1 / 12

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

dorian-morris
Download Presentation

ELM filamentary heat load in ASDEX Upgrade

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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.

More Related