  The X-IFU (X-ray Integral Field Unit) onboard the large ESA mission Athena
(Advanced Telescope for High ENergy Astrophysics), planned to be launched in
the mid 2030s, will be a cryogenic X-ray imaging spectrometer operating at 55
mK. It will provide unprecedented spatially resolved high-resolution
spectroscopy (2.5 eV FWHM up to 7 keV) in the 0.2-12 keV energy range thanks to
its array of TES (Transition Edge Sensors) microcalorimeters of more than 2k
pixel. The detection chain of the instrument is developed by an international
collaboration: the detector array by NASA/GSFC, the cold electronics by NIST,
the cold amplifier by VTT, the WFEE (Warm Front-End Electronics) by APC, the
DRE (Digital Readout Electronics) by IRAP and a focal plane assembly by SRON.
To assess the operation of the complete readout chain of the X-IFU, a 50 mK
test bench based on a kilo-pixel array of microcalorimeters from NASA/GSFC has
been developed at IRAP in collaboration with CNES. Validation of the test bench
has been performed with an intermediate detection chain entirely from NIST and
Goddard. Next planned activities include the integration of DRE and WFEE
prototypes in order to perform an end-to-end demonstration of a complete X-IFU
detection chain.
