Characterization of a transition-edge sensor-based anti-coincidence detector for future large field-of-view X-ray calorimetry missions

Abstract

Microcalorimeter instruments aboard future X-ray observatories will require an anti-coincidence (anti-co) detector to veto charged particle events and reduce the non-X-ray background. We have developed a large-format, transition-edge sensor (TES)-based prototype anti-coincidence detector that is particularly suitable for use with spatially extended (~10 cm²) TES microcalorimeter arrays, as would be used for future large field-of-view X-ray missions. This prototype was developed in the context of the Line Emission Mapper (LEM) probe concept, which required a ~14 cm² anti-co detector with >95% live time and a low-energy threshold below 20 keV. Our anti-co design employs parallel networks of quasiparticle-trap-assisted electrothermal feedback TESs (QETs) to detect the athermal phonon signal produced in the detector substrate by incident charged particles. We developed multiple prototype anti-co designs featuring 12 channels and up to 6300 QETs. We focus on a design utilizing tungsten TESs and present characterization results. Broad energy range measurements have been performed (4.1 keV to 5.5 MeV). Based on noise and responsivity measurements, the implied low-energy threshold is 96% can be achieved up to 5.5 MeV for a LEM-like configuration. We also find evidence of millimeter-scale-or-better spatial resolution and discuss the potential utility of this for future missions. Finally, we discuss the early development of a solid-state physics model of the anti-co toward understanding phonon propagation and quasiparticle production in the detector.