  The last generation of X-ray focusing telescopes operating outside the
Earth's radiation belt discovered that optics were able to focus not only
astrophysical X-ray photons, but also low-energy heliophysical protons entering
the Field of View (FOV). This "soft proton" contamination affects around 40\%
of the observation time of XMM-Newton. The ATHENA Charged Particle Diverter
(CPD) was designed to use magnetic fields to move these soft protons away from
the FOV of the detectors, separating the background-contributing ions in the
focused beam from the photons of interest. These magnetically deflected protons
can hit other parts of the payload and scatter back to the focal plane
instruments. Evaluating the impact of this secondary scattering with accurate
simulations is essential for the CPD scientific assessment. However, while
Geant4 simulations of grazing soft proton scattering on X-ray mirrors have been
recently validated, the scattering on the unpolished surfaces of the payload
(e.g. the baffle or the diverter itself) is still to be verified with
experimental results. Moreover, the roughness structure can affect the energy
and angle of the scattered protons, with a scattering efficiency depending on
the specific target volume. Using Atomic Force Microscopy to take
nanometer-scale surface roughness measurements from different materials and
coating samples, we use Geant4 together with the CADMesh library to shoot
protons at these very detailed surface roughness models to understand the
effects of different material surface roughnesses, coatings, and compositions
on proton energy deposition and scattering angles. We compare and validate the
simulation results with laboratory experiments, and propose a framework for
future proton scattering experiments.
