7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Estimation of three-dimensional emissivity distribution
with multi-imaging technique
A. Sanpei1, S. Inagaki1, T. Inoue1, T. Sasaki1, Y. Ashida1, H. Fujiwara1, Y. Kawachi1 and H. Himura1
1
Department of Electronics, Kyoto Institute of Technology
e-mail (speaker): sanpei@kit.ac.jp
Three-dimensional (3D) information for plasma is
important for a wide range of plasma research fields.
Experiments and simulations have shown the importanceof helically deformed configurations and 3D modestructures in high temperature plasmas [1]. In process
plasmas, the non-uniform density of plasma would cause
non-uniform deposition on the wafer. Among the variousdevices, separated two or more detectors with computed
tomography are widely used to determine the 3D
information. However, many experimental devices arefaced with a limitation of the number of viewing ports andviewing areas. It is required that a method distinguishing
3D structure of plasma from a certain image obtained withsmall number of viewing ports. To obtain 3D structure ofplasma from limited direction, we are developing two
methods with multi-imaging techniques.
First, we have developed 3D imaging system [2] for
low temperature plasma with integral photography [3] and3D deconvolution techniques [4,5]. Developed system isconducted with multi lens and captures visible lightemitted from plasma. The system has been applied asurface wave plasma. Reconstructed distribution suggeststhat plasma emission is localized around the powered
antenna of microwave with hollow structure [6].
Estimated emission profile with double probe alsosuggests hollow structure.
Next, basis expansion technique has been applied to atorus plasma [7]. Developed system is conducted withmulti-pinhole disk and micro channel plate. Projected
intensity of soft X-ray is expressed as convolution
between emissivity and projection matrix. We apply basis
expansion with suitable orthogonal functions to emissivity.
Then, projected image is also expressed as summation ofbasis patterns. In reconstruction from obtained image, we
use the Lasso regressions. Developed system has been
applied to RFP plasmas experimentally. The experiments
have been conducted in low-aspect ratio torus RELAX[8,9]. Figure 2 shows reconstructed SXR emission profile
from experimentally obtained multi-SXR image. TheSXR emission profile with asymmetric peaks is obtained.
It suggests that the high-temperature and/or high-density
regions exist.
Detailed analysis and further applications will bediscussed.

Fig.1 Obtained reconstructed light sources overwritten on theschematic of the chamber. A hollow structure is observed [6].

Fig.2 Cross-sectional views of the 3D emission profile of SXR
calculated by using Lasso regressions. Black dashed lines
indicate the boundary of the field of view from the camera [9].

References[1] R. Lorenzini et al., Nat. Phys 5, 570 (2009).
[2] A. Sanpei et al., Opt. Express 28, 37743 (2020).
[3] G. Lippmann, C. R. Acad. Sci. 146, 446 (1908).
[4] W. H. Richardson, J. Opt. Soc. Am., 62, 55, (1972)[5] L. B. Lucy, Astron. J., 79, 745, (1974)[6] T. Ninomiya et al., JJAP 61, SI1009 (2022).
[7] S. Inagaki et al., Nucl. Instrum. Methods Phys. A1036, 166857 (2022).
[8] S. Inagaki et al., PFR 18, 1202010 (2023).
[9] S. Inagaki et al., PFR 18, 2402046 (2023).