Implications of Filamentary Transport in the Divertor for Exhaust Design J. R. Harrison 1 , B. D. Dudson 2 , B. Lipschultz 2 , F. Militello 1 , A. J. Thornton 1 , N. R. Walkden 1 and the MAST and Eurofusion MST1 teams 1 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 2 York Plasma Institute, Department of Physics, University of York, Heslington, York, YO10 5DD, UK
Introduction • Understanding transport of plasma against magnetic field lines is needed to predict power and particle loads to the first wall and divertor • This cross-field transport cannot, at present, be accurately modeled from first principles • Data from many experiments show that ‘blobs’ or ‘filaments’ play a role in cross-field transport • Greater understanding of filamentary transport can allow extrapolation to future devices with greater confidence and could be used as a means of broadening the SOL J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 2
Introduction MAST Outer Target • The presence of filaments below the x-point has been observed with probes and cameras • The experimental signatures of these filaments are typically strongest in the SOL of the outer leg and the PFR of the inner leg • These observations are supported by simulations in X-point geometry [2,3] and JET Inner Target [1] analytic studies [4] • Filaments in the PFR thought to be due to local instabilities [1] I Garcia-Cortés et al., PPCF 38 (1996) 2051-2062 [2] M. V. Umansky et al., J. Nucl. Mater 337-339 (2005) 266-270 [3] B. Dudson, PhD thesis [4] R. H. Cohen, D. D. Ryutov, Contrib. Plasma. Phys, 46 (2006) 678-684 J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 3
Filaments in the Divertor • Fluctuations within the divertor volume imaged with a high-speed camera – 120kHz time resolution, ~6mm spatial resolution – Unfiltered - detected light dominated by D α line emission – Peak signal:noise 1000:1 • Fluctuations are enhanced by subtracting a time-minimum background from the raw data [3] J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 4
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 5
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 6
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: • Filaments in the main SOL: shape distorted by magnetic shear near the X-point J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 7
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: • Filaments in the main SOL: shape distorted by magnetic shear near the X-point J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 8
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: • Filaments in the main SOL: shape distorted by magnetic shear near the X-point • Localised near the separatrix: high frequency fluctuations; small cross-field extent J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 9
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: • Filaments in the main SOL: shape distorted by magnetic shear near the X-point • Localised near the separatrix: high frequency fluctuations; small cross-field extent • Filaments in the PFR: generated in the bad curvature region of the inner divertor leg J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 10
Filaments in the Divertor • Camera data suggests there are 3 fluctuating regions in the divertor in L-mode and H-mode: • Filaments in the main SOL: shape distorted by magnetic shear near the X-point • Localised near the separatrix: high frequency fluctuations; small cross-field extent • Filaments in the PFR: generated in the bad curvature region of the inner divertor leg • This talk will give an overview of the properties of the filaments in these regions and guidance for future experiments J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 11
Filaments in the scrape-off layer J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 12
Filaments in the SOL • Filaments in the SOL can become strongly sheared in the vicinity of the X-point • The effect of shear can give the motion of the filaments a complex appearance • The filaments in the SOL in the main chamber have been well characterised in previous studies on MAST [5]: • We can check for consistency of these measurements with the divertor camera data by comparison with forward-modelled images [5] B. D. Dudson et al., Plasma Phys. Control. Fusion 50 (2008) 124012 J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 13
Filaments in the SOL We can check for consistency of these measurements with the divertor camera data by comparison with forward-modelled images • Assuming toroidal rotation only • There is qualitative agreement above and below the X-point, but modelling cannot reproduce radial motion near the X-point • Could indicate instabilities occurring locally in this region J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 14
Filaments in the outer leg near the separatrix J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 15
Filaments near the Separatrix • Filaments are routinely observed near the separatrix of the outer leg with different characteristics to filaments elsewhere: • Short-lived ( ≤ 8 μ s) • Location along the leg appears to be random • Number of filaments typically 6-12 J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 16
Filaments near the Separatrix • Filaments are routinely observed near the separatrix of the outer leg with different characteristics to filaments elsewhere: • Short-lived ( ≤ 8 μ s) • Location along the leg appears to be random • Number of filaments typically 6-12 • 1-2 cm in size J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 17
Filaments near the Separatrix • Filaments are routinely observed near the separatrix of the outer leg with different characteristics to filaments elsewhere: • Short-lived ( ≤ 8 μ s) • Location along the leg appears to be random • Number of filaments typically 6-12 • 1-2 cm in size • Space between filaments 3-6cm J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 18
Filaments in the private flux region J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 19
Filaments in the PFR Filaments appear to move poloidally along the inner leg toward the inner target, ejecting plasma deeper into the PFR J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 20
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 21
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 22
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 23
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 24
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 25
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 26
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 27
Filaments in the PFR • Filaments eject plasma deeper into the PFR • Secondary structures can form, moving radially at 0.5-1km/s J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 28
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