Basic information about impurities is obtained by studying the line emission of trace elements. Solving most problems related to impurities depends largely on understanding how their emission evolves over time and how it is distributed in space across the plasma cross-section. This makes it possible to understand how impurities affect plasma confinement and discharge scenarios. Such knowledge should enable better assessment of plasma conditions and optimization of discharge parameters in future fusion reactors.
X-ray spectroscopy used for this purpose is a well-established, effective, and powerful tool in plasma diagnostics. Measuring radiation in the 0.1 - 20 keV range is a standard method for obtaining valuable information about particle transport, magnetic configuration, and MHD (magnetohydrodynamic) phenomena. Research conducted in the Laboratory focuses on further development of plasma imaging technology in the soft X-ray (SXR) range, intended for monitoring impurity radiation in future fusion devices.
The Laboratory is also working on the development of diagnostic systems such as the Pulse Height Analyzer (PHA) and the C/O Monitor, designed to study plasma impurities in the soft X-ray and extreme ultraviolet (XUV) ranges for the Wendelstein 7-X stellarator in Greifswald, Germany.
One of the systems developed for W7-X is based on pulse height analysis using cooled semiconductor detectors operating in photon-counting mode (Pulse Height Analyzer, PHA). The purpose of this diagnostic is to measure plasma impurities in the soft X-ray range (0.1-20 keV). The device began operation on the W7-X stellarator in 2016 during the first experimental campaign.
PHA diagnostic system at the W7-X
Another device is the so-called “C/O Monitor,” designed to measure changes in the intensity of four lighter plasma impurities: boron, carbon, nitrogen, and oxygen. The spectrometer is currently under construction, and its commissioning is planned for the upcoming OP 2.0 (Operational Phase 2.0) experimental campaign in 2022.
Laboratory work on the diagnostic device “C/O Monitor” for W7-X
Research on plasma impurities is also carried out at the National Institute for Fusion Science on the Large Helical Device (Toki, Japan) (www.nifs.ac.jp/en). As part of this work, scientists from IFPiLM actively participate in experimental campaigns aimed at deepening the understanding of impurity transport in both hydrogen and deuterium plasmas. These experiments focus on studying both intrinsic impurities and those injected externally using TESPEL (Tracer Encapsulated Solid Pellet) capsules. The goal is to inject a controlled and known amount of selected impurities into the plasma and then carefully compare their behavior under different plasma conditions, such as density, temperature, heating method (ECRH, NBI), and the radial position of deposition relative to the plasma axis.
This work is carried out within the framework of the EUROfusion project.
