1. Institute for Plasma Physics Rijnhuizen Heat load asymmetries in MAST G. De Temmerman a,b, A. Kirk a, E, Nardon a, P. Tamain a, A. Thornton a a Present address: FOM Institute for Plasma Physics Rijnhuizen, Ass. EURATOM FOM, Nieuwegein, NL d EURATOM/UKAEA Fusion association, Culham Science Centre, Abingdon, OX14 3DB

2. G. De Temmerman Annual meeting of the SEWG on transient heat loads MWIR camera (SBFP, USA): 320 x 256 pixel @ 300Hz up to 10kHz for 128 x 8 pixel window Range of lenses (5-50mm), 5mm typical resolution 2.5-5 µm LWIR camera (Thermosensorik, D): 256 x 256 pixel @ 880Hz up to 20kHz for 128 x 8 pixel window (up to 25 kHz) 2 lenses (15-25mm), 7mm typical resolution 7.6-9 µm 2 Hardware

3. G. De Temmerman Annual meeting of the SEWG on transient heat loads 2 types of views mainly available (with standard lenses): LWIR camera view 4, 15 mm lens MWIR camera view 4, 13mm lens MWIR LWIR Spatial resolution: 7mm for LWIR, 5mm for MWIR Used for dust transport studies Zoomed views possible Available for upper and lower divertor 3 Available views (1/3)

4. G. De Temmerman Annual meeting of the SEWG on transient heat loads LWIR MWIR 2 types of views mainly available (with standard lenses): LWIR camera view 1, 15 mm lens MWIR camera view 1, 13mm lens Spatial resolution: 7mm for LWIR, 5mm for MWIR 4 strike points observed simultaneously 14.5kHz max for LWIR 6kHz max for MWIR 4 Available views (2/3)

5. G. De Temmerman Annual meeting of the SEWG on transient heat loads Wide angle view (7mm lens, midplane) Views around 70% of the vessel Ideal for disruption studies E. Delchambre et al, Images taken during a disruption (1 frame every 3.2ms) Available views (3/3)

6. G. De Temmerman Annual meeting of the SEWG on transient heat loads Outline LWIR/MWIR imaging and heat flux calculations Status of the MAST DMV Heat flux profiles during ELM control experiments Heat load asymmetries during L-mode discharges Heat load asymmetries during H-mode discharges

7. G. De Temmerman Annual meeting of the SEWG on transient heat loads Combined LWIR/MWIR imaging Over-estimation of temperature at 5 m compared to 8 m: 30-40% Attempt of modelling the effect of hot spots on temperature measurements (E. Delchambre, PFMC12 conference): bulk substrate covered with dust in radiative equilibrium (given coverage) 2 temperature distribution 7 MAST case can be reproduced using different assumptions on dust coverage and size (at least for the lower divertor) Difference between upper and lower divertor (under investigation) Future work: LWIR/MWIR measurements on carbon and tungsten at different base temperatures

8. G. De Temmerman Annual meeting of the SEWG on transient heat loads Heat flux calculations 3-5 µm toroïdal symmetry Use of temperature profile along a tile (see red line) 2D hypothesis linear calculation Thermal quadrupoles approach [JL. Gardarein, International Journal of Thermal Sciences, 48 (2009) 1-13] What has been done : code development and preliminary tests with experimental data. [ J.L. Gardarein] Future works: - test with numerical data (inverse calcul. should give input exp. data) - C++ development SWEEPING OF THE STRIKE POINT

9. G. De Temmerman Annual meeting of the SEWG on transient heat loads LWIR/MWIR imaging and heat flux calculations Status of the MAST DMV Heat flux profiles during ELM control experiments Heat load asymmetries during L-mode discharges Heat load asymmetries during H-mode discharges

10. G. De Temmerman Annual meeting of the SEWG on transient heat loads MAST DMV: design and status Disruptions can be mitigated via the injection of large quantities (~ 10 21 particles) of impurity gas Mitigation decreases heat loads by radiating away stored energy prior to thermal quench Fast acting valve used to inject gas Noble gases used for impurity species Disruption mitigation valve on MAST - Supplied by FZJ - To be operational by the end of September - Located on HM12, centre left port - Gas injected along a pipe to deliver impurities to 30 cm from the plasma edge - Installed on the machine, final commissioning in next few weeks BOLOMETER VIEWS Valve To vessel

11. G. De Temmerman Annual meeting of the SEWG on transient heat loads DMV: plans for end 2009 Experimental proposals Physics studies only initially – no active mitigation of disruptions via prediction Disruption mitigation experiments for M7c and continuing to M8 Study the effect of mitigation on target heat loads using upper and lower divertor IR cameras Observe the evolution and penetration of the injected impurities using fast cameras Coverage of DMV from two opposite sectors with high speed cameras Assess the effect of an edge transport barrier on disruption mitigation Dependence of mitigation timescales on q=2 surface location Mitigation of plasmas at high beta

12. G. De Temmerman Annual meeting of the SEWG on transient heat loads LWIR/MWIR imaging and heat flux calculations Status of the MAST DMV Heat flux profiles during ELM control experiments Heat load asymmetries during L-mode discharges Heat load asymmetries during H-mode discharges

13. G. De Temmerman Annual meeting of the SEWG on transient heat loads φ R Deepest radius reached by FL: (Ψ pol 1/2 ) min φ R (m) Heat flux during ELM control experiments Strike point splitting observed by IR in outer divertor Vacuum modelling predicts splitting Spiralling structure exists despite stochasticity Good match between heat flux profile and calculated field lines radial penetration

14. G. De Temmerman Annual meeting of the SEWG on transient heat loads LWIR/MWIR imaging and heat flux calculations Status of the MAST DMV Heat flux profiles during ELM control experiments Heat load asymmetries during L-mode discharges Heat load asymmetries during H-mode discharges

15. G. De Temmerman Annual meeting of the SEWG on transient heat loads LWIR MWIR Camera views for routine observation of all 4 strike-points – high-speed region-of-interest imaging (vertical) – building database for studying heat load asymmetries (in/out and up/down) for a wide range of plasma scenarios Power balance in L-mode discharges 15 In L-mode, all the energy coming to the SOL goes in the divertors (no close fitting wall in MAST) 15 Heat load asymmetries in L-mode

16. G. De Temmerman Annual meeting of the SEWG on transient heat loads LOWER SINGLE NULL UPPER SINGLE NULL FRACTION OF UP/DOWN ENERGY VERSUS SEPARATION BETWEEN PRIMARY AND SECONDARY SEPARATRICES FRACTION OF IN/OUT ENERGY VERSUS SEPARATION BETWEEN PRIMARY AND SECONDARY SEPARATRICES L-mode: Asymmetries depend on magnetic configuration Non-symmetric behavior of in/out asymmetries Heat load asymmetries in L-mode

17. G. De Temmerman Annual meeting of the SEWG on transient heat loads Heat load asymmetries in L-mode Evolution of q with magnetic geometry Change of heat flux profile with magnetic geometry Up/down asymmetry: q upper > q lower q decreases in SND with input power

18. G. De Temmerman Annual meeting of the SEWG on transient heat loads Comparison IR data at target and probe measurements at midplane Gundestrop probe Heat load asymmetries in L-mode q asymmetric behaviour also observed at midplane Large scatter for different pins in DND configuration, not clear why ?

19. G. De Temmerman Annual meeting of the SEWG on transient heat loads q scaling in L-mode: 1 st attempt Dataset: 70 DND L-mode discharges NBI power: 0 to 3.5MW Previous scaling (Ahn et al) gave similar power dependence

20. G. De Temmerman Annual meeting of the SEWG on transient heat loads LWIR/MWIR imaging and heat flux calculations Status of the MAST DMV Heat flux profiles during ELM control experiments Heat load asymmetries during L-mode discharges Heat load asymmetries during H-mode discharges

21. G. De Temmerman Annual meeting of the SEWG on transient heat loads 500 Hz 70us integration time Heat flux profiles during ELMs Experimental setup: LWIR camera: 13.5kHz, upper divertor MWIR camera: 5.6kHz, lower divertor DND discharges Up/down, in/out asymetries Heat flux profiles Power balance

22. G. De Temmerman Annual meeting of the SEWG on transient heat loads Heat flux profiles during ELMs Evolution of heat flux profiles during an ELM (1 frame every 72 s): Inner divertorOuter divertor Filamentary structure clearly observed in outer divertor Heat flux profile in inner divertor only slightly modified during an ELM

23. G. De Temmerman Annual meeting of the SEWG on transient heat loads Energy balance during ELMs Comparison between ELM energy from EFIT and IR Within uncertainties, power balance seems achieved during ELMs

24. G. De Temmerman Annual meeting of the SEWG on transient heat loads Ratio of energy to upper and lower divertors Heat load asymmetries during ELMs Ratio of energy to outer and inner divertors E outer is between 15 and 40 times higher than E inner E upper is between 1.5 and 2.5 times higher than E lower

25. G. De Temmerman Annual meeting of the SEWG on transient heat loads Future plans LWIR/MWIR measurements on tungsten and carbon at elevated temperatures Heat load asymmetry study during SND shots Use both IR cameras for maximum time resolution (10 and 20kHz) Study of surface layer effect on inner and outer divertor Effect of ELM coils on heat fluxes during H-mode (hopefully) Heat load studies during DMV experiments