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This document summarizes the work performed at the University of Kiel (\acs{CAU}) for the \acs{ATHENA} High Energy Particle Monitor (\acs{AHEPaM}) demonstration model (\acs{DM}) project. It provides the key properties of \acs{AHEPaM}, describes the design of \acs{AHEPaM}, compares its expected performance with the original measurement requirements, discusses possible future trade studies, and gives an assessment of the current Technology Readiness Level (\acs{TRL}) of \acs{AHEPaM}.
The proposed design of \acs{AHEPaM} combines different detection techniques to measure and identify electrons, protons, and alpha-particles (He nuclei) across the wide required energy range (0.05 -- 1 GeV for electrons and 0.1 -- 2 GeV for protons). The required time resolution, however, could not be met for all particle species within the allocated resources. Because very-high-energy ($>$ 50 MeV) electrons are so rare in the heliosphere, their measurement can not be performed within the statistical uncertainties and time resolution envisaged for \acs{AHEPaM}. This situation can be improved by simultaneously operating \acs{AHEPaM} in two measurement modes. In one mode \acs{AHEPaM} would be much better at resolving electrons from protons, but at less time resolution, in the other mode \acs{AHEPaM} would not separate them as well but would provide better counting statistics and thus time resolution. The proposed \acs{AHEPaM} would operate and provide data in both modes simultaneously. We have proposed to relax the measurement requirements on electrons. There are no processes in the heliosphere known to us that would modulate $>$ 50 MeV electrons at the time scales originally required. On the other hand, the proposed \acs{AHEPaM} satisfies the measurement requirements for protons and helium as well as the technical and engineering requirements. In addition, a slightly higher telemetry rate (a few kbps instead of 1 kbps) would provide scientifically interesting data to the heliophysics community.
%As discussed in the clarification meeting on April 4, 2022, we would appreciate an increase by a few kbps. The exact value needs to be determined and will be communicated to ESA. Then we will need to agree on what can be done.
