Progress in diagnostics for characterization of plasma-wall interaction in tokamaks

1. Progress in diagnostics for characterization of plasma-wall interaction in tokamaks E. Gauthier Association Euratom - CEA Cadarache, IRFM with special thanks to C. Brosset, A. Grosman, T. Loarer, P.Monier-Garbet, R. Reichle, H. Roche, S. Rosanvallon, J.M. Travère, E. Tsitrone, X. Courtois, M. Salami, S. Vartanian, A. Murari, E. Joffrin, W. Fundamenski, A. Meigs, C. Lasnier, C. Skinner, D. Whyte, K. Itami, P. Andrew, S. Ciattaglia

2. Introduction • Diagnostics for power flux control • Infrared thermography • Diagnostics for particle control • T Retention • Dust • Erosion • Conclusion Outline

3. Motivation • ITER objectives: • 500 MW, ~steady state (400s) • Operate in a safe mode • Nuclear limit • Operational limit (safe op FPC) • Control • Power fluxes • Particle fluxes • T inventory • Dust • Erosion  Measure and control the plasma edge parameters and Plasma Wall Interactions Plasma Core Plasma Edge

4. Diagnostic route Functional specification Parameters Measurement Maintenance System Measurement specification Real Time Control Modeling Calibration Instrumentation Integration

5. Problematic of diagnostics for Power flux control • Limit power flux in steady state regime at acceptable value • Avoid Hot spots • ELMs • Disruptions • Thermocouples • Langmuir Probes • IR Thermography • IR Thermography f(x, y, z, t) ITER requirements: Divertor & first wall views T : 200 - 1000 ; 1000 - 3600°C P : 1 – 25 MW/m²; 0-5GW/m² 3 mm spatial resolution 2ms - 100 µs time resolution

6. ICRH IR Cameras LHCD Endoscope LHCD Antenna TPL Antenna View ICRH ICRH IR Cameras Limiter Views 30° Long time steady state discharge in Tore Supra IR Thermography designed for safety of PFC’s • LHCD luncher C2 • LHCD luncher C3 • ICRH antenna Q1 • ICRH antenna Q2 • ICRH antenna Q5 • TPL HR Q5A • TPL Q6B C3 Q1 Q5 Q2 C2 Q6B 7 endoscopes & IR cameras

7. 1200 25% 100% 800 T° écran Q2 (°C) 100 75 400 50 Modulation 25 P (%) 0 Q2 0 0 20 40 60 Tps (s) Real Time Control during long time discharge Monitoring of the heating of specific parts of PFC (ICRH antenna ) 950°C 1050°C P Protection 100% 25% TIR RT control of power to limit PFC heating IR JET

8. ITER-like IR Thermography diagnostic on JETNeutrons : Front end mirrors andCassegrain configuration Focussed IR image Cassegrain configuration allows extracting a visible view naturally without losses. Visible output Primary mirror Principle Secondary mirror Front mirrors Delivery R&D Fabrication Design

9. #67689, 10 kHz, 8x128, t=20ms IR and visible view imagesWide and fast visible images Wide or fast image in IR Spatial resolution: #66562, 100Hz, 408x512, t=300ms ~1 cm ~2 cm T range 200- 2500°C First time thermography in JET main chamber First account of power losses during disruptions and ELMs, first detection of filaments (R. Pitts 0-8, G. Arnoux 0-36) Similar design used for ITER (upper & equatorial views)

10. Issues on IR thermography diagnostic • Temperature Accuracy (Spatial resolution) • Divertor thermography (R. Reichle P1.40) • Measurement on metallic surface • Emissivity change Pyroreflectometry (R. Reichle P1.40) • Reflection Photothermal effect (V. Grigorova P1.93) • First mirror [A. Litnovsky] (M. Rubel O-12) • Field of view vs time resolution • x2 IR cameras

11. Diagnostics for Particle Flux control Fuel • Gas balance Safety limit • Retention Wall particles • Dust Safety & Op limit • Layers (hot dust) Safety & Op limit • Erosion monitoring Op limit • I.V.V.S. • Speckle • Confocal microscopy

12. Measurement of T inventory In vessel T limit 700g in ITER ( ~14 discharges fluence) Particle balance (T. Loarer R-3) (B. Pégourié O-21) Time resolved method Large uncertainties due to pumping speed Integrated method T retention = Injection - burn – pump recovery Small uncertainties, reduced by cumulative measurements T retention in dust and layers  local measurements Ion beam analysis [D. Whyte] Laser based methods (LID)(B. Schweer P1.38) Finj = dNp/dt + Fburn+Fpump +F in vessel

13. Dust monitoring Dust limit in ITER 1000kg in VV Hot Dust 6kg C + 6kg Be + 6 kg W Dust : size 100nm to 100µm Erosion transport dust deposition (P. Roubin O-29) Dust = particles + layers Eroded material = Dust (particles + layers)  ErosionMeasurement

14. Erosion monitoring • Vis-UV Spectroscopy Baseline ITER First wall erosion measurement influx ≠ erosion Absolute value? Disruption ? • I.V.V.S. • Speckle Interferometry • Confocal microscopy ITER needs : Erosion rate : 1-10µm/s +/-30%  : 2s Erosion range : 3 mm +/- 12µm pulse

15. Erosion monitoring In Vessel Viewing System [ENEA] Baseline ITER Amplitude modulated laser radar, scan  = 1.55 µm, f = 80 MHz  a,  • Imaging and range Accuracy ~mm • Angle 0-30° R&D needed to improve resolution Tested in laboratory conditions Vibrations ? [C. Neri]

16. ITER Divertor CCD camera Visible image Phase Image  = 1600 µm Ablation Laser 1 cm W beamsplitter mirror Altitude [µm] Shape variation Image C surface Altitude [µm] Altitude [µm] Y [cm] X [cm] X [cm] Depth crater ~ 10 to 40 µm (accuracy ~ 5µm) X [cm] Erosion measurements by means of Speckle Interferometry Shape measurements by means of Speckle Interferometry • I(1)=I0+Im cos(φ) • I(2)=I0+Im cos(φ+2π/3)=I0+Imsin(φ) • I(3)=I0+Im cos(φ+4π/3)=I0-Imcos(φ) • I(4)=I0+Im cos(φ+3π/2)=I0-Imsin(φ) • φ(x,y)=arctan ITER Mock-up Phase image CFC & W material Tunable pulsed laser

17. Speckle Interferometry at two wavelenths can provide -Shape measurements -Erosion/redeposition measurementson divertor & First wall: Localisation of Erosion/Redeposition areas  hot dust Quantitative inventory of eroded redeposited material Erosion/redeposition successfully measured in presence of vibrations Speckle Interferometry in lab fulfills ITER requirements Need to be integrated Speckle Interferometry

18. Confocal Microscopy Light source Diaphragm Beamsplitter Surface • Spatial resolution : 75 nm in z, 5 µm in x-y • Measurements on a limiter sector : • 30° of TPL : • Zones : 200 mm (radial) x 100 mm (toroidal) • Resolution 20 x 65 µm 2 optical systems :Flat surface Leading edge

19. TPL Q6a Sector Net erosion ~800µm ~1 mm Shape measurements ≠ Erosion measurements Variation of shape + ref-modeling  Erosion measurements

20. Perspectives Summary • Diagnostics in ITER are essential for operation, safety and scientific results • Diagnostic for Power flux control have already reached very good status • R&D still needed on divertor IR thermography • IR on metal (pyroreflectometry, photothermal, multi ) • Spatial resolution • First mirror • Diagnostic for Particle flux control have not been developed enough for ITER • Accurate Gas balance diagnostic is required during H phase • Diagnostics based on laser for local T measurement must be developed • Dust & layer effects are important and diagnostics are not developed enough by now • Diagnostics measuring dust formation should be implemented on today tokamaks • Erosion must be measured in Real Time for safe operation in ITER • Diagnostics for erosion measurement must urgently be developed

21. Some related contributions at this conference Dust F. Onofri, “Development of an in situ ITER dust diagnostic…” P1.80 S. Rosanvallon, “Dust limit management strategy in tokamaks…” P1.8 C. Grisolia,”From eroded material to dust:…” P1.07 P. Roubin, “Tore Supra carbon deposited layers: characterization and growth process” O-29 D. Boyle, “Electrostatic dust detector with improved sensitivity” P1.42 T inventory B. Pegourié, “Overview of the deuterium inventory campaign in Tore Supra” I-21 T. Loarer, “Fuel retention in tokamak” R-3 D. Schweer, “In-situ detection of hydrogen retention in TEXTOR by LID”P1.38 IR Thermography R. Reichle, “Concept and development of ITER divertor thermography diagnostic” P1.40 V. Grigorova, “Active Pyrometry by pulsed Photo-thermal method” P1.93 G. Arnoux, “Divertor heat load in ITER-like advanced tokamak scenarios” O-36 R. Pitts, “The impact of large ELMs on JET” O-8

22. Dust monitoring Electrostatic grids local dust deposition rate metal ? [C. Skinner] (D. Boyle P1.42) Capacitive Diaphragm microbalance local mass deposition rate [G. Counsell] scale local  global ? Light scattering density, size [DIII-D, FTU, TS…] Light extinction density, size (F. Onofri P1.80) Fast cameras (IR-vis) velocity, trajectory [NSTX] Not relevant for dust safety limit (S. Rosanvallon P1.8) IR camera qualitatif, localisation layer, hot dust Laser Induced Ablation Spectroscopy chemical composition Laser Induced Breakdown Spectroscopy chemical composition

23. Cooling loop = 120°C Active cooling : Tsurf = cte Erosion Erosion Shot 39743, 115s “Hot dust” determination from IR imaging Thick coating Thin coating Thick Coating Erosion zone : Tile surface ~ 200-300 °C Deposition zone : Thick deposits ~ 1000 °C

24. Laser Induced Spectroscopy (LIBS) LIBS retained for Mars exploration In 2010 Chemical composition of layers Quantitative ? LIBS diagnostic can be coupled with T & layers removal technics [A. Semerok]