March 26, 2008Janos Marki: ELM-induced divertor heat loads1/11 ELM-induced divertor heat loads on TCV J. Marki, R. A. Pitts and TCV Team 2008 Annual Meeting of the SPS, Geneva

March 26, 2008Janos Marki: ELM-induced divertor heat loads2/11 Outline ELMs: an introduction Experimental setup Main results Evidence of ELM filaments Summary

March 26, 2008Janos Marki: ELM-induced divertor heat loads3/11 ELMs: an introduction Best plasma confinement: H-mode configuration Increase in plasma pressure comes at a cost: Edge Localised Mode (ELM) ELM: a quasi-periodic phenomena, ejecting up to 15% of E plasma These temporary events lead to extreme heat loads on the divertors and the main chamber walls, thus reducing machine lifetimes

March 26, 2008Janos Marki: ELM-induced divertor heat loads4/11 TCV vacuum vessel Camera FOV Experimental Setup Relay optics (7 Si lenses) Detector typeCMT FPA size256 x 256 Spectral range μm Frame rate880 Hz Subframe mode25 16 x 8 Integration time1 μs -2 ms Measure IR photon flux  digital signal Apply blackbody calibration  apparent temperature Assuming   real surface temperature T Spatio-temporal evolution of T + simple model of deposited surface layer  power flux P IR (THEODOR 2D code = inverse solution of heat conduction equation)

March 26, 2008Janos Marki: ELM-induced divertor heat loads5/11 Main results Videos: 34756:First sucessful diverted shot in the 2008 campaign 33566:Discharge with type-III ELMs (ohmically heated)

March 26, 2008Janos Marki: ELM-induced divertor heat loads6/11 Main results Temperature rise during large, ECRH heated ELMs reached 500 K Expected ~20 K based on 1D semi-infinite solid heat transfer calculation The difference can be explained by very thick, thermally decoupled layers on the floor, deposited by the plasma itself and machine conditioning processes like inter-shot He glow and boronisation

March 26, 2008Janos Marki: ELM-induced divertor heat loads7/11 Results: Adding points to scaling databases Large ELMs Type-III ELMs Reactor-relevant quantities of interest: Integral energy to peak W IR and ELM rise time τ IR -> determining max. tolerable surface T

March 26, 2008Janos Marki: ELM-induced divertor heat loads8/11 Evidence of ELM filaments ELMs develop as non-axisymmetric instabilities at the outer midplane During the crash, at toroidally localised positions, filaments get ejected radially Striations at the targets – caused by ejected filaments

March 26, 2008Janos Marki: ELM-induced divertor heat loads9/11 Evidence of ELM filaments Expected divertor pattern from 1 toroidally localised filament at the midplane, as shown by magnetic field line tracing Pattern for 6 toroidally localised divertor filaments at the midplane, as shown by magnetic field line tracing

March 26, 2008Janos Marki: ELM-induced divertor heat loads10/11 Evidence of ELM filaments 1 Frame from #33948 (Full frame acq, 4.5  s integration time) For more, see presentation by R. Tye: ELM Filament Characteristics on TCV

March 26, 2008Janos Marki: ELM-induced divertor heat loads11/11 Summary Installation and commissioning of a fast IR camera has just been completed on TCV Unexpectedly high ELM temperature rises have been found (cause: layers) TCV data has been added to international empirical scaling databases Evidence for ELM filamentary nature has been found