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Controlled fusion based on the magnetic confinement of the plasma is one of the main aims of the Euro-fusion programme. In the fusion device, the hydrogen isotopes, in nuclear reactions, will produce helium nuclei. The products, as the ash, will be removed from the plasma in the region of the so-called divertor. Controlling the helium to hydrogen ratio in this ‘exhaust gas’ will provide information about the efficiency of the fusion process as well as of the efficiency of the helium removal system. One of the methods to perform this task is to study the properties of the discharge conducted in such exhaust gas. In this paper, the applicability of the dielectric barrier discharge (DBD) is studied. This preliminary experiment shows a great potential in applicability of this kind of discharge. The optical as well as pulse-height spectra were studied, both revealing very promising properties. In the optical spectrum, one can observe well separated hydrogen and helium spectral lines, with intensities of the same order of magnitude. Moreover, in the registered spectral region, the molecular spectra are negligible. The pulse-height spectra reveal very distinct shape in helium and hydrogen. Checking of this spectrum could provide parallel (redundant) information about the partial pressure of helium in the magnetic confinement fusion (MCF) device exhaust gas.

In this note the ratio of the second to the first order reflection is determined for the KAP and PbSt crystals, for wavelengths corresponding to the Al K-line emission. The source of the radiation was a low-voltage stabilized X-ray tube. The X-rays were detected with a Bragg spectrometer equipped with a proportional counter detector. The signal measured by the proportional counter was subsequently pulse height analyzed.

The “C/O Monitor” for Wendelstein 7-X (W7-X) is a dedicated light impurity XUV spectrometer intended to measure Lyman-α transitions of hydrogen-like ions of four low-Z impurities—boron (4.9 nm), carbon (3.4 nm), nitrogen (2.5 nm) and oxygen (1.9 nm). Since the discussed diagnostic will deliver continuous information about the line intensities, it is crucial to understand the origin of the obtained signals with respect to the experimental plasma conditions (electron temperature and density). This, however, might be difficult because of the broad acceptance angle of the spectrometer and irregular shape of the plasma edge or SOL where the radiation is expected to mostly come from, depending on the plasma temperature. For that reason, numerous analyses assuming various ranges of electron density and temperature profiles of the W7-X plasmas have been performed (assuming corona equilibrium and neglecting impurity transport processes). The aim of this work is to estimate the expected radiant flux and determine the sensitivity of the system on impurity-level changes. It will allow to improve understanding between measured signal and impurity concentration. [ABSTRACT FROM AUTHOR]

The "C/O Monitor" system for the Wendelstein 7-X (W7-X) stellarator is a dedicated spectrometer with high throughput and high time resolution (order of 1 ms) for fast monitoring of content of low-Z impurities in the plasma. The observed spectral lines are fixed to Lyman-α lines of H-like atoms of carbon (3.4 nm), oxygen (1.9 nm), nitrogen (2.5 nm), and boron (4.9 nm). The quality of the wall condition will be monitored by the measurements of oxygen being released from the walls during the experiments. The strong presence of carbon is an indication for enhanced plasma-wall interaction or overload of plasma facing components. The presence of nitrogen (together with oxygen) may indicate a possible leakage in the vacuum system, whereas the intensity of the spectral emission of boron indicates the status of the boron layer evaporated onto the wall in order to reduce the influx of heavier steel ingredients or oxygen. The spectrometer will be fixed in a nearly horizontal position and is divided into two vacuum chambers, each containing two spectral channels assigned to two impurity species. Each channel will consist of a separate dispersive element and detector. The line-of-sight of both subspectrometers will cross at the main magnetic axis. This paper presents the conceptual design of the "C/O Monitor" for W7-X which has already entered the executive stage. [ABSTRACT FROM AUTHOR]