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

Walkden, Nick and Harrison, James and Silburn, Scott and Farley, Tom and Henderson, Stuart Scott and Kirk, Andrew and Militello, Fulvio and Thornton, Andrew (2017) Quiescence near the X-point of MAST measured by high speed visible imaging. Nuclear Fusion, 57 (12). 126028. ISSN 0029-5515 (https://doi.org/10.1088/1741-4326/aa8512)

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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.

ORCID iDs

Walkden, Nick, Harrison, James, Silburn, Scott, Farley, Tom, Henderson, Stuart Scott ORCID logoORCID: https://orcid.org/0000-0002-8205-4437, Kirk, Andrew, Militello, Fulvio and Thornton, Andrew;
  • Item type:Article
    ID code:61600
    Dates:
    Date
    Event
    25 September 2017
    Published
    9 August 2017
    Accepted
    21 June 2017
    Submitted
    Notes:© 2017 Culham Centre for Fusion Energy N.R. Walkden et al 2017 Nucl. Fusion 57 126028, DOI 10.1088/1741-4326/aa8512
    Subjects:Science > Physics > Plasma physics. Ionized gases
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:18 Aug 2017 11:00
    Last modified:11 Nov 2024 11:46
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/61600
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