Design of the charged particle diverter for the ATHENA mission

The large Halo orbit in L2 of the ATHENA mission will expose the spacecraft (SC) to a significant flux of charged particles which is expected to overlap with the energy range of the instruments. This is a source of measurement background that needs to be minimized as much as possible to achieve the strict requirements of the mission. The need to know and mitigate this type of background has been identified as critical, and has led to a number of technology development activities which are progressing in parallel to the Phase A activities. Particularly, this paper details the status of the on-going activities to develop a set of charged particle diverters whose goal is to reduce the background generated by soft-protons which are focused by the Silicon Pore Optics (SPO) mirror modules towards the instrument detectors. This paper explains the considerations leading to an accommodation of the charged particle diverters close to the instruments in the Science Instrument Module (SIM), and details the analytical approach followed to choose the mass-optimal location for the case of a uniform magnetic field Halbach design. The case of graded (non-uniform) magnetic fields is also explained in an effort to further decrease the mass. Preliminary magnetic field maps are presented as a proxy to compare the mass from different options. Finally, the first engineering models, manufacturing and test plans are presented which are the focus of a technology development activity aiming at the validation of the technologies involved up to TRL5.