Laboratory Measurements of Tungsten X-ray Emission for Fusion

Future burning plasma devices such as SPARC and ITER will operate in previously unexplored regions of high electron temperature, up to 30 keV. These two tokamaks (along with currently operating machines such as WEST and ASDEX-Upgrade) feature tungsten plasma facing components, which will introduce tungsten into the plasma. The conventional wisdom is that tungsten concentrations in excess of 10^-5n_e will lead to radiative collapse. It is therefore important to monitor the tungsten density and transport, which requires knowledge of wavelengths and line strengths of x-ray and EUV transitions from the multiple ionization stages, especially those between W⁶⁴⁺ and W^56+. Several measurements of x-ray and EUV emission from highly ionized tungsten have been completed (e.g., Clementson et al., 2010; Clementson et al., 2011; Beiersdorfer et al., 2012), however, gaps remain. In addition, the current calculated wavelengths are not of sufficient accuracy, as shown by Rice et al. (2021). To address this, we are using Lawrence Livermore National Laboratory's EBIT-I electron beam ion trap to produce tungsten charge states of interest and to measure the wavelengths of the appropriate X-ray and EUV emission lines. Our results are required to ensure accurate results from spectral diagnostics planned for SPARC and ITER, as well as those at other burning plasma facilities. The status of the work will be presented.