Plasma and Fusion Research
Volume 14, 3402087 (2019)
Regular Articles
- 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
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
Full Text
References
- [1] L.C. Ingesson et al., Fusion Sci. Technol. 53, 528 (2008).
- [2] Y. Nagayama, J. Appl. Phys. 62, 2702 (1987).
- [3] T. Obiki et al., Plasma Phys. Control. Fusion 42, 1151 (2000).
- [4] S. Yamamoto et al., Nucl. Fusion 57, 126065 (2017).
- [5] N. Iwama et al., Appl. Phys. Lett. 54, 502 (1989).
- [6] S. Purohit et al., Rev. Sci. Instrum. 89, 10G102 (2018).
- [7] S.P. Hirshman and J.C. Whitson, Phys. Fluids 26, 3553 (1983).
- [8] N. Saito, J. Plasma Fusion Res. 92, 905 (2016).
- [9] N. Saito, Appl. Comput. Harm. Anal. 25, 68 (2008).
- [10] W.N. Van Wieringen, “Lecture notes on ridge regression”, arXiv:1509.09169 (2018).
- [11] S. Ohdachi et al., Rev. Sci. Instrum. 74, 2136 (2003).
- [12] M.W. Shafer et al., Rev. Sci. Instrum. 81, 10E534 (2010).
- [13] M.W. Shafer et al., “Observation of Multiple Helicity Mode-Resonant Locking Leading to a Disruption on DIII-D”, in proc of IAEA-FEC conf. Oct. 21-27, Ahmedabad, India, EX/P6-24.
- [14] B. Efron, J. Am. Statist. Assoc. 99, 619 (2004).