An upgraded LIBS system on linear plasma device PSI-2 for in situ diagnostics of plasma-facing materials

Abstract

Laser induced breakdown spectroscopy (LIBS) is used to detect and monitor the D and H content on the W surface due to its capability of fast direct in situ measurement in extreme environment (e.g., vacuum, magnetic field, long distance, complex geometry). A new LIBS system has been set up on the linear plasma device PSI-2 to perform in situ, real-time and remote monitoring of deuterium retention on the target surface. The new system is an upgraded version of the previous LIBS system [1] and is improved in several ways. The laser profile is improved and better focused into the chamber, the emission light collecting optics are more efficient. In addition, the timing and triggering system is updated and two different spectrometers are optimised for blue and red regime on the spectrum respectively. One of the spectrometers with Littrow configuration is dedicated to the detection of hydrogen and deuterium Balmer-alpha lines. A number of key parameters including laser energy, the (de)focusing of the laser beam, the delay time of image intensifier (MCP) are investigated and improved for the new system. The measurement by the new LIBS system is then compared to thermal desorption spectroscopy (TDS) and nuclear reaction analysis (NRA) results. The overall LIBS sensitivity and measurement accuracy are greatly improved, the time evolution of D, H content on W samples is studied before, during and after plasma-off point in the scales of seconds, minutes and hours.