Plasma and Fusion Research

Volume 14, 3402087 (2019)

Regular Articles

Tomographic Inversion Technique Using Orthogonal Basis Patterns
Satoshi OHDACHI1,2), Satoshi YAMAMOTO3), Yasuhiro SUZUKI1,2), Shishir PUROHIT2) and Naofumi IWAMA1)
1)
National Institute for Fusion Science, Toki 509-5292, Japan
2)
SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan
3)
Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
(Received 17 January 2019 / Accepted 18 March 2019 / Published 3 June 2019)

Abstract

Tomographic reconstruction of the emission profile is a typical ill-posed inversion problem. It becomes troublesome in fusion plasma diagnostics because the possible location/direction of the observation is quite limited. In order to overcome the difficulty, many techniques have been developed. Among them, series expansion methods are based on decomposing the emission profile with orthogonal or nearly orthogonal basis patterns. Since it is possible to ignore the surplus components with higher spatial frequency, this type of method is robust against noise issues. Two topics are discussed in this article. The first issue is the comparison of the basis systems themselves. Conventional one of Fourier-Bessel and a new one of the so-called Laplacian eigen function are compared from the viewpoint of the capability of expressing the patterns that appear in the fusion plasma experiment. The second issue is the application to the tangential viewing imaging system. It is shown that, even from the limited information, tomographic reconstruction can be adequately performed with appropriate use of the regularization, especially with the use of the L1 regularization.

Keywords

tomography, Heliotron-J, orthogonal, series expansion

DOI: 10.1585/pfr.14.3402087

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