Simulation of TES X-ray Microcalorimeters Designed for 14.4 keV Solar Axion Search

This study attempted to develop detection methods for solar axions using transition-edge-sensor (TES) microcalorimeters. Since the axion absorber comprised of iron-57 (⁵⁷Fe) is electroplated upon the membrane instead of directly onto the TES itself (with the absorber hence thermally connected to the TES via a gold thermal strap), some of the heat deposited into the absorber consequently escapes into the heat bath through the membrane before being detected by the TES. If the heat-loss depends upon the axion interaction position within the absorber, position dependence may degrade the energy resolution. Therefore, this study endeavored to evaluate the dependence of heat-loss and pulse shape on axion incident position with the COMSOL Multiphysics software package (using a finite element method). In addition, heat-loss and pulse shape were likewise evaluated when the energy was deposited directly within the gold thermal strap.