Diagnostics for molybdenum and tungsten erosion and transport in NSTX-U

Abstract

A comprehensive set of spectroscopic diagnostics is planned in the National Spherical Torus Experiment Upgrade to connect measurements of molybdenum and tungsten divertor sources to scrape-off layer (SOL) and core impurity transport, supporting the installation of high-Z plasma facing components which is scheduled to begin with a row of molybdenum tiles. Imaging with narrow-bandpass interference filters and high-resolution spectroscopy will be coupled to estimate divertor impurity influxes. Vacuum ultraviolet and extreme ultraviolet spectrometers will allow connecting high-Z sources to SOL transport and core impurity content. The high-Z diagnostics suite complements the existing measurements for low-Z impurities (carbon and lithium), critical for the characterization of sputtering of high-Z materials.

Relativistic R -matrix calculations for the electron-impact excitation of neutral molybdenum

“…Furthermore, NSTX-U has plans to install a limited set of molybdenum tiles, with the potential * rsmyth41@qub.ac.uk to upgrade to a fully high-Z wall [10]. However, a major disadvantage of using high-Z atoms such as molybdenum (Z = 42) lies in the fact that they have the potential to greatly hinder the performance of the tokamak, arising due to an influx of impurities from the PFCs into the fusion plasma core.…”

Electron-impact ionization of the Si atom

“…Plasma facing components (PFCs) that can withstand high heat loads, have low sputtering rates [1], and low tritium retention rates [2] are of keen interest on current and next generation magnetically confined fusion experiments [3,4]. The next generation of tokamak experiments [5] and most existing devices use either tungsten [6] or molybdenum [7] as a PFC. One of the concerns with such heavy elements being used as a PFC is the potential for large radiative losses if the material is sputtered and transports into the core plasma, leading to a possible quenching of the fusion reaction [8].…”