Bradley, JW
(2019)
Filament identification in wide-angle high speed imaging of the mega amp spherical tokamak.
Review of Scientific Instruments, 90 (9).
093502-.
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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.
| Item Type: | Article |
|---|---|
| Depositing User: | Symplectic Admin |
| Date Deposited: | 17 Sep 2019 09:49 |
| Last Modified: | 19 Jan 2023 00:26 |
| DOI: | 10.1063/1.5109470 |
| Related URLs: | |
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3054937 |
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