1. Slide 1 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe FZK Investigations on Wall Surfaces and Tokamak Plasma 1 Forschungszentrum Karlsruhe (FZK), Germany 2 Troitsk Institute for Innovation and Fusion Research (TRINITI), Russia 3 Kharkov Institute of Physics and Technology (KIPT), Ukraine Contents 1) Main results on expected consequences of ITER transient events Surface melting of tungsten divertor armour and beryllium first wall Evaporation and brittle destruction of carbon based materials Contamination of the SOL and core plasma after ELMs 2) Objectives Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft FUSION-PL FZK – EURATOM FUSION ASSOCIATION I. Landman 1, B. Bazylev 1, S. Pestchanyi 1 with contributions from V. Safronov 2, A. Zhitluckhin 2, V. Podkovyrov 2 and I. Garkusha 3

2. Slide 2 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Main features of FZK PWI activities Investigations are carried out for ITER, by means of numerical modelling (because available tokamaks cannot provide required transient loads) and engaging the tokamak simulators - powerful plasma guns We develop own codes to apply to ITER predictions -- behavior of fusion materials -- tolerable sizes of off-normal events Validations of the codes use mainly plasma guns and electron beams Current EFDA tasks TW3-TPP / MATDAM, TW5-TPP / ITERTRAN, TW5-TPP / BEDAM Damage to W and CFC ITER divertor materials of EU trademark (with validation by the plasma guns QSPA-T and MK-200UG) Damage to beryllium ITER first wall and Be coatings (with validation by a special plasma gun in TRINITI) Modelling of damage to ITER divertor target (after ITER disruptions and ELMs) Modelling of tokamak plasma contamination following ITER ELMs

3. Slide 3 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Transient energy fluxes expected at the ITER divertor target ITER EventRepetitionDurationTarget loadImpact energy Disruptionseldom1.. 10 ms10..30 MJ / m 2 up to 10 keV Type I ELMs1-10 Hz0.1..0.5 ms1..3 MJ / m 2 1..3 keV Normal tokamakoperation500 s10 MJ / m 2 / s1..3 keV Simulation facilities Science CentreTRINITI (RUS) and KIPT (UKR) plasma gunsFZJ (D) e-beam Facility name MK-200UGQSPAJUDITH Pulse duration [ ms ]0.050.2-0.51-10 4 Target load [ MJ/m 2 ]0.3 - 150.6 - 3010 Load spot size [ cm ]6 – 74-50.1-0.5 Magnetic field [ T ]20.5not available Impact energy [ keV ]1.5 (ions)0.2 (ions)120 (electrons)

4. Slide 4 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe FZK codes for consequences of ITER off-normal events Material surface modelling MEMOS-1.5D (fluid dynamics) Melt motion at heated metallic surface (tungsten and beryllium targets) PEGASUS-3D (thermomechanics) Brittle destruction of graphite and CFC PHEMOBRID-3D (BD threshold model) Brittle destruction of graphite and CFC Plasma modelling FOREV-2D (RMHD) Plasma shield (disruption, Type I ELM) SOL contamination (C, W, Be) Pulse transient loads at targets TOKES-2D (new MHD code) Confined plasma equilibrium Core contamination (by C so far)

5. Slide 5 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Melt motion at ITER ELM conditions Multiple ELM relevant loads at QSPA-Kh50 for EU W Deposited energy less than 1 MJ/m 2 during 0.2 ms In 2004 up to 450 shots on one W sample Damage below melting threshold is very complex: Decrease of melting threshold after many shots Violent surface cracking of bulk tungsten below melting threshold W cross-section after 1 pulse 30 MJ/m 2 0.2 ms 0.9 mm Impact energy 1.20 MJ/m 2 Absorbed energy 0.72 MJ/m 2 Pulse duration 0.2 ms after 100 pulses after 200 pulses after 250 pulses after 370 pulses after 450 pulses 1.7 mm after 450 pulses 0.5 mm

6. Slide 6 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Simulation of melt motion at ITER ELM conditions MEMOS calculates melting, resolidification and evaporation Melt motion is due to 1) p, 2) surface tension, 3) J B force Multiple ELMs and disruptions Stochastic separatrix strike positions is important: Stochastic changes of SSP affect favourably After a few thousand ELMs vaporization becomes dominant Multiple ELMs causing melting can significantly decrease the damage caused by rare disruptions (Particular figures significantly depend on the size of transient event) ITER transients Kind of damage Disruption (10 MJ/m 2, 3 ms) ELM (3 MJ/m 2 0.5 ms) W vaporization loss 1 m0.1 m W melt roughness 5-10 m1 m Single ELMs and disruptions (Simulations with Be are not yet systematic) Tungsten thresholds as functions of pulse duration The dependencies Qmelt and Qvap work well =0.3 ms + +

7. Slide 7 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Simulation of W-brushe with MEMOS Validation by QSPA-T The complicated profile of W-brushe is implemented Validation by QSPA-T is carried out The depth of W melting and resolidification profile is rather similar to that of bulk W target however melt velocity is less by a factor 0.3 - 0.5 Optimization of W macrobrush design optimization of inclination of brushes top surfaces Shadowing of brush edges may decrease melt roughness Optimal surface inclination angle / 2 Damage to the dome gaps and the divertor cassette gaps the melting of copper at the W-Cu adjoins is significant protective tungsten aprons of the gaps may be necessary

8. Slide 8 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Brittle destruction of CFC Main results from plasma guns MK-200UG and QSPA-T CFC NB31 and NS31 were exposed to 200 shots 15 MJ/m 2 Both CFC behaved similarly (regime with vapour shield) Maximum erosion rate is proportional to pulse duration PAN fibres max. erosion rate is of 20 m/ms pitch fibres max. erosion rate is of 3 m/ms (evaporation) Graphite particles of sizes of 1 to 10 2 m are collected Now investigations for EU trademark CFC at 0.5-1.5 MJ/m2 in frame of the EFDA task MATDAM started Start of vaporization: Q min =0.3 MJ/m 2 for 0.05 ms (MK-200UG) (Q min : at 0.5 ms would be Q min = 1 MJ/m 2 ) CFC surface after 150 shots at QSPA-T CFC NS31 and NB31 have been developed for ITER CFC have a 3D structure of fibres and a matrix At stationary tokamak regime CFC behaves good At the transient loads anticipated in ITER high erosion rates are discovered

9. Slide 9 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe CFC brittle destruction simulation using PHEMOBRID and PEGASUS The PEGASUS model: 3 10 6 cells of 1 m represent CFC 3D structure Thermal- and mechanical bonds between the grains Anisotropic heat transport through grain boundaries Stress due to anisotropy and temperature gradients Cracking of the bonds above elasticity threshold The crack interrupts connection between grains PEGASUS works on microscopic scale (weeks of running) PHEMOBRID works on macroscopic scale (BD threshold of CFC (10 KJ/g) is like melting point of W) (PHEMOBRID: 3D code also but only a few hours of running) PHEMOBRID results Simulation: 0.8 MJ/m 2 0.5 ms Experiment 0.3 MJ/m 2 0.05 ms (data for the emissivity 0.9) Value of thermal conductivity is important Pulse shape is also important ( and 50%)

10. Slide 10 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe PEGASUS: BD damage to a standard CFC structure PEGASUS: BD damage to improved CFC structure New CFC structure is suggested The PAN fibres are inclined under 45 deg to the pitch fibres In PEGASUS simulations BD erosion rate has decreased significantly (~ 5 times) Experiments at MK-200 UG to proof this qualitative prediction are set up (the CFC is to be cut as [111]) The CFC erosion is due to preferential cracking on the surfaces of PAN fibres erosion depth 30 um, 4000 K at the boundary This simulation only tried to discover BD erosion features but not the scale Validation is necessary CFC simulations using PEGASUS

11. Slide 11 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Development of FOREV-2D magnetic toroidal geometry of ITER and JET are available multi-fluid SOL plasma description (ions of D, T, He, C) radiation transport in toroidal geometry for C is implemented Results obtained with upgraded FOREV-2D radiation load of the first walls in ITER and JET a rough validation by JET was carried out (20 versus 35 MW) SOL contamination by carbon impurity after Type I ITER ELMs For Q 1 MJ/m 2, carbon ions fill SOL for several ms The density up to 10 21 m 3, thus DT is dissolved in C In few ms SOL is cooled down to a few eV by radiation losses. Influx of carbon impurity into the pedestal after ELM: 3 10 17 m -2 Modelling of ELM-induced SOL contamination

12. Slide 12 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Contamination of ITER core after ELMS (first simulations with the new code TOKES) Main Features of TOKES The Grad-Shafranov equation is solved at each time step (2D magnetic field evolves together with plasma) Multi-fluid plasma, Pfirsch-Schlüter cross transport so far (now D, T, He and C ion species are available) Poloidal field coils automatically control plasma boundary D- and T beams heat and feed, radiation cools D+T He + n reaction produces burning by alphas First preliminary result Whole ITER confinement of 500 s was simulated Tolerable ELM size 1 MJ/m 2 for ELM frequency 0.5 Hz Rather uncertain implications have still been used: (plasma fraction dumped out in ELM burst assumed 0.5) We see that ELMs do not clean the plasma of impurities Carbon impurity propagation into the core after ELM (TOKES)

13. Slide 13 17-19 Oct 2005, EFDA PWI meeting, CEA CadaracheI.S. Landman, FZ-Karlsruhe Objectives Up to now mainly carbon transport in SOL was simulated (W and Be not) Therefore we will develop tungsten impurity transport in SOL and the core Radiation transport also for tungsten impurity Further material investigations (CFC, W, Be) with PEGASUS and MEMOS in particular, aiming impurity influxes into SOL Main future activities are going to be devoted for ITER transients Further quantification of the heat fluxes to ITER divertor and first Quantification of ELM size threshold for radiation collapse caused by the impurities Lifetime prediction for CFC, W and Be Theoretical support of ongoing experiments with EU materials for ITER Continue W-O-H chemical erosion with MD code CADAC