Design, construction, and performance of a composite mirror for collecting Thomson scattered light from the large helical device plasma

K Narihara,H Hayashi,K Yamauchi,I Yamada

doi:10.1063/1.1787919

K Narihara, H Hayashi + Show 2 more

Open Access

https://doi.org/10.1063/1.1787919

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Abstract

A 1.5 m×1.8 m rectangular composite mirror composed of 138 segment hexagonal spherical mirrors was constructed for collecting Thomson scattered light from the Large Helical Device plasma. The hexagonal mirrors with side length of 87 mm were patched on the surface of a framework made of glass fiber reinforced plastic. The position and angular orientation of each mirror are adjusted with three pairs of push-and-pull screws attached to the back plane of the mirrors so that the image of a tiny light source (0.1 mm in diameter) formed by each segment mirror be minimized and coincide with each other on a charge coupled device plate. The optical quality and its long-term stability of the assembled mirror have been monitored and sufficient for the present purpose.

Highlights

Incoherent Thomson scattering (TS) of intense laser off plasma electrons is a well-established method to measure the electron temperature 共Te兲 and density 共ne兲 in the contemporary fusion plasma experiment
We designed a TS system which adopts a large rectangular view window of 0.33 m ⫻ 0.58 m in the effective area and a large mirror 共1.5 m ⫻ 1.8 m兲 as a light collecting optic for the Large Helical Device (LHD)
We describe the design, assembly, and performance of this composite mirror

Summary

INTRODUCTION

Incoherent Thomson scattering (TS) of intense laser off plasma electrons is a well-established method to measure the electron temperature 共Te兲 and density 共ne兲 in the contemporary fusion plasma experiment. In order to obtain scattering signals intense enough to reduce Te and ne accurately, we must prepare a very intense laser, bright optics, and highly efficient detectors. We designed a TS system which adopts a large rectangular view window of 0.33 m ⫻ 0.58 m in the effective area and a large mirror 共1.5 m ⫻ 1.8 m兲 as a light collecting optic for the Large Helical Device (LHD).. It is not easy to fabricate a mirror of this size and shape as one body; even if it is possible it would be very expensive. To alleviate this technical difficulty we adopted a composite mirror composed of many segment mirrors patched on a framework of the desired size and shape. We describe the design, assembly, and performance of this composite mirror

DESIGN CONSIDERATIONS

ASSEMBLING AND ADJUSTMENT

Findings

PERFORMANCE AND DISCUSSION