Optical boundary reconstruction of tokamak plasmas for feedback control of plasma position and shape

Abstract

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. A new diagnostic is developed to reconstruct the plasma boundary using visible wavelength images. Exploiting the plasma's edge localized and toroidally symmetric emission profile, a new coordinate transform is presented to reconstruct the plasma boundary from a poloidal view image. The plasma boundary reconstruction is implemented in MATLAB and applied to camera images of Mega-Ampere Spherical Tokamak discharges. The optically reconstructed plasma boundaries are compared to magnetic reconstructions from the offline reconstruction code EFIT, showing very good qualitative and quantitative agreement. Average errors are within 2 cm and correlation is high. In the current software implementation, plasma boundary reconstruction from a single image takes 3 ms. The applicability and system requirements of the new optical boundary reconstruction, called OFIT, for use in both feedback control of plasma position and shape and in offline reconstruction tools are discussed.

Tokamak equilibrium reconstruction code LIUQE and its real time implementation

“…Information on the flux surface shape is sometimes available from spatially resolved measurement of the plasma emissivity, typically in the soft X-ray or visible wave length ranges [18]. If this information is given as a set of points lying on the same flux surface or on a specified flux surface , the flux at these points can be evaluated using the mutual inductance formulae in Appendix A.…”

Influence of plasma diagnostics and constraints on the quality of equilibrium reconstructions on Joint European Torus

“…Since only a thin shell at the plasma edge around the last closed magnetic surface is expected to emit a significant amount of visible light, it is possible to use this emission to try to locate the position of the separatrix. Contrary to MAST, where the camera position and the plasma emission permit to reconstruct completely the separatrix, 11 JET the KL1 camera allows visualisation of only a small part of the plasma boundary. 12 As shown in Figure 6, only the plasma emission of the lower part of the plasma on the high field side is strong enough to be detected.…”

“…Therefore, the projection of the plane containing the guard limiter on the camera plane implies an almost negligible elongation of the distances on the horizontal axis direction. 11 In any case, the accuracy of the approach has been tested evaluating the position of the internal guard limiter, which appears in the frames. Since the discrepancy between the estimate of the Guard Limiter position derived from the videos and its actual coordinates (obtained from JET CATIA model) is always less than 2 cm, this can be considered the error to be associated with the developed image processing method.…”

Challenges of Video Monitoring for Phenomenological Diagnostics in Present and Future Tokamaks

“…These three algorithms have been chosen since they are identified as critical image processing needs for machine protection, as described in Table I). Concerning image stabilization, several techniques has been yet proposed to tackle this issue as in Alcator C-Mod [25] and MAST [26]. However, these techniques are either not adapted for real time computations or too brittle for noisy infrared images.…”