Effect of Space Radiation on Transition-Edge Sensor Detectors Performance

The Athena mission and its X-ray Integral Field Unit (X-IFU) instrument will be positioned at the Sun-Earth Lagrange point L1, where it will be subject to particles from the solar wind with energy below 0.1 MeV, and from galactic cosmic rays and solar flares with energies up to hundreds of MeV for protons and GeVs for heavier ions. Some of these particles will go through the satellite and hit the focal plane assembly and hence the detectors. These detectors will be TES (Transition-edge sensor) microcalorimeters, flown for the first time in such an environment. In order to ensure the performance of this type of detector throughout the duration of such a mission, it is critical to study the impact of the radiation on their behavior. Indeed, although a lot of reference material exist for semiconductor-based photodetectors such as CCDs and CISs, little is currently known about the impact of radiation on TES detectors. These energetic events could cause local heating or damage to the detectors and affect their performance. In this work, we describe how we designed a test campaign to assess the impact of L1 radiation on TES detectors for Athena/X-IFU-like missions and present the results of the tests, for a maximum dose of 4.3 krad(Si)). Analysis includes assessing changes in the pulse shapes and energy resolution of the detectors measured at 55 mK after several radiation dose steps performed at 4 K.