Estimation of Photon Flux of the Oxygen Lyman-α Line Emitted from the W7-X Plasmas.

The low-Z impurities of the magnetic confined fusion plasmas can provide important information about the wall condition and plasma--wall interactions. In order to accomplish this aim, a special spectrometer called "C/O Monitor" was designed for the W7-X experiment. This system is dedicated to measure Lyman-α transitions of four low-Z impurities: carbon (3.4 nm), oxygen (1.9 nm), nitrogen (2.5 nm) and boron (4.9 nm). It is a high throughput and high time resolution spectrometer which allows to measure the line intensities evolution of indicated elements including information of the background (continuum). The designed spectrometer consists of two vacuum chambers positioned nearly horizontally -- each chamber containing two dispersive elements. Their lines of sight cross at the main magnetic axis of the W7-X plasma. The spectrometer's installation is planned prior to the next Operational Phase (OP 2) which is to be performed in 2021. The "C/O Monitor" system has entered the executive stage. In the "C/O Monitor" diagnostic system, it is important to determine the incoming photon flux and to estimate the detector's response and the topmost time resolution. Moreover, this might be relevant for a quantitative interpretation of the experimental data as well as for an attempt at the calibration of this system. As a consequence, the incoming photon flux from the Lyman-α transitions of selected ions should be analyzed. In this paper, the estimation of the photon flux of the oxygen Lyman-α line and the whole methodology are described. [ABSTRACT FROM AUTHOR]