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ELM filamentary heat load in ASDEX Upgrade

ELM filamentary heat load in ASDEX Upgrade. A . Herrmann, A. Schmid, A. Kallenbach, ASDEX Upgrade team. Motivation Decay lengths Filament dynamics. ELM heat deposition – simplified picture. Radial movement of the filament Decelerated, accelerated, size and density dependent

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ELM filamentary heat load in ASDEX Upgrade

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  1. ELM filamentary heat load in ASDEX Upgrade A . Herrmann, A. Schmid, A. Kallenbach, ASDEX Upgrade team • Motivation • Decay lengths • Filament dynamics

  2. ELM heat deposition – simplified picture • Radial movement of the filament • Decelerated, accelerated, size and density dependent • See A. Schmid, PhD work • Energy loss by ion convection. • q|| small compared to SP values. • Do not penetrate deep into a limiter shadow. ELM Inner wall Inter ELM • Filaments are starting with pedestal (separatrix) values of ne, Te, Ti • Filament in contact to target plates (wall) looses a significant fraction of the energy on short time scales (10 μs) (near to the separatrix) • ToDo: • Follow individual filaments. • Measure the radial dynamics. • Statistics. • Model validation/falsification. ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  3. Measure the filament dynamics in the far SOL • Local measurement • Probe heads • Langmuir probes • Limiter like probes • Filament probe • Thermography • 2D Filament observation by cameras (No information on radial movement – constant shear) • Thomson scattering • Magnetic probes • SXR pedestal channel Filament probe, Reciprocating probe (LPs and thermographic heat load measurement) ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  4. Far SOL decay lengths – LPs and thermography • Comparable decay lengths for particle (Isat) and heat flux (q||). • No clear dependence on global/pedestal parameters such as Wmhd and density. • λ increases with q95 • Large (factor 5) scatter of the filament intensity. • We do not follow individual filaments! • E0 or λ variation? γTe = 100 – for this plot Position of the Filament probe: Sep_dist + 1 cm ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  5. Local measurement of filament behavior at the LFS • Magnetically driven probe (in front of the limiter), Tungsten covered, 9 LPs, • pins 6-9 radially separated for measurements of the radial propagation velocity • Pins 1-6 to measure the poloidal/toroidal velocity A. Schmid et al., RSI 78(5), 2007 ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  6. Method for vrad measurement Trace filaments over several pins -> straight line for constant/accelerated filaments -> Slope gives vrad,shape gives size (fitted, Gaussian with linear background) A. Schmid et al., submitted to PPCF Zoom -in ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  7. Filament data • Series of type-I ELMy H-mode discharges • Probe @ different separatrix positions -> changes the time of flight (the time the filament takes to reach the probe) • Manually analyzed 466 filaments Parameters: • Vrad • temporal peak width -> radial extent, Δrad • ion saturation current -> density, nfil (denotes the maximum) (using Ti=30-60eV, Te=5eV from IR/Langmuir comparison) ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  8. Lower limit on radial velocity, i.e. velocity increases with density (more dense filaments move faster) vrad ~√nfil (averaged values) velocity vs. density ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  9. Lower limit on radial velocity, i.e. velocity increases with radial extent (bigger filaments move faster) detection limit due to finite sampling rate vrad~√Δrad (averaged values) velocity vs. radial extent (radial size) ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  10. Velocity vs. distance from separatrix mean values, do not show a constant acceleration (as has been observed on MAST.) ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  11. vrad: 1.1km/s Δrad: 2.7mm (FWHM) nfil: 2.6x1018/m3 Probability distribution functions ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

  12. Summary • Typical decay length (heat, particle) are about 2-3 cm in the far SOL of AUG. • Statistics for local measurement of filament dynamics (466 filaments) • Data seems to favor the Garcia model, i.e. bigger filaments move faster. • Large scatter probably due to hidden parameters, e.g. poloidal size. • Upper limits on radial extent, line integrated density, and density gradient. • Most probable values from PDFs: vrad=1.1km/s, Δrad=2.7mm (FWHM), nfil=2.6x1018 /m3 (Δsep= 5 cm) • Radial evolution: Filament density decreases, filaments broaden with time Total particle content decreases (due to parallel losses). Values are in agreement with free parallel flow. • No constant acceleration has been found. ITPA wall&divertor, A. Kallenbach, A. Herrmann, A. Schmid et al.

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