Choice of the detectors for light impurities plasma studies at W7-X using 'CO Monitor' system

Highlights: • Several types of detectors for CO Monitor were considered. • Detectors ought to fulfil the sequence of requirements. • MCPs, CCD cameras, MSGC and GEM detectors were considered. • CCD camera appears to be the most suitable choice for the first operational phase OP2. -- Abstract: The 'CO Monitor' is a new spectrometer system dedicated for the continuous measurements of line intensities of carbon, oxygen, boron and nitrogen at the fusion plasma experiment Wendelstein 7-X (W7-X). Its main purpose is to deliver constant information about indicated elements with high time resolution (better than 1 ms), but low spatial resolution since the line shapes are not going to be investigated. The system consists of four independent channels, each equipped with dispersive element dedicated for measurement of selected line of interest. In order to perform the highest efficiency of the 'CO Monitor' system, it is essential to choose the proper detector type for this task. The considered options are Micro Channel Plates (MCP), Charge-Coupled Device (CCD cameras), Multi Strip Gaseous Chambers (MSGC) and the Gas Electron Multipliers (GEM) detectors. For the second Operational Phase (OP 2) of the W7-X the CCD cameras are the main candidates as a detection system for the 'CO Monitor' purpose due to their high sensitivity and the fact, that they are commercially available. Nevertheless, all other detector types are taken into account for the latter experimental operation when investigations of deuterium plasmas will start.