\section{Summary}
\label{sec:summary}
The \ac{AHEPaM} is proposed to serve as a particle instrument on \ac{ATHENA}, monitoring precisely the high-energy particle fluxes of electrons, protons and helium particles which dominate the background signal of x-ray telescopes. The instrument is designed as a stack of \acp{SSD} which allow for the measurement of differential energy-losses of traversing particles as well as defining the view-cone of the instrument. These detectors are complemented by two \ac{BGO} scintillators in-between the \acp{SSD} which provide sufficient stopping power for lower energetic particles and improve electron-proton separation due to electro-magnetic shower caused by electrons in the heavy \ac{BGO}. Furthermore, a trade-off analysis for adding two Cherenkov-detectors to the \ac{SSD} stack has been performed. The Cherenkov-detectors would improve particle separation (especially electron vs. proton identification) while introducing further technical complexity to the instrument due to the necessarity of \acp{PMT} and their high-voltage. The measurement uncertainties (both statistic and systematic) that are to be expected from the proposed instrument in the \ac{GCR} radiation field have been calculated and are presented for different temporal resolutions and measurement modes. For instance, \ac{AHEPaM} can achieve flux uncertainties down to 1.2\%  for five protons channels based on a 10ks time resolution and to 2.5\% for two electron channels based on a 100ks time resolution. \newline
Structural and thermal modelling has also shown that while being challenging, the engineering requirements can definitively be met by the proposed instrument.


