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Farley T, Walkden NR, Militello F, Sanna M, Young J, Silburn SS, Harrison J, Kogan L, Lupelli I, Henderson SS, Kirk A, Bradley JW. Filament identification in wide-angle high speed imaging of the mega amp spherical tokamak. Rev Sci Instrum 2019; 90:093502. [PMID: 31575268 DOI: 10.1063/1.5109470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Accepted: 08/13/2019] [Indexed: 06/10/2023]
Abstract
A new tomographic inversion technique is presented for the identification of plasma filaments in wide-angle visible camera data. The technique works on the assumption that background subtracted images of filaments can be represented as a superposition of uniformly emitting magnetic equilibrium field lines. A large collection of equilibrium magnetic field lines is traced and projected onto the camera field of view and combined to form a geometry matrix describing the coordinate transformation from magnetic field aligned coordinates to image pixel coordinates. Inverting this matrix enables the reprojection of the emission in the camera images onto a field aligned basis, from which filaments are readily identifiable. The inversion is a poorly conditioned problem which is overcome using a least-squares approach with Laplacian regularization. Blobs are identified using the "watershed" algorithm and 2D Gaussians are fitted to get the positions, widths, and amplitudes of the filaments. A synthetic camera diagnostic generating images containing experimentally representative filaments is utilized to rigorously benchmark the accuracy and reliability of the technique. 74% of synthetic filaments above the detection amplitude threshold are successfully detected, with 98.8% of detected filaments being true positives. The accuracy with which filament properties and their probability density functions are recovered is discussed, along with sources of error and methods to minimize them.
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Affiliation(s)
- T Farley
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - N R Walkden
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - F Militello
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - M Sanna
- Department of Electrical and Electronic Engineering, University of Cagliari, Cagliari, Italy
| | - J Young
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - S S Silburn
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - J Harrison
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - L Kogan
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - I Lupelli
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - S S Henderson
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - A Kirk
- EURATOM/CCFE Fusion Association, Culham Science Center, Abingdon OX14 3DB, United Kingdom
| | - J W Bradley
- Department of Electrical Engineering and Electronics, The University of Liverpool, Liverpool L69 3GJ, United Kingdom
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