ELM Filament Propogation MeasurementsELM Filament Propogation Measurementson MASTon MAST

A. Kirka, N. B. Ayedb, B. Dudsonc, R. Scanneld(a) UKAEA Culham, (b) University of York, (c) University of Oxford, (d) University of Cork

Presented by S. LisgoUKAEA Culham / University of Toronto

7th ITPA D-SOL meeting Toronto Nov 6–10, 2006

INTRODUCTIONResearch summary

– ELM story– MHD trigger (peeling / ballooning mode, …)– pedestal transport– filament formation ,separation from the pedestal, propagation through the SOL

– Currently, trying to understand filament transport characteristics– toroidal mode number– toroidal / radial velocities

– fraction of the pedestal energy lost during an ELM,W/Wped, that is carried by filaments after separation

– Principal diagnostics– Photron fast camera (up to 250,000 Hz, 1+ s integration time)– outer mid-plane reciprocating probe (fast Langmuir triple probe + magnetics)– outer mid-plane edge Thomson scattering system (4 lasers, 1+ s between pulses)

– Recent results reported on here– ELM’s generated at substantially lower *ped than reported previously

– filament field-line mapping at high Photron frame rates (100,000 Hz) – observations of ELM filaments in the outer divertor

ELMS AT REDUCED PEDESTAL COLLISIONALITY

First observations from MAST low *ped H-mode

– New “record” for MAST: Te,ped = 435 20 eV

– scenario: immediately after boronization, tailored fuelling, increased beam power (2.5 MW)– (previously, MAST data differentiated by low aspect ratio and high pedestal collisionality)

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ELMS AT REDUCED PEDESTAL COLLISIONALITY

Mid-plane reciprocating probe (stationary) jsat measurements

– No obvious dependence of jsat, radial decay scale length, or vr on *ped

– t for vr based on D signal, i.e. single “start time” for all filaments associated with a particular ELM– preliminary data, only ~5 shots

MAPPING FILAMENTS TO FIELD LINESFull frame image (raw)

MAPPING FILAMENTS TO FIELD LINESFull frame image (raw)

– Filaments are aligned to magnetic field lines– EFIT error is assumed to be systematic

MAPPING FILAMENTS TO FIELD LINESMid-plane images

– Reduce window size to increase frame rate, follow filament movement– 100 kHz– (mapping a bit of an “art” with smaller window size)– radial position within 2 cm (maybe better), toroidal position to 1 degree– no filamentary structures observed inside LCFS (yet, will try with HeII filter)

MAPPING FILAMENTS TO FIELD LINESFilament propagation

– Toroidal rotation goes to ~0 before filament leaves LCFS

– vr goes from 0 at LCFS to 1–3 km s-1

– Filaments leave LCFS at different times

ENERGY CONTENT OF FILAMENTS (ELECTRONS ONLY)Characterization of filament plasma with Thomson scattering

– High resolution edge TS shows separation from pedestal– outer mid-plane measurement– 5 s between laser pulses– (recall: filament stopped rotating before leaving LCFS, and prior, only rotates ~ ??? cm toroidally before leaving LCFS, significantly less than 5–10 cm characteristic filament toroidal extent)

– Generally, each filament contains 2.5% of WELM (assuming Ti = Te)

DIVERTOR FILAMENTSELM filament imaging in the outer divertor

DIVERTOR FILAMENTSELM filament imaging in the outer divertor

– Spiral pattern away from strike-point– the “wall” on most devices – non-rotating filaments generate spiral pattern due to radial q shear– target radial “footprint” may not be representative of upstream radial size

SUMMARYRecent results and future plans

– Filament propagation on MAST appears to be independent of *ped

– (preliminary results only!)

– Filaments do not all leave the LCFS at the same time

– Each filament carries 2.5% of Wped (again, assuming Ti = Te ???)

– Re-work camera optics to get larger field-of-view into a smaller window, improving accuracy of field line mapping at high frame rates

– Filter for HeII light, which radiates in the pedestal on MAST (may not be bright enough, even with additional seeding we’ll see…)