Modeling the effects of position dependence in large-absorber x-ray TES microcalorimeters

Abstract

We present finite element simulations of the transition-edge sensor (TES) microcalorimeter behavior using COMSOL Multiphysics. The simulated detector has a large absorber with a size of 990×990μm2. The simulation calculates the TES response after x-ray impact for a single pixel with a known, realistic, current-dependent resistive transition R(T,I). The simulation includes the full electrothermal feedback effects and heat conduction through the multiple contact points of the absorber to the TES thermometer and supporting membrane. The presented model, especially the 2D model, has been optimized for high accuracy, making it suitable for simulating the detector response when incident photons hit different positions on the absorber. We study the effects of position dependence using Principal Component Analysis with the aim of extracting correct photon energies from the pulses. The simulations show that the degradation, i.e., the FWHM broadening, due to the pulse variations will be less than 0.7 eV at below 2 keV, while it can be significant (>1 eV) at a higher energy band. The simulation result for position dependence can guide the design of large-absorber detectors for future x-ray missions, such as the Hot Universe Baryon Surveyor.