The X-IFU focal plane assembly development model: evaluation of the global magnetic shielding factor

This paper describes the evaluation of the global shielding factor of the Development Model (DM) of the X-ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) for the Athena X-ray observatory. We use a number of TES detectors spread over the south quadrant of the array as very sensitive magnetometers. We discuss the difficulties in performing a measurement like this where a Helmholtz coil outside the cryostat were used to apply a small magnetic field (< 200 µH) in order to avoid any permanent magnetization of the cryo mu metal (CMM) shield. Both AC and DC external magnetic fields have been applied at different orientation respect to the detector plate. Preliminary results set a lower limit in the evaluation of the global FPA shielding factor of ~ 10^5. Improvement in the measurement setup and in the analysis will be discussed and eventually applied to the following model of the FPA.