Implications of Filamentary Transport in the Divertor for Exhaust - - PowerPoint PPT Presentation

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Implications of Filamentary Transport in the Divertor for Exhaust - - PowerPoint PPT Presentation

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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

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SLIDE 1

Implications of Filamentary Transport in the Divertor for Exhaust Design

  • J. R. Harrison1, B. D. Dudson2, B. Lipschultz2, F. Militello1, A. J. Thornton1,
  • N. R. Walkden1 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

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SLIDE 2

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
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SLIDE 3

Introduction

  • 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 analytic studies [4]

  • Filaments in the PFR thought to be due to

local instabilities

MAST Outer Target JET Inner Target [1]

[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
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SLIDE 4

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 Dα 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
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SLIDE 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 5
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SLIDE 6

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
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SLIDE 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 7
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SLIDE 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

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 8
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SLIDE 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

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 9
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SLIDE 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

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 10
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SLIDE 11

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
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SLIDE 12

Filaments in the scrape-off layer

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 12
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SLIDE 13

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
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SLIDE 14

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
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SLIDE 15

Filaments in the outer leg near the separatrix

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 15
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SLIDE 16

Filaments near the Separatrix

  • Filaments are routinely observed near

the separatrix of the outer leg with different characteristics to filaments elsewhere:

  • Short-lived (≤8μs)
  • 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
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SLIDE 17

Filaments near the Separatrix

  • Filaments are routinely observed near

the separatrix of the outer leg with different characteristics to filaments elsewhere:

  • Short-lived (≤8μs)
  • 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
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SLIDE 18

Filaments near the Separatrix

  • Filaments are routinely observed near

the separatrix of the outer leg with different characteristics to filaments elsewhere:

  • Short-lived (≤8μs)
  • 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
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SLIDE 19

Filaments in the private flux region

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 19
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SLIDE 20

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
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SLIDE 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 21
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SLIDE 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 22
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SLIDE 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 23
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SLIDE 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 24
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SLIDE 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 25
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SLIDE 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 26
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SLIDE 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 27
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SLIDE 28

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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SLIDE 29

Filaments in the PFR

  • Filaments in the PFR detected using blob tracking algorithm to

determine their size

  • In the raw camera data, the filaments appear to be elliptical
  • Major radius ~ 2x minor radius
  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 29
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SLIDE 30

Filaments in the PFR

  • Filaments in the PFR detected using blob tracking algorithm to

determine their size

  • In the raw camera data, the filaments appear to be elliptical
  • Major radius ~ 2x minor radius
  • Would expect factor ~2 increase in apparent major radius from line

integration effects

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 30
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SLIDE 31

Filaments in the PFR

  • Filaments in the PFR detected using blob tracking algorithm to

determine their size

  • In the raw camera data, the filaments appear to be elliptical

− Major radius ~ 2x minor radius

  • Filaments are approximately circular, with ~1-2cm diameter (ρi ~ 1mm)
  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 31
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SLIDE 32

Filaments in the PFR

  • Toroidal mode number estimated by counting filaments
  • Region of interest (ROI) spans one toroidal period of field lines
  • Range of quasi-mode numbers, from 1-4
  • Most probable values are 2 or 3 in all cases studied
  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 32
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SLIDE 33

Filaments in the PFR

BOUT++ simulation Camera data

  • Filaments in the private flux region have been simulated with BOUT++
  • Initial 2D simulations are able to qualitatively reproduce the appearance

and propagation of these filaments – Perturbations generated by sheared flows driven by gradients in sheath potential – Radial motion due to interchange instability

1 frame = 24μs

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 33
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SLIDE 34

Outlook

  • Transport of particles and energy against field

lines in the SOL and divertor is not fully understood

  • Data from experiments indicate that the

generation of filaments occurs in regions

  • f bad field line curvature above and

below the X-point

  • Presence of instabilities local to the

divertor region could suggest this can be exploited to broaden the divertor footprint and/or the width of the PFR

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 34
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SLIDE 35

Outlook

  • The role of filaments in transporting energy in

L-mode and between ELMs in H-mode is still unclear

  • Increasing filamentary transport may

affect λne more than λTe in the divertor

  • Experiments and modelling are needed to

further understand the effects of magnetic geometry on filamentary transport and the width of the divertor footprint

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 35
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SLIDE 36

Outlook

  • The role of filaments in transporting energy in

L-mode and between ELMs in H-mode is still unclear

  • Increasing filamentary transport may

affect λne more than λTe in the divertor

  • Experiments and modelling are needed to

further understand the effects of magnetic geometry on filamentary transport and the width of the divertor footprint

  • Understanding the role of the extent of

bad curvature region below the X-point

  • Role of varying L|| and magnetic shear on

transport in the divertor

  • J. Harrison | IAEA Technical Meeting on Divertor Concepts | Vienna | 29/9/2015 | Page 36