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

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 He i and C iv 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 C iv, λ772.6 nm, satisfies ITER requirements for the time resolution of measurement of T i. 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 H α (λ656.3 nm). A sandblast-processed tungsten surface effectively reduces direct reflectance; the resultant reflectance is less than 0.7%.

Hydrogen emission location, temperature and inward velocity in the peripheral helical plasma as observed with plasma polarization spectroscopy

“…The SUS tiles on the observed region were sandblasted. Sandblasting reduced direct reflection [2]. The reflectivity of carbon divertor tiles was low.…”

“…Hydrogen recycling from the peripheral plasma is an important issue for controlling fueling and pumping in a magnetic confined fusion plasma like ITER [1,2]. The core, edge, scrape-off layer (SOL) and divertor plasmas are known to exert a the strong influence on each other [3].…”

Magnetic Axial Dependency of Hα Emission Location in Peripheral Plasmas of Large Helical Device as Determined by Plasma Polarization Spectroscopy

“…For a wavelength reference, we used a Th-Ar hollow cathode lamp [13]. The inner wall of the vacuum vessel opposite the observation port was covered by stainless steel tiles, which were sandblasted to reduce direct reflection [14]. For the observation of the plasmas of R ax = 3.60 m and 4.00 m, the exposure and repetition times were 150 ms and 251.6 ms, respectively, for the plasmas of R ax = 3.70 m, 3.80 m, and 3.90 m, the exposure and repetition times were 100 ms and 201.6 ms, respectively.…”

First mirror erosion–deposition studies in JET using an ITER-like mirror test assembly

“…Good examples are the Visible and IR viewing and other spectroscopic diagnostics e.g. divertor impurity monitor and H-alpha monitor [17]. Therefore, to extend the scope of studies and to investigate the role of the opening geometry, a new experiment was performed in JET throughout the third ILW campaign (ILW-3): a specially designed, fully remote handling (RH) compatible ITER-like mirror test assembly (ILMTA) housing six mirror samples was exposed on the outside midplane main chamber wall.…”