ELM Filament Propogation Measurements on MAST A. Kirk a, N. B. Ayed b, B. Dudson c, R. Scannel d (a) UKAEA Culham, (b) University of York, (c) University of Oxford, (d) University of Cork Presented by S. Lisgo UKAEA Culham / University of Toronto 7th ITPA D-SOL meeting Toronto Nov 6–10, 2006

INTRODUCTION Research 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/W ped, 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: T e,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) ITER

ELMS AT REDUCED PEDESTAL COLLISIONALITY Mid-plane reciprocating probe (stationary) j sat measurements – No obvious dependence of j sat, radial decay scale length, or  v r  on * ped –  t for  v r  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 LINES Full frame image (raw)

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

MAPPING FILAMENTS TO FIELD LINES Mid-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 LINES Filament propagation – Toroidal rotation goes to ~0 before filament leaves LCFS – v r 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  W ELM (assuming T i = T e )

DIVERTOR FILAMENTS ELM 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

SUMMARY Recent 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  W ped (again, assuming T i = T e ???) – 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…)