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Updates on simulating non-equilibrium ionization plasmas with the LLNL EBIT-I electron beam ion trap

Presentation #103.69 in the session Missions and Instruments.

Published onJul 01, 2023
Updates on simulating non-equilibrium ionization plasmas with the LLNL EBIT-I electron beam ion trap

In transient X-ray sources, such as supernova remnants (SNR), solar flares, and cluster shocks, prevalent heating or cooling mechanisms lead to the presence of plasmas in non-equilibrium ionization (NEI) conditions. These plasmas present as recombining plasmas (overionized, dominated by radiative recombination), ionizing plasmas (underionized, dominated by collisional ionization), or with an electron energy distribution with a high-energy tail deviating from a pure Maxwellian (kappa distribution). In many sources, the details of the mechanism leading to an NEI plasma are not yet well understood. While the spectra of current NEI models largely agree with each other, in observations of the brightest recombining SNR, they 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. As direct, high-resolution comparisons between different NEI models show larger deviations between models than is the case for different collisional ionization equilibrium (CIE) models, benchmarking NEI models is particularly important for interpretation of upcoming 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. Employing the Lawrence Livermore National Laboratory's EBIT-I electron beam ion trap and the NASA/GSFC ECS high-resolution calorimeter spectrometer, we measure X-ray line emission from highly charged ions of astrophysically relevant elements in NEI conditions. These NEI conditions are created by operating the EBIT Maxwellian simulator - programmed with either a standard Maxwellian or a kappa distribution — on trapped ions whose charge balance is over- or underionized compared to that of a corresponding CIE measurement. By benchmarking available NEI measurements with these data, our results will help to interpret existing and future observations of a variety of transient sources. Here we report an update on the progress of this work. This work was supported by LLNL under DOE Contract DE-AC52-07NA27344 and by NASA grants to LLNL and NASA/GSFC.

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