Plasma and Fusion Research

Volume 4, 042 (2009)

Regular Articles

Divertor Impurity-Influx Monitor for ITER: Spectral Throughput Measurement on an Optical Prototype for the Upper Port and Optimization of Viewing Chords based on Computerized Tomography
Atsushi IWAMAE, Tatsuo SUGIE, Hiroaki OGAWA and Yoshinori KUSAMA
Fusion Research and Development Directorate, Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan
(Received 16 June 2009 / Accepted 14 July 2009 / Published 4 September 2009)

Abstract

We are developing a spectroscopic diagnostics system in ultraviolet and visible wavelength regions for monitoring ITER divertor plasmas. An equivalent-size prototype of the optical components for viewing upper port fanarray chords has been assembled as a system to measure spectral throughput, i.e., étendu. Collisional-radiative models for HeI and CIV are used to estimate the emission line intensities of helium ash and carbon impurity ions in a divertor region of a burning plasma. The estimated line intensity of CIV, λ772.6 nm, satisfies ITER requirements for the time resolution of measurement of Ti. A numerical simulation of the computerized tomographic technique for various pairs of viewing fan arrays has been applied to the divertor plasma region to reconstruct a two-dimensional distribution. The optimized pair of viewing fan arrays resolves a model distribution with a reasonable spatial resolution. We measure the reflectance of surfaces of carbon-fiber-composite and tungsten blocks, which make up the plasma-facing divertor target plates and the divertor dome. The reflectance of the surface of the tungsten divertor block is 23% at Hα (λ656.3 nm). A sandblast-processed tungsten surface effectively reduces direct reflectance; the resultant reflectance is less than 0.7%.

Keywords

divertor impurity-influx monitor, ITER, collisional-radiative model, computerized tomography, maximum entropy method, reflectance, tungsten, carbon-fiber-composite CFC

DOI: 10.1585/pfr.4.042

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This paper may be cited as follows:

Atsushi IWAMAE, Tatsuo SUGIE, Hiroaki OGAWA and Yoshinori KUSAMA, Plasma Fusion Res. 4, 042 (2009).