Revealing the Physics of the Hot and Energetic Universe via Single-Photon-Counting Advanced X-Ray Microcalorimeter Systems

Project Overview

Arrays of x-ray microcalorimeters using superconducting transition-edge sensors (TESs) offer the potential to provide high-resolution non-dispersive spectroscopy with exquisite energy resolution of about 2 eV from 0.1-20 keV. These attributes make the detectors especially well suited for x-ray astrophysics space missions and laboratory x-ray plasma diagnostics. A state-of-the-art microcalorimeter spectrometer under development by NASA and international partners will fly aboard the Athena x-ray observatory in the 2030s, a large (>$1 billion) satellite mission led by the European Space Agency. This instrument will enable observers to apply spectroscopic plasma diagnostics to study the physics of the hot and energetic universe, including investigations of black holes and the warped spacetime around them, clusters of galaxies, and the growth and evolution of galaxies. In addition, with some additional development, TES spectrometers can have a big impact on diagnostic capabilities for large fusion experiments such as ITER. However, count-rate limitations and the challenges in calibrating these TES microcalorimeter systems are increasingly recognized as limiting scientific potential. For example, there is no experimental verification that existing microcalorimeter designs can meet the Athena calibration requirements, in particular the required precision in absolute energy (wavelength) calibration needed for many of the primary science goals. For high-incident fluxes, the energy resolution degrades with existing pulse-processing techniques.

Our LDRD project aims to position LLNL to advance microcalorimeter instrument capabilities for both space and ground-based applications by addressing two areas of TES microcalorimeter system development and analysis: count-rate capability and calibration. Our work built upon our long-standing collaboration with NASA Goddard Space Flight Center while aiming to secure roles for LLNL in upcoming major x-ray astrophysics missions and to increase the scientific output of our existing microcalorimeter instruments used to study atomic physics to support LLNL core missions and astrophysics. To improve the count-rate capability of our microcalorimeter systems, we partnered with a research group at University of Wisconsin at Madison to develop processing code to apply advanced pulse-processing techniques to our laboratory spectrometers. We performed experiments to verify our approach to building a large-spot-size x-ray monochromator that can address challenges anticipated for Athena spectrometer calibration, and we worked on analysis to probe the details of TES microcalorimeter energy-gain scale with partners at GSFC. We also pursued an exciting opportunity to support a precursor to Athena that will launch a decade earlier: the Micro-X microcalorimeter sounding rocket, which launched in August 2022, providing an important technology demonstration and a novel x-ray spectroscopic observation of the Cassiopeia A supernova remnant.

Mission Impact

This work supports the science and technology capabilities and workforce that enable LLNL to deliver new national-security solutions and participate in collaborative, responsive efforts to emerging mission needs in space security and to support fusion experiments. Through this work, we met our exit-strategy milestone to secure a multiyear strategic partnership project on the NASA-funded Athena team, as well as roles within the Athena X-ray Integral Field Unit consortium for LLNL scientists. We successfully proposed to the DOE Office of Science Fusion Energy Sciences (FES) Measurement Innovation program to adapt microcalorimeter spectrometers for use on magnetic-fusion energy experiments; the three-year FES project leverages this LDRD work.

Publications, Presentations, and Patents

Witthoeft, M. C. et al. 2022. "Correcting Energy Estimation Errors Due to Finite Sampling of Transition-Edge Sensor Data." Journal of Low Temperature Physics 209, 1000-1007 (2022); doi:10.1007/s10909-022-02710-2.