X-ray emission measurements following charge exchange between Ne$^{8+}$ and He.*

With a high-resolution x-ray quantum micro-calorimeter detector, x-ray emissions following single charge exchange are measured for Ne$^{8+}$ + He collisions at solar wind velocities (392 km/s to 876 km/s). To investigate the $(n,l)$ distributions of the captured electron, Balmer series line ratios are compared to ratios constructed from Multichannel Landau-Zener (MCLZ) calculations by Lyons et al. (Astrophys. J 232, 27 (2017)). Such MCLZ calculations are used to produce atomic data needed to model x-ray emissions from a variety of astrophysical objects. It is found that the measured line ratios are in excellent agreement with the calculations for the 4s $\rightarrow$ 4p emission. However, compared to the MCLZ theory, the measured line ratios indicate an increasing state-selectivity for the $4d$ and $4f$ states. Currently the apparatus is being modified to perform x-ray emission measurements for highly charged ions colliding with atomic H using the merged-beam technique.