Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Report on EU-PWI SEWG on Transient Loads and Future Work Alberto Loarte European Fusion Development Agreement Close Support Unit - Garching Contributors to SEWG : CEA : F. Saint-Laurent, P. Monier-Garbet, G. Arnoux CRPP : R. Pitts ENEA : G. Maddaluno, B. Esposito IPP : G. Pautasso, A. Herrmann, T. Eich, B. Reiter, P. Lang EFDA-Garching : G. Federici, G. Strohmayer FZJ : M. Lehnen, S. Bozhenkov, J. Linke, T. Hirai FZK : I. Landman, S. Pestchanyi, B. Bazylev UKAEA : V. Riccardo, W. Fundamenski, P. Andrew G. Counsell, A. Kirk

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Outline 1. Summary of work Effects of transient loads on materials (Experiment/Modelling) Characterisation of ELM loads Characterisation of Disruption loads Disruption mitigation 2. Plans for Conclusions

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – As guideline for experiments the following energy ranges and plasma impact energies have been defined Divertor target (CFC and W without/with Be coatings) Type I ELM : 0.25 – 5 MJ/m 2, t = s, E e ~ E i ~ 3 – 5 keV Thermal quench : 3.0 – 20 MJ/m 2, t = ms, E e ~ E i ~ 3 – 5 keV Main wall (Be) Type I ELM : 0.05 – 1 MJ/m 2, t = s, E e ~ 100 eV, E i ~ 3 keV Thermal quench : 0.5 – 4 MJ/m 2, t = ms, E e ~ E i ~ 3 – 5 keV Mitigated disruptions : 0.1 – 2.0 MJ/m 2, t = ms, radiation Loads on Materials in ITER transients

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – QSPA facility provides adequate pulse durations and energy densities. It is applied for erosion measurement in conditions relevant to ITER ELMs and disruptions Plasma flow Target Diagnostic windows Vacuum chamber 60 0 The diagram of QSPA facility View of QSPA facility Plasma parameters (ELMs +Disruptions): Heat load 0.5 – 2 MJ/m 2 / 8 – 10MJ/m 2 Pulse duration0.1 – 0.6 ms Plasma stream diameter 5 cm Magnetic field0 T Ion impact energy 0.1 keV Electron temperature< 10 eV Plasma density m -3 / m -3 Conditions for ITER ELMs & disruptions not easily reproducible in tokamaks QSPA reproduces : Energy density & Timescale with plasma pressure ~ 10 too high nT 3/2 | QSPA =nT 3/2 | ITER but T| ITER = x T| QSPA TRINITI facilities QSPA

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Under ITER-like heat loads erosion of CFC was determined mainly by the erosion of PAN-fibers: 2.Noticeable mass losses of a sample took place at an energy density of 1.4 MJ/m 2 3.Severe crack formation was observed at energy densities 0.7 MJ/m 2 (cracking of pitch fibre bundles) Recommended threshold for damage 0.5 MJm -2 adopted by ITER energy density / MJm negligible erosion erosion starts at PFC corners PAN fibre erosion of flat surfaces after 100 shot significant PAN fibre erosion after 50 shots PAN fibre erosion after 10 shots CFC CFC results FZK-Pestchanyi

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Under ITER-like heat loads erosion of tungsten macrobrush was determined mainly by melt layer movement and droplets ejection: 2.Noticeable W erosion mainly due to droplet formation took place at w max = 1.6 MJ/m 2. The average erosion was approx μm/shot (1 μm/shot during the first shot, and then decreased to 0.03 μm/shot after 40th pulse). 3.Cracks formation was observed at energy densities 0.7 MJ/m 2. Metallographic sections show crack depths ranging from 50 to 500 µm. Recommended threshold for damage 0.5 MJm -2 adopted by ITER W+1%La 2 O 3 has a much lower damage threshold energy density / MJm negligible erosion melting of tile edges melting of the full tile surface (no droplet ejection) droplet ejection and bridging of tiles after 50 shots W W results

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – ELM energy loss and material effects (JET) Increase of radiation for these ELMs associated with ablation of surface layer deposits not bulk material ablation TOKES modelling of ITER plasma evolution (Landman) indicates that W ELM > 4 MJ can lead to termination fo the discharge after few ELMs (1 ELM for W ELM > 15 MJ) A. Huber/R. Pitts JET experiments at high I p ITER-like controlled ELMs of ~1MJ

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Progress in determination of divertor ELM power flux time dependence Divertor ELM power fluxes (I) more than 60% of W ELM,div arrives after q ELM,div max smaller T surf ELM W. Fundamenski AUG-Eich T.Eich JET-T. Eich

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Different scaling of IR for inner and outer divertor probably associated with energy transport processes during ELMs Divertor ELM power fluxes (II) IR ( s) ||,conv. ( s) PIBP JET- T. Eich –SEWG Meeting

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – ELM energy deposition at main chamber given by competition of parallel and perpendicular transport and filament size + detachment dynamics ELM energy fluxes to main chamber PFCs (I) JET data v ELM /c s ~ ( W ELM /W ped ) with = with of W ELM in filaments T. Eich/W. Fundamenski/R. Pitts

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – In MAST and ASDEX-Upgrade less clear correlation of W ELM with v ELM ELM energy fluxes to main chamber PFCs (II) AUG – A. Kirk MAST – A. Kirk

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Main energy flux spatial distribution linked to filament physical size which is starting to be studied in detail ELM energy fluxes to main chamber PFCs (III) A. Kirk – H-mode workshop JET – W. Fundamenski SEWG Meeting

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Pre-disruption energy confinement degradation (I) Degradation of W plasma before thermal quench studied for H-modes and L- modes (not clear size scaling in H-mode) (t.q.) (c.q.) MAST – G. Counsell

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Pre-disruption energy confinement degradation (II) Resistive-MHD caused disruption (JET-DL) Low plasma energy by the time of the thermal quench

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Pre-disruption energy confinement degradation (III) Ideal-MHD caused disruption (JET-ITB-collapse, P. Andrew EPS07) R Inner Gap Wdia 1 msec Plasma energy kept until last stages of disruption

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Pre-disruption energy confinement degradation (IV) Ideal-MHD caused disruption (H-mode VDE) W dia (MJ) D (a.u.) Plasma energy kept until last stages of VDE thermal quench Vertical drift in H-mode L-mode transition + vertical drift thermal quench

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Radiative Power during Marfes t=57.1s P wall (kW/m 2 ) Poloidal distance along wall (m) Power deposited on the Wall , t=57.1s Poloidal distance along wall (m) Radiation peaking JET (A. Huber)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Stored energy in the plasma just before thermal quench Energy loss during thermal quench/total Max. power density (conducted) ThermalMagnetic RadiatedConducted W dia [MJ]W magn [MJ]W rad [MJ] E [MJ] Q max [MWm -2 ] DLD / RLD / VDE / conducted energy on upper X-point target for lower X-point discharges JET-IR analysis by G. Arnoux : Density Limit Disruption (DLD), Radiative Limit Disruption (RLD) and Upwards Vertical Disruptive Event (VDE) Thermal Quench Energy distribution (I) Resistive-MHD disruptions consistent with large power foot broadening at thermal quench (10-50% of W dia found on upper X-point target ~ R t = 2-3 cm) VDE energy flows to upper target (broadening ?)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – W plasma lost within 2 ms No radiation correction 100% of W plasma in lower divertor Radiation correction 50% of W plasma in lower divertor & broad footprint Thermal Quench Energy distribution (II) Downwards VDE in ASDEX-Upgrade (A. Herrmann, SEWG meeting)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – #69787 During current quench the radiation distribution is poloidally asymmetric Radiation during current quench (I) JET (A. Huber)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – P wall (MW/m 2 ) Power deposited on the Wall Poloidal distance along wall (m) Radiation peaking Radiation during current quench (II) JET (A. Huber)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Massive gas injection studies in TEXTOR (M.Lehnen, S. Bozhenkov) Disruption mitigation (I) Thermal quench duration Ar mixtures: 0.5 ms He: 1 ms Current quench duration dI p /dt with increasing Ar amount

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Disruption mitigation (II) Valve installed close to the plasma in ASDEX-Upgrade (G. Pautasso) Faster effect on plasma Fastest current quench Better fuelling efficiency

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Considerable amount of carbon plasma vaporized from divertor targets can penetrate into the core in the course of disruption This carbon plasma can irradiate up to 85% of the thermonuclear plasma energy to the first wall, thus reducing the divertor heat load radiation from the core radiation from the divertor moderate disruption strong disruption Carbon plasma transport from the divertor to the core in ITER (FOREV-2D, Petschanyi) Radiation heat load to the first wall and to the divertor Disruption mitigation (III)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Disruption mitigation (V) Current quench avoidance by ECRH control of MHD growth in FTU (B. Esposito, G. Maddaluno) ECRH power injection can suppress current quench if injected close to q=2 surface, if not it slows down the process but does not prevent it

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – EC resonance Duration of disruptive phase vs ECRH power deposition radius (lithium conditioned walls: narrower current profiles) EC beam Deposition location is varied using steerable ECRH mirrors Disruption mitigation (VI)

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – SEWG Workprogramme 2008 (I) ELM transient loads Measurements of main chamber and divertor Type I ELM power and particle fluxes (AUG. MAST, JET, TCV) Optimisation of measurements of ELM fluxes by interchange of diagnostics (IR, visible cameras, etc.) among collaborating groups and by sharing of analysis techniques/software Coordinated experiments with comparable plasma conditions : dimensionless identical (pedestal parameters) Type I ELMy H-modes and */ * scans First stage of comparison of ELM models with measurements from these experiments (UKAEA, CRPP, ÖAW, CEA, IPP-CR, TEKES, IPP) Validation of 1-D and 2-D fluid and kinetic models for ELM losses along and across B with results from coordinated experiments Physics-based extrapolation of experimental/modelling results to ITER

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – SEWG Workprogramme 2008 (II) Disruption transient loads Measurements of power and particle fluxes on divertor and main chamber PFCs (including runaway fluxes) before and during the disruption for disruptions types expected in ITER (AUG. MAST, JET, TCV, TEXTOR, FTU) Optimisation of measurements of pre-disruption and disruption fluxes by interchange of diagnostics (IR, visible cameras, etc.) among collaborating groups and by sharing of analysis Coordinated experiments for disruptions expected during ITER high performance discharges : disruption in limiter plasmas, Type I ELMy H-mode disruptions (density limit, radiative limit, NTM driven and pure VDE), ideal -limit disruptions (ITBs) and low q 95 disruptions First stage of the evaluation of expected disruption fluxes in ITER for the disruption types examined Physics-based extrapolation of experimental results to ITER conditions Validation of available 2-D fluid models and modelling of ITER disruptions

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – SEWG Workprogramme 2008 (III) Mitigation of transient loads during ELMs and disruptions First attempt at joint optimisation of MGI by coordinated experiments in conditions applicable to ITER (AUG, TS, TCV, TEXTOR, JET) Coordinated experiments for mitigation of disruptions in limiter plasmas (ohmic and L-mode), and Type I ELMy H-mode. Gas injection rates and composition to be explored Quantitative comparison of effectiveness of methods for comparable plasma conditions across devices initial evaluation of size scaling and requirements for ITER First attempt to optimisation of ECRH for disruption mitigation by coordinated experiments in conditions applicable to ITER (FTU and other limiter and divertor tokamaks with ECRH) Current quench avoidance in disruptive limiter plasmas (density limit, radiative limit and ideal limits (low q95)) and disruptive diverted plasmas in Type I ELMy H-mode Evaluation of required ECRH power/current drive for comparable plasma conditions across devices initial evaluation of size scaling and requirements for ITER

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – SEWG Workprogramme 2008 (IV) Initial steps in optimisation of ELM loads controlby pellet injection by coordinated experiments in conditions applicable to ITER (AUG, JET, etc.) Coordinated experiments with comparable plasmas in Type I ELMy H-modes to determine optimum pellet characteristics as function of device size and plasma conditions minimisation of ELM energy loss and disturbance to plasma Optimise measurements of fluxes during mitigated ELMs by interchange of diagnostics (IR, visible cameras, etc.) among collaborating groups and by sharing of analysis techniques/software

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT – 10 – Conclusions Experiments and modelling of material damage under ITER-like transient loads are providing firm basis to determine maximum tolerable ELM/disruption loads for acceptable lifetime Coordinated experiments and data analysis on disruptions and ELMs are starting to provide a physics-based extrapolation of expected transient loads in ITER Further progress in 2008 expected in by coordinated experiments, better measurements and data analysis and comparison with models Systematic application of MGI and ECRH for disruptions and pellet-pacing for ELM control should provide better physics basis for ITER use in comparable conditions will allow first estimate of applicability to ITER