Ground calibration plan for the Athena/X-IFU microcalorimeter spectrometer

This paper describes the strategy and planned implementation of the ground calibration of the X-IFU microcalorimeter spectrometer on-board Athena, the X-ray observatory from ESA to be launched after the mid-2030s. X-IFU is the second generation of space microcalorimeter instrument, and its calibration strategy benefits from the experience acquired on the present Japanese-US built Resolve instrument on-board XRISM. This calibration plan takes into account the reformulation of the Athena mission and its instruments that took place in 2022-23. The X-IFU calibration strategy is presented along with the set of X-ray sources needed for the ground calibration and the the definition of the sequences for using them.