Presentation #108.16 in the session “Missions and Instruments (Poster)”.
Non-equilibrium plasmas are plasmas that are either underionized or overionized relative to the electron temperature, and thus are dominated by radiative recombination or collisional ionization, respectively. They are important for a variety of transient X-ray sources such as supernova remnants (SNR), solar flares, and cluster shocks. In many of these sources, the details of the cooling/heating mechanisms that lead to the presence of a recombining/ionizing plasma are not yet well understood. To characterize these plasmas and study their formation, accurate non-equilibrium ionization (NEI) plasma models are necessary. Already CCD-resolution observations of the brightest recombining SNR show that current NEI models, while largely agreeing with each other at low spectral resolution, under-predict the observed line emission of K-shell transitions from n>3 in He-like ions — these transitions are populated by recombination cascades and constitute an important temperature diagnostic. Additionally, at high spectral resolution, direct comparisons between different NEI models show larger deviations between the model spectra than is the case for different CIE models. Benchmarks in a controlled laboratory environment provide the means to assess and ensure the accuracy of these models. Using the Lawrence Livermore National Laboratory’s EBIT-I electron beam ion trap and the ECS high-resolution calorimeter spectrometer built at NASA/GSFC, we conduct high-accuracy measurements of X-ray line emission from highly charged ions of astrophysically relevant elements in non-equilibrium plasmas. Specifically, we utilize the EBIT Maxwellian simulator to create and study ionizing and recombining plasmas as a function of Maxwellian electron temperature, to compare to available NEI models. These data will help to interpret existing observations of a variety of transient sources, and are particularly important for interpretation of new high-resolution observations by the calorimeter instruments to be flown on the X-ray Imaging and Spectroscopy Mission (XRISM) as well as the X-IFU spectrometer to be flown on Athena.
This work was supported by LLNL under Contract DE-AC52-07NA27344 and by NASA grants to LLNL and NASA/GSFC.