Laboratory Astrophysics Studies of X-ray Spectral Signatures of High-Temperature, High-Density Plasmas

With the recent launch of the microcalorimeter Resolve, onboard the Xray Imaging and Spectroscopy Mission (XRISM), X-ray astrophysics is entering a new era of space-based, high-resolution X-ray spectroscopy. Traditionally, most astrophysical models have neglected high-density effects, such as Stark broadening, ionization potential depression, density-dependent line shifts, and suppression of dielectronic recombination because many astrophysical sources are relatively low density. However, significant progress over the past decade has been made to incorporate these effects into astrophysical models to, for example, understand better the physics of accretion disks surrounding black holes. In fact, in the case of black hole accretion disks, including high-density effects has brought the iron abundance inferred from the measured spectrum from highly over-abundant to closer to the expected Solar abundance. Despite these advances, experimental benchmarks in this density regime remain scarce. To address this gap, we are developing an experimental platform using Lawrence Livermore National Laboratory’s frequency doubled, shortpulse Titan laser coupled with high-resolution, time-integrated crystal spectrometers to create and measure X-ray emission from highly charged ions in the high density (> 10²³ cm⁻³), high-temperature regime (∼ 1 keV). This platform will improve our understanding of high electron density effects on atomic structure and provide X-ray benchmarks for spectral modeling packages used by the high energy density and high energy astrophysics communities.

This work was supported by the U.S. DOE Office of Science, Fusion Energy Sciences under Field Work Proposal No. SCW1836-1: LaserNetUS: Discovery Science and Inertial Fusion Energy research at the Jupiter Laser Facility, and Lawrence Livermore National Laboratory, under Contract No. DE-AC52-07NA27344.