ELM-induced divertor heat loads on TCV

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

2. Outline • ELMs: an introduction • Experimental setup • Main results • Evidence of ELM filaments • Summary Janos Marki: ELM-induced divertor heat loads

3. 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 Eplasma • These temporary events lead to extreme heat loads on the divertors and the main chamber walls, thus reducing machine lifetimes Janos Marki: ELM-induced divertor heat loads

4. Experimental Setup • 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 PIR (THEODOR 2D code = inverse solution of heat conduction equation) Relay optics (7 Si lenses) TCV vacuum vessel Camera FOV Janos Marki: ELM-induced divertor heat loads

5. Main results • Videos: • 34756: First sucessful diverted shot in the 2008 campaign • 33566: Discharge with type-III ELMs (ohmically heated) Janos Marki: ELM-induced divertor heat loads

6. 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 Main results Janos Marki: ELM-induced divertor heat loads

7. Results: Adding points to scaling databases • Reactor-relevant quantities of interest: Integral energy to peak WIR and ELM rise time τIR -> determining max. tolerable surface T Large ELMs Type-III ELMs Janos Marki: ELM-induced divertor heat loads

8. 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 Janos Marki: ELM-induced divertor heat loads

9. 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 Janos Marki: ELM-induced divertor heat loads

10. 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 Janos Marki: ELM-induced divertor heat loads

11. 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 Summary Janos Marki: ELM-induced divertor heat loads