on installation of a dust electrostatic detector (technique developed at PPPL)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-DAMTRAN Modelling of ITER Plasma Facing Component Damage and Consequences for Plasma Evolution Following ELMs and Disruptions Due date: 30-April-2009 FZK, OEAW, IPP-CR Objectives: a)To determine the material damage to the various plasma facing components and materials in ITER by the expected transient loads during ELMs, disruption thermal quenches and mitigated disruptions taking into account the detailed geometry of the PFCs and the magnetic field b) To model the evolution of the plasma after ELMs and disruptions to determine its effect on the expected damage of ITER PFCs and on the subsequent evolution of the discharge OEAW: Improvement of BIT1 code and application to the evaluation of expected power deposition profiles onto ITER PFCs during steady-state and transient loads (I)A new version of the BIT1 code has been developed. It allows simulation of multi-ion SOL including self- consistent plasma recycling and linear plasma-wall interaction models. (II)Updated BIT1 code used for ELMy-SOL simulations formulation of fit functions for describing the power and particle loads to the ITER divertors during the ELMs

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-DAMTRAN FZK: suite of codes: FOREV, MEMOS, TOKES used to analyse interactions of transients (ELMs and disruptions) with PFC CFC targets: for wide range of transient loads from 0.8 to 15 MJ/m2 and the duration of 0.5 ms vaporization is observed followed by formation of carbon plasma shield reducing heat flux to the target The main parameter of the vaporization process is the increase rate of impacting heat flux. W target: Simulations demonstrated that the total erosion (melt motion and vaporization) monotonically increases with the number of ELMs. The evaporation depth non-linearly increases with the number of ELMs The repetitive disruptions will cause significant damages of the macrobrush target. For instance after 100 disruptions of the size 15 MJ/m2 and 5 ms a deep crater about 1.5 mm and a mountain near the crater edge of 1.5 mm appear.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-DAMTRAN IPP.CR: Study of the power loads in the ITER castellated PFCs by means of kinetic calculations (PIC technique) The plasma deposition in the gaps between tiles of ITER PFCs during ELMs is strongly asymmetric. Only one side of the gap is wetted by the plasma in both PGs and TGs. In the case of PGs, the wetted side is the plasma facing side and in the case of TGs, the wetted side is the one favoured by the ExB drift. Power deposition in the gaps is made on a distance of the same order than gap widths. Increase of the power at the entrance of the gap is observed, which is due to the electric sheath, by a factor 3 minimum compared to the unperturbed perpendicular flux that falls on the tile surface. The inclination angle of the field lines plays a major role in the power deposition. It is necessary to have the smallest inclination possible to reduce the deposition Power deposition in a 2-mm gap when parallel (TG) and perpendicular (PG) to B t for 4.5 o inclination, n e = m -3, T i = 1200 eV, T e = 960 eV. Normalized power deposition in a 2-mm PG for inclination angles of 5.5 o (dash-dot line), 3.5 o (full line) and 1.2 o (dash-dot line ).

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-BETUNCMOD Molecular Dynamics Simulations of Mixed Material Formation at the ITER Divertor Due Date: 30-Sept-2008 TEKES, CEA, OEAW Objectives: To carry out molecular dynamic simulations to understand the formation of mixed materials at the ITER divertor and their interaction with hydrogen isotopes under typical conditions at the ITER divertor Potentials developed to describe BeC and BeH and WC interactions The models have been tested and are suitable for studies aimed at obtaining understanding of mixed material formation at the ITER divertor. First principle calculations of Be-W interactions have been performed to able development of a Be- W potential. Formation of Be-C alloys have been studied: Crystalline Be2C is formed from a random melt. During C irradiation of Be, Be2C layers are seen to form. Chemical sputtering, not observed in self-sputtering simulations or methods using binary collision approximation, is present in these simulations. Erosion of WC alloys due to H isotope irradiation has been studied, together with impurities (noble gases, C, and W) Preferential sputtering of C is observed; addition of noble gas impurities enhanced the C erosion. 10% addition of C to the bombarding deuterium ions resulted in a balance between C erosion and deposition. W impurities, on the other hand, lead to deposition TEKES and CEA part completed – main findings:

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPP-NEUTPAR Modification of EIRENE Neutral Monte Carlo Code for Improved Computing Performance and Application to ITER Edge Plasma Modelling Status: Closed FZJ Objectives: To parallelise the neutral modelling calculations in EIRENE in order to improve the computational performance of the coupled edge plasma modelling code B2-EIRENE for ITER modelling and to support the ITER IT in the modelling activities to be carried out as part of the design review. EIRENE module has been parallelized. The B2 module, remains seriell An interface module EIRCOP has been develop to link EIRENE to edge fluid codes ( based on MPI- technology) Full backward compatibility of the calculations with the old seriell cases has been proved For regular ITER cases the typical robust speed-up is at least a factor of 3 on 4 processors and at least a factor of 5 on 8 processors New version of code passed to ITER IT

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 TW6-TPHI-ICFCOUPL Modelling of Far SOL Plasma Profiles in ITER Reference Scenarious for Optimisation of IRRH Coupling Calculations Status: Closed ENEA_Frascati Objectives: To provide the plasma parameters across the whole SOL in ITER, up to the first wall, computed with a self-consistent model for the simultaneous interaction of the divertor and the first wall and for two of the ITER reference scenarios ( Scenario 2 (inductive Q = 10 ) and Scenario 4 (steady state Q = 5 )). Development of a coupled tool SOLPS- ASPOEL aimed at extending the model of the ITER SOL up to the first wall, i.e., including the far SOL The complete SOL model has been validated on ASDEX Upgrade data, showing good agreement with the measurements. Coupling with the EIRENE code not done Work to be continued in the frame of ITM TF WP2009.

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 Conclusions EFDA PWI Technology Programme will not be continued in the present form (Art.5.1a & b) Most ITER related activities moved to F4E Part of the program moved to Emerging Technologies (dust, T retention) Running contracts to be closed soon – 2008 (9)

R.Zagórski, PWI-TF Annual Meeting, Frascati, October 2008 Thank you for your attention