Quiescence near the X-point of MAST measured by high speed visible imaging

Nick Walkden, James Harrison, Scott Silburn, Tom Farley, Stuart Scott Henderson, Andrew Kirk, Fulvio Militello, Andrew Thornton

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Using high speed imaging of the divertor volume, the region close to the X-point in MAST is shown to be quiescent. This is confirmed by three different analysis techniques and the quiescent X-point region (QXR) spans from the separatrix to the ψ N = 1 . 02 flux surface. Local reductions to the atomic density and effects associated with the camera viewing geometry are ruled out as causes of the QXR, leaving quiescence in the local plasma conditions as being the most likely cause. The QXR is found to be ubiquitous across a significant operational space in MAST including L-mode and H-mode discharges across maximal ranges of 9 . 8 × 10 19 m − 2 in line integrated density, 0 . 36MA in plasma current, 0 . 11T in toroidal magnetic field and 3 . 2MW in NBI power. When mapped to the divertor target the QXR occupies approximately an e-folding length of the heat-flux profile, containing ∼ 60% of the total heat flux to the target, and also shows a tendency towards higher frequency shorter lived fluctuations in the ion-saturation current. This is consistent with short- lived divertor localised filamentary structures observed further down the outer divertor leg in the camera images, and suggests a complex multi-region picture of filamentary transport in the divertor.
LanguageEnglish
JournalNuclear Fusion
DOIs
Publication statusAccepted/In press - 9 Aug 2017

Fingerprint

high speed
heat flux
cameras
causes
plasma currents
folding
tendencies
saturation
profiles
geometry
magnetic fields
ions

Keywords

  • high speed imaging
  • tokamak exhaust
  • particle transport

Cite this

Walkden, N., Harrison, J., Silburn, S., Farley, T., Henderson, S. S., Kirk, A., ... Thornton, A. (Accepted/In press). Quiescence near the X-point of MAST measured by high speed visible imaging. Nuclear Fusion. https://doi.org/10.1088/1741-4326/aa8512
Walkden, Nick ; Harrison, James ; Silburn, Scott ; Farley, Tom ; Henderson, Stuart Scott ; Kirk, Andrew ; Militello, Fulvio ; Thornton, Andrew. / Quiescence near the X-point of MAST measured by high speed visible imaging. In: Nuclear Fusion. 2017.
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abstract = "Using high speed imaging of the divertor volume, the region close to the X-point in MAST is shown to be quiescent. This is confirmed by three different analysis techniques and the quiescent X-point region (QXR) spans from the separatrix to the ψ N = 1 . 02 flux surface. Local reductions to the atomic density and effects associated with the camera viewing geometry are ruled out as causes of the QXR, leaving quiescence in the local plasma conditions as being the most likely cause. The QXR is found to be ubiquitous across a significant operational space in MAST including L-mode and H-mode discharges across maximal ranges of 9 . 8 × 10 19 m − 2 in line integrated density, 0 . 36MA in plasma current, 0 . 11T in toroidal magnetic field and 3 . 2MW in NBI power. When mapped to the divertor target the QXR occupies approximately an e-folding length of the heat-flux profile, containing ∼ 60{\%} of the total heat flux to the target, and also shows a tendency towards higher frequency shorter lived fluctuations in the ion-saturation current. This is consistent with short- lived divertor localised filamentary structures observed further down the outer divertor leg in the camera images, and suggests a complex multi-region picture of filamentary transport in the divertor.",
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Walkden, N, Harrison, J, Silburn, S, Farley, T, Henderson, SS, Kirk, A, Militello, F & Thornton, A 2017, 'Quiescence near the X-point of MAST measured by high speed visible imaging' Nuclear Fusion. https://doi.org/10.1088/1741-4326/aa8512

Quiescence near the X-point of MAST measured by high speed visible imaging. / Walkden, Nick; Harrison, James; Silburn, Scott; Farley, Tom; Henderson, Stuart Scott; Kirk, Andrew; Militello, Fulvio; Thornton, Andrew.

In: Nuclear Fusion, 09.08.2017.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Quiescence near the X-point of MAST measured by high speed visible imaging

AU - Walkden, Nick

AU - Harrison, James

AU - Silburn, Scott

AU - Farley, Tom

AU - Henderson, Stuart Scott

AU - Kirk, Andrew

AU - Militello, Fulvio

AU - Thornton, Andrew

PY - 2017/8/9

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N2 - Using high speed imaging of the divertor volume, the region close to the X-point in MAST is shown to be quiescent. This is confirmed by three different analysis techniques and the quiescent X-point region (QXR) spans from the separatrix to the ψ N = 1 . 02 flux surface. Local reductions to the atomic density and effects associated with the camera viewing geometry are ruled out as causes of the QXR, leaving quiescence in the local plasma conditions as being the most likely cause. The QXR is found to be ubiquitous across a significant operational space in MAST including L-mode and H-mode discharges across maximal ranges of 9 . 8 × 10 19 m − 2 in line integrated density, 0 . 36MA in plasma current, 0 . 11T in toroidal magnetic field and 3 . 2MW in NBI power. When mapped to the divertor target the QXR occupies approximately an e-folding length of the heat-flux profile, containing ∼ 60% of the total heat flux to the target, and also shows a tendency towards higher frequency shorter lived fluctuations in the ion-saturation current. This is consistent with short- lived divertor localised filamentary structures observed further down the outer divertor leg in the camera images, and suggests a complex multi-region picture of filamentary transport in the divertor.

AB - Using high speed imaging of the divertor volume, the region close to the X-point in MAST is shown to be quiescent. This is confirmed by three different analysis techniques and the quiescent X-point region (QXR) spans from the separatrix to the ψ N = 1 . 02 flux surface. Local reductions to the atomic density and effects associated with the camera viewing geometry are ruled out as causes of the QXR, leaving quiescence in the local plasma conditions as being the most likely cause. The QXR is found to be ubiquitous across a significant operational space in MAST including L-mode and H-mode discharges across maximal ranges of 9 . 8 × 10 19 m − 2 in line integrated density, 0 . 36MA in plasma current, 0 . 11T in toroidal magnetic field and 3 . 2MW in NBI power. When mapped to the divertor target the QXR occupies approximately an e-folding length of the heat-flux profile, containing ∼ 60% of the total heat flux to the target, and also shows a tendency towards higher frequency shorter lived fluctuations in the ion-saturation current. This is consistent with short- lived divertor localised filamentary structures observed further down the outer divertor leg in the camera images, and suggests a complex multi-region picture of filamentary transport in the divertor.

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Walkden N, Harrison J, Silburn S, Farley T, Henderson SS, Kirk A et al. Quiescence near the X-point of MAST measured by high speed visible imaging. Nuclear Fusion. 2017 Aug 9. https://doi.org/10.1088/1741-4326/aa8512