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cau-ath-fr_i1-0/cau-ath-fr.tex
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@ -138,6 +138,8 @@ The scope of this document is to provide a complete description of all the work
%\input{scope} # i have decided that this can go into the abstract, paddy, 30.05.23
\input{performance_analysis}
\input{thermal-analysis}
\input{structural-analysis}
\input{report}

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cau-ath-fr_i1-0/media/figs_sim/AHEPaM-documents.zip
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cau-ath-fr_i1-0/performance_analysis.tex
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\section{Performance analysis}
\label{sec:performance-analysis}
\graphicspath {{media/figs_sim}}
\graphicspath {{../cau-ath-djf-0007_i1-0/media/figs_sim}}
The performance of AHEPaM is analysed using a GEANT4 simulation. Section \ref{sec:sim_setup} introduces the simulation setup while sections \ref{sec:sim_stop} and \ref{sec:sim_pene} evaluate the performance for particles that stop in the instruments or penetrate it. Section \ref{sec:sim_verdict} summarizes the results. The formula used for the uncertainty estimation that takes into account contamination of different particle types is derivated in section \ref{sec:sim_error}.

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\section{Structural Analysis}
\label{sec:structural-analysis}
The inital \acl{SMM} \cite{smm} has been set up and analyzed at \acf{IDR} at \acf{UPM}. All figures presented in this chapter are taken from that report.\newline
The main purpose of the structural design is to provide the baseline for dimensioning every hardware component of \acs{AHEPaM} in a way, that it can withstand all mechanical loads induced during the whole mission. The most demanding missions phases are the verification and test phase, and the final launch phase. The main design concept is driven by a couple of factors:
\begin{itemize}
\item The telescope, including all particle detectors need to be arranged in a stacked arrangement which maintains the relative position of the elements at all times.
\item The particle detector carriers are potentially made of ceramic material (AlN or $Al_{2}O_{3}$) which can not tolerate large deformations of their bearing seat.
\item The \acs{BGO} crystals have a large mass of 1 kg per each and are located in the center of the telescope.
\item The analog electronics signal pathways needs to be minimized
\item Analog and digital signal side need to be separated and the analog side thoroughly shielded against external noise.
\end{itemize}
From the above list the main objectives of the structural design and thus the focus of the structural analysis has been derived such as:
\begin{enumerate}
\item The BGO-bracket needs to support the structural loads induced by the \acs{BGO}s.
\item Since the masses of the \acs{BGO} and the cherenkov sub assembly vary by two orders of magnitude, they will be excited at fundamentally different resonance frequencies. Thus the mechanical elements of the telescope need to be structurally coupled in order to avoid damage of the large SDB..SDD detectors.
\item The base-frame need to a) support the mechanical loads induced by the \acs{BGO}s and b) distribute them to the sides of the chassis sides.
\item The flow of forces shall be along the ebox chassis' outer walls towards the interface feet.
\end{enumerate}
By the time the initial modeling process started, the detailed design of the instrument's cover was not in a representative state. Thus it has been excluded from the presented SMM. It will be included in a future revision.\\
However the overall estimated mass of 350g is low compared to the instrument mass. Additionally a design has been chosen as presented in \cite{ahepam-ddf} that will have a high stiffness. It is therefore expected that a) the instrument cover will have a minor effect on the overall structure and b) that its dynamic behaviour will not be able to excite global modes.\newline Its influence on local modes of the assembly, especially regarding the particle detectors will be part of the above mentioned revision, as their geometric character (large sheet like elements) is similar.
\newpage
\subsection{Model Setup}
\label{sec:smm-detup}
The SMM has been set up using shell elements and has been analyzed using the \textit{NASTRAN} solver. In this initial design state it uses a relatively coarse mesh density focusing on quick iteration cycles rather than high accuracy.\\
The model has been set up following the instrument's FM-status design. That means the following results assume a full arrangement of electronics boards and FM-scale detectors. A tailored DM-status model has not been analyzed.\\
As defined in \cite{ahepam-req} the analyzis applied a static load of 30G \textit{R-AHEPaM-120} and the mission specific random vibration spectrum \textit{R-AHEPaM-160}.
\begin{figure}[h!]
\begin{subfigure}{0.5\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_chassis.png}
\caption[]{Structural model of \acs{AHEPaM}'s chassis.}
\label{fig:smm_chassis-mesh}
\end{subfigure}
% \hfill
\begin{subfigure}{0.5\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_ebox.png}
\caption[]{Structural model of \acs{AHEPaM}'s ebox.}
\label{fig:smm_ebox-mesh}
\end{subfigure}
\caption{Shell element meshes of \acs{AHEPaM}'s SMM element.}
\label{fig:smm_meshes}
\end{figure}
\subsection{Results}
\label{sec:smm-results}
\begin{itemize}
\item {Complying with \textit{R-AHEPaM-110}, the first global resonance over the whole frequency range up to 2000Hz is $\geq$140 Hz.}
\item The static load test showed positive margins of safety against yield \textit{MoSy} and ultimate stress \textit{MoSu} for all parts of the instrument. (\textit{R-AHEPaM-120})
\end{itemize}
\subsubsection{Effective Modal Mass}
\label{sec:smm-emm}
An important method of judging the behaviour of a structure is to determine the mass which is excited at a certain frequency, namely the \textit{Effective Modal Mass} (EMM) shown in tables \ref{tab:smm-emm1} to \ref{tab:smm-emm3}. In general low values can be considered as local modes, since they are locally occuring excitation of mostly single parts of the assembly. High values can be considered global modes, since the effect a larger number of parts and thus mass. In the scope of this report a mode is considered 'global' if it shows an EMM$>25\%$. Figures \ref{fig:smm-modes5-12} to \ref{fig:smm-modes68-109} show the dedicated mode shapes. \newline
\newpage
\begin{table}[h!]
\caption[Effective model masses list.]{Significant effective modal masses up to approx. 260 Hz.}
\centering
\includegraphics[width=.85\linewidth]{cau-ath-djf-0007_i1-0/media/smm2_emm1.png}
\label{tab:smm-emm1}
\end{table}
\begin{table}[h!]
\caption[Effective model masses list.]{Significant effective modal masses up to approx. 593 Hz.}
\centering
\includegraphics[width=.85\linewidth]{cau-ath-djf-0007_i1-0/media/smm2_emm2.png}
\label{tab:smm-emm2}
\end{table}
\begin{table}[h!]
\caption[Effective model masses list.]{Significant effective modal masses up to approx. 1100 Hz.}
\centering
\includegraphics[width=.85\linewidth]{cau-ath-djf-0007_i1-0/media/smm2_emm3.png}
\label{tab:smm-emm3}
\end{table}
\begin{figure}[h!]
\begin{subfigure}{0.425\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mode5.png}
\caption[]{Mode shape 5.}
\label{fig:smm-mode5}
\end{subfigure}
\hfill
\begin{subfigure}{0.425\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mode12.png}
\caption[]{Mode shape 12.}
\label{fig:smm-mode12}
\end{subfigure}
\caption{Global Modes 5 and 12.}
\label{fig:smm-modes5-12}
\end{figure}
\begin{figure}[h!]
\begin{subfigure}{0.425\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mode22.png}
\caption[]{Mode shape 22.}
\label{fig:smm-modes22}
\end{subfigure}
\hfill
\begin{subfigure}{0.425\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mode54.png}
\caption[]{Mode shape 54.}
\label{fig:smm-modes54}
\end{subfigure}
\caption{Global Modes 22 and 54.}
\label{fig:smm-modes22-54}
\end{figure}
\begin{figure}[h!]
\begin{subfigure}{0.445\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mode68.png}
\caption[]{Mode shape 68.}
\label{fig:smm-modes68}
\end{subfigure}
\hfill
\begin{subfigure}{0.405\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mode109.png}
\caption[]{Mode shape 109.}
\label{fig:smm-modes109}
\end{subfigure}
\caption{Global Modes 68 and 109.}
\label{fig:smm-modes68-109}
\end{figure}
\newpage
After the modal, the random vibration analysis has been performed by applying the dedicated input spectrum to the model's interface, the feet.\newline
The objective is to find locations throughout the structure which exceed their allowed materials' strength, most prominent the material's yield strength. Table \ref{tab:smm-mos} shows the parts' materials together with the stress, the part has encountered during the analysis. The SMM-report \cite{smm} shows fringe plots for all parts that exceeded their material's threshold. In the scope of this report just an exemplary plot (figure \ref{fig:smm-bgo-fringe}) is shown.
\begin{figure}[h!]
\begin{subfigure}{0.65\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_mos.png}
\caption[]{Negatvie MoS indicate too high mechanical stresses.}
\label{tab:smm-mos}
\end{subfigure}
%\hfill
\begin{subfigure}{0.35\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-djf-0007_i1-0/media/smm2_fringe-plot-1.png}
\caption[]{Exemplary fringe plot of BGO-bracket.}
\label{fig:smm-bgo-fringe}
\end{subfigure}
\caption{Margins of safety derived from random vibration analysis.}
\label{fig:smm-random}
\end{figure}
\subsection{Discussion}
\label{sec:smm-discussion}
At low frequencies, the global modes occur at the telescope and the bottom plate. They are isolated translational modes, which oscillate along the instruments Y-axis. That is not surprising, since that's the long axis of the instrument chassis' extension and can be considered as the 'soft' axis.\newline
It's important to mention that the presented initial model has been set up with reduced detail level of the included mechanical features. The sheet thickness of the base frame (the interface of the telescope) for example has been implemented with a homogeneous thickness of 4mm, while the underlying CAD-model has been modeled using a sheet thickness of 3mm and stiffening ribs (connecting all boreholes) of 7.5mm. It is assumed that the dynamic behaviour of these features will significantly influence the behaviour and might improve the current results.\newline
More interesting are the higher frequency global modes, because here the boards and the telescope resonate at similar frequencies. In upcoming iterations, with a higher level of detail, it has to be thoroughly investigated if a cross talk is taking place at these elements. If it turns out to be the case, the design will be adapted in order to better separate these modes.\newline
From this first run it can be positively concluded that the chosen coupling of the telescope elements blocks out relative movement in the given frequency range.\newline The analysis also shows negative margins of safety at several parts along the load path of the instrument. While this needs undoubtedly to be improved, it has to be kept in mind that these are findings of the initial preliminary model run. The presented MoS-exceedances can without exceptions be summarized under the premise, that for the given mass of the BGOs a too low plate thickness at the interfaces has been chosen.\newline By increasing the sheets' material thicknesses and/ or increasing the bolt sizes it is expected to bring the current negative values into the necessary positive regime.\\
Although negative aspects have been found by the presented structural analysis it is concluded that the outcome is very positive, since it provides an initial inside view into the structural behaviour of the presented instrument design and significantly helped in locating momentary weak spots which can now be improved. Additionally these spots can relatively easy be modified from an instrument design perspective.\\
\subsection{Next Steps}
\label{sec:smm-next steps}
During the project's next phase, the following steps shall be included in a revised CAD model and the subsequent \acs{SMM}.
\begin{itemize}
\item Include relevant cad-modeled structural shape (stiffening ribs) of all parts included in the load path in the \acs{FEA} mesh.
\item Review CAD model towards findings of SMM and adapt where necessary.
\item Include missing instrument cover in the SMM.
\item Review potential cross talk between telescope and PCBs at higher modes ($~>400$Hz).
\end{itemize}

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\section{Thermal Analysis}
\label{sec:thermal-analysis}
The inital \acl{TMM} \cite{tmm} has been set up and analyzed at \acf{IDR} at \acf{UPM}. All figures presented in this chapter are taken from that report.\newline
\textit{ESATAN} has been used to perform the analysis. The current model is a low resolution nodal network with one node representing every main mechanical component with manually calculated thermal masses and conductances applied to it. For the moment just steady state cases have been studied, which end up in a thermal equilibrium of the structure depending on the chosen inputs. Figure \ref{fig:tmm-nodal-network} shows the details of it.
\begin{figure}[h!]
\centering
\includegraphics[width=1\linewidth]{cau-ath-djf-0007_i1-0/media/tmm_node-network.jpg}
\caption[The schematic of the baselined node-network]{Schematic of the TMM as a nodal network.}
\label{fig:tmm-nodal-network}
\end{figure}
\subsection{Design Drivers}
\label{sec:tmm-design-drivers}
The main thermal design drivers of \acs{AHEPaM} are the temperatures of the a) particle detectors and b) the \acf{PMT}. The electronics noise the silicon of the detectors produces is correlated to its temperature, with lower temperature producing less noise. Heritage shows that 0$^{\circ}$C is the ideal temperature for \acs{AHEPaM}'s detectors. That's even more true if little energies need to be detected.\newline
The second design driver is -30$^{\circ}$C for the \acs{PMT} in both the cold op- and non-op case. This is a value defined by the manufacturer, provided in the element's datasheet.\newline
Since this sets a limiting threshold at a comparatively high temperature, the instrument team is currently investigating the justification behind this value and if it can be relaxed towards colder values.\newline
Nevertheless, since at the time of writing mitigation is still under investigation, this value is part of the \acs{TMM}.
\subsection{Design Elements}
\label{sec:tmm-design-elements}
The different main design elements are described in \cite{ahepam-ddf} and are not repeated here.
\subsection{Boundary Conditions}
\label{sec:tmm-boundary-conditions}
As outlined in \cite{ahepam-ddf} key thermal design parameters which are not yet available have been chosen in order to conduct the simulation. More specific, a value for solar heating due to the sun's illumination has been applied. This limits the applicability of the results to a specific scenario, described in the following chapters. The benefit is that this approach provides information to put the units behaviour into perspective and allows to extrapolate from it.\\
The following general boundary conditions have been applied:
\begin{itemize}
\item The unit is fully insulated, except for:
\begin{itemize}
\item its conductive interfaces.
\item its radiative interfaces.
\end{itemize}
\item There are two external heat sources:
\begin{itemize}
\item the sun at 1 AU.
\item the conductive interface with the \acs{S/C}.
\end{itemize}
\item There are three potential heat sinks, depending on the scenario
\begin{itemize}
\item radiative coupling with space through the instruments surface.
\item radiative coupling with space through external radiator 'applied' to the ebox' chassis frames.
\item the S/C interface with an assumed $\infty$ thermal capacity.
\end{itemize}
\end{itemize}
Consequently there is \textit{no} heat exchange with the surface of the \acs{S/C} or other (unknown) appendages, e.g. other payload.
\subsection{Studied Cases}
\label{sec:tmm-cases}
The following scenarios have been studied
\begin{itemize}
\item[] A.1) Hot-operational.
\begin{itemize}
\item[] {The sun at a distance at 1 \acs{AU} illuminates 1 face of the pyramid-shaped instrument cover. The cover has the optical properties of \acs{OSR}s, means a high IR emissivity and a low solar absorption. The opposite side of the instrument cover is used as a radiator.\newline \newline
Heat sources: I/F at +40$^{\circ}$C, instrument dissipates 8.86W in total, sun at 1 AU through instrument cover.\newline
Heat sinks: Instrument cover.}
\end{itemize}
\item[] A.2) Hot-operational with additional external Radiator.
\begin{itemize}
\item[] {Same as before, just with an external radiator of approx. 10cm x 10cm applied to each of the three ebox chassis frames.\newline \newline
Heat sources: I/F at +40$^{\circ}$C, instrument dissipates 8.86W in total, sun at 1 AU through instrument cover.\newline
Heat sinks: Instrument cover, external radiator with a total area of rounded 0.03m$^2$.}
\end{itemize}
\item[] B.1) Cold Operational.
\begin{itemize}
\item[] {Now, as the other extreme, the I/F temperature is changed to -40$^{\circ}C$ and the additional heat intake from the sun is switched off.\newline \newline
Heat sources: Instrument dissipates 8.86W in total.\newline
Heat sinks: I/F at -40$^{\circ}$C, 1 side of the instrument cover.}
\end{itemize}
\item[] {B.2) Side case: Spot heating at the cherenkov frames in order to lift the \acs{PMT} temperature.}
\begin{itemize}
\item[] {Here, with the same interface setting as B.1 before, spot heating of 0.328W per cherenkov chassis has been applied. The goal is to see the effect on the PMT, since it has a cold temperature threshold of -30$^{\circ}$C.\newline \newline
Heat sources: Instrument dissipates 8.86W in total, 2x 0.328W spot heating.\newline
Heat sinks: I/F at -40$^{\circ}$C, instrument cover.}
\end{itemize}
\item[] C.1) Cold Non-operational.
\begin{itemize}
\item[] {In the non-op case no power is applied or dissipated by the unit.\newline \newline
Heat sources: None.\newline
Heat sinks: I/F at -40$^{\circ}$C, instrument cover.}
\end{itemize}
\item[] C.2) Cold Non-operational with survival heating power.
\begin{itemize}
\item[] {In order to prevent the minimum threshold of -30$^{\circ}$C at the \acs{PMT}s 5.265W is applied at the base frame. A safety margin of 5$^{\circ}$C for the \acs{PMT} is included.\newline \newline
Heat sources: 5.265W of survival heating power at the base-frame.\newline
Heat sinks: I/F at -40$^{\circ}$C, instrument cover.}
\end{itemize}
\end{itemize}
\newpage
\subsection{Results}
\label{sec:tmm-results}
The results are verified against the design temperature of the particle detectors A to E (\textit{SDA .. SDE} and the \acl{PMT} of the cherenkov detectors. Their specific temperature are listed at the right in table \ref{tab:tmm-results}.
\begin{table}[h!]
\caption[Results List.]{TMM Results}
\centering
\includegraphics[width=1\linewidth]{cau-ath-djf-0007_i1-0/media/tmm_2nd_results-table.pdf}
\label{tab:tmm-results}
\end{table}
\subsection{Discussion and Next Steps}
\label{sec:tmm-next-steps}
The results clearly indicate that in case the instrument receives external heat for such a long time, that it reaches its equilibrium temperature, it is going to need a radiator. Looking at the effect of the analyzed radiator area and taking the shape of the instrument into account, the surface of the instrument cover could calculatively be sufficient to lower the temperature to the design temperature.\newline However depending on the location on the S/C the accommodation of \acs{AHEPaM} might become very complex, since the instruments performance would probably be strongly depending on external illumination, e.g. light reflections of payload or S/C appendages.\newline An external radiator might be beneficial, because (given appropriate thermal straps or conductive connection in general) such an element could be accommodated in permanent shadow and thus would, together with \acs{MLI}, that could be used in that scenario, lead to a significantly more robust instrument design.\\
Additionally the results show, that if a radiator is required and it can (at the first assumption) not be switched on or off, it would reduce the instrument temperature well below the cold threshold of the PMT. Case B.1 gives a hint on what might happen. Unfortunately B.1 is overly optimistic, since it does not include the cooling effect of the external radiator, analyzed in A.2. Consequently it can be assumed, that, in case of a radiator, OP-heating in the range of 5W would be required.\\
Finally the need for survival heating power is obvious, see C.2, if the minimum threshold of -30$^{\circ}$C can not be mitigated, means shifted towards colder temperatures.\\
So it can be concluded, that the accommodation of \acs{AHEPaM} on the \acs{ATHENA} \acs{S/C} has a driving influence on adapting the thermal design and the need of heating power. Furthermore it should be thoroughly investigated, if the \acs{PMT} can be operated and stored in colder conditions.
% \begin{table}[h!]
% \centering
% \caption{Telescope FM/ DM design differences.}
% \label{tab:telescope-diffs}
% \begin{tabular}{lll}
% \hline
% & \multicolumn{1}{c}{\textit{\textbf{FM}}} & \multicolumn{1}{c}{\textit{\textbf{DM}}} \\
% \hline
% \textit{Positioning} & $\vert50\vert30\vert30\vert50\vert$ & \begin{tabular}[c]{@{}l@{}}$\vert51.4\vert27.3\vert30\vert51.4\vert$ \end{tabular} \\
% \hline
% \end{tabular}
% \end{table}

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cau-ath-sr_i1-0/cau-ath-sr.tex
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@ -137,6 +137,9 @@ The scope of this document is to provide a summary of all the findings of the \a
%\input{scope} # i have decided that this can go into the abstract, paddy, 30.05.23
\input{design-description}
\input{specifications}
\input{performance_results}
\input{report}

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\section{Scope}
\label{sec:scope}
The scope of this document is to describe the design details of the \acs{AHEPaM} instrument. The model philosophy of the underlying contract is to physically built a \acl{DM} and to implement as many design details of a \acl{FM} as feasible. The \acs{DM} shall show feasibility of the measuring concept and to key mission requirements and shall allow to approximate the functionality of a later \acs{FM}. The overall instrument design is thus derived from a \acs{FM} instrument design. That means all technical aspects such as detector and derived channel count and consequently required \acs{PCB} space, power and size requirements are designed to comply with the proposed FM requirements.\\
In order to keep building cost low, the \acs{DM} will be built using stock parts from previous space missions or \acs{OTS} components (e.g. detectors) where possible. In case no residual parts are available, footprint and shape of new components will be chosen to provide compatibility with the later FM design. Following this approach the \acs{DM} performance will be tailored to show proof-of-concept capabilities, but will not provide the full range of capabilities as a later \acs{FM}.\\
Verification by test will focus on those aspects which are either new processes, which have been introduced especially for AHEPaM and for which, on principle, the instrument team cannot provide heritage for, which are considered critical for the instrument's basic functioning or if the suitability can't be sufficiently satisfied by analysis.\\
To combine both aspects, following FM design requirements on one hand and use residual parts on the other hand, the final \acs{DM} design will be adapted on certain locations by suitable means in order to accommodate the above mentioned different form factors or shapes and will thus deviate from the final FM design.\\
Since the instrument development is ongoing, some aspects like the Cherenkov-detector design together with \acs{PMT} coupling and reading are not yet finalized. Consequently the way the DM is built is a best-effort approach to approximate the final FM. Findings from the \acs{DM} verification campaign and/ or assembly process will be thoroughly reviewed and will find their way into a final \acs{FM}.\\
Chapter \ref{sec:differences} lists the differences between DM and FM.
\newpage
\section{Basic Instrument Design of FM/ AHEPaM}
\label{sec:basic-design}
Since the \acs{DM} is derived from a flight model instrument design it is valuable to understand the underlying design ideas. The following chapter describes the design aspects of \acs{AHEPaM} baselining the FM configuration as a reference.\\
Chapter \ref{sec:differences} will afterwards list the differences between the two statuses and will discuss the trade-offs that have been made.
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam_with-cover.png}
\caption{\centering{AHEPaM with its instrument cover (purple) on top of the \acs{EBox} (green).}}
\label{fig:ahepam-with-cover}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam_without-cover.png}
\caption{\centering{The instrument cover (not visible) shields the telescope (blue) against light and electronics noise.}}
\label{fig:ahepam-wo-cover}
\end{subfigure}
\caption[Two pictures showing AHEPaM's telescope on top of the ebox. With and without instrument cover.]{CAD-views of AHEPaM's principle arrangement.}
\label{fig:basic-arrangement}
\end{figure}
\subsection{Arrangement}
\label{sec:arrangement}
\acs{AHEPaM} uses a stacked configuration of its functional components: The telescope, including all detectors is mounted on the \acs{EBox} (figures \ref{fig:ahepam-wo-cover}, \ref{fig:ebox-board-stack}), which itself consists of three chassis frames that accommodate the electronics infrastructure: (figure \ref{fig:ebox-board-stack}) analog, digital, \acs{LVPS} and \acs{HVPS} board. This arrangement keeps analog signal lines short and provides good accessibility for mounting and potential rework. Additionally the analog signal side can be shielded effectively against electronics noise by generating a de facto faraday cage between the el. conductive instrument cover and the \acs{EBox} chassis.
\begin{figure}[h!]
\centering
\includegraphics[width=0.75\linewidth]{cau-ath-ddc-0006_i1-0/media/athena_stacked-boards.png}
\caption[CAD-View showing AHEPaMs ebox' board arrangement.]{FM-\acs{AHEPaM}'s electronics boards' arrangement: Preamp-\acs{PCB}s (red) on top, followed by filter/ shaper-PCBs (green). The backend-PCBs are located at the bottom.(blue)}
\label{fig:ebox-board-stack}
\end{figure}
\subsection{Telescope}
\label{sec:telescope}
The sub assembly which defines \acs{AHEPaM}'s outer shape and subsequent arrangement is the telescope consisting of the central BGO-sub-assembly, which is a stacked arrangement of two hexagonal \acs{BGO} and three silicon twin detectors (figure \ref{fig:fm-telescope-if-details}). This group is surrounded on two face sides by the \acl{CHKV} sub-assemblies which consist of the aerogel based Cherenkov detector and its accompanying readout \acs{PMT}, together with the \acs{PMT}'s HV-electronics. An additional twin detector is located on every \acs{CHKV} chassis. This setup results in a five twin \acs{PIPS}-detectors telescope, which allows \acs{AHEPaM} to measure particles coming from two opposing viewing directions.\\
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-fm_top_telescope-wo-dets.png}
\caption{\centering{FM-telescope only showing the particle detectors. (BGO in transparent purple, Cherenkov in transparent yellow)}}
\label{fig:fm-telescope-wo-readout}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-fm_top_telescope.png}
\caption{\centering{FM-telescope showing the particle and the readout detectors. (grey for the BGO, green (the PMTs) for the Cherenkov) }}
\label{fig:fm-telescope-w-readout}
\end{subfigure}
\caption{AHEPaM's FM telescope arrangement.}
\label{fig:fm-telescope-if-details}
\end{figure}
\subsection{Detector design}
\label{sec:detector-design}
AHEPaM utilizes different detector types in its telescope.
\begin{itemize}
\item SSD\\
\acl{SSD} are standard detectors in particle physics, providing an electrical charge signal proportional to the energy deposited in its volume by a charged particle. Every \acs{SSD} is comprised of at least 4 segments. An inner one, surrounded by three identical sized channels in a 120 degree pattern, where the three allow for a certain angular resolution of the detector. The \acs{SSD} of the BGO-sub-assembly have another large outer segment utilized as anti-coincidence. For the \acs{DM} we will re-use a proven design from the \acl{HET} instrument on \acl{SO}, which are single-pixel detectors. Although this is a detector design from a previous instrument, the instrument team wants to test details of \acs{AHEPaM}s flight detector design. Therefore new detectors, based on the described layout are being manufactured an are assembled on special carriers, which resemble the intended FM carrier design, but allow the mounting of the given detector shape.
\item BGO\\ Materials that are emitting light after energy deposition by an energetic particle are called scintillators. Since this light output is proportional to the deposited energy, the read-out signal of i.e. an photodiode attached to the scintillator can be used to measure the energy loss of particles. Based on experiences with \ac{RAD} \cite{hassler-etal-2012} and Solar Orbiters \ac{HET} \cite{Pacheco-etal-2020}, we opted for a \ac{BGO} scintillator and a photodiode read-out. The \ac{BGO} has a high mean atomic number as well as a high density which results in a high stopping power which is beneficial for fullfilling measurement requirements. The disadvantages of a \ac{BGO} scintillator, temperature dependency \cite{elftmann-etal-2019} and non-linearities for heavy particles \cite{birks-1951,tammen-etal-2015}, are well understood previous missions have shown that we can be correct these effects.\\
Both \acp{BGO} share the same dimensions of 20mm thickness and a wrench size of 90mm resulting in a mass of m=1000g per unit due to the high materials' density. This makes them the most heavy components of the telescope and by that drive some of the structural parameters of AHEPaM's design.
\item Cherenkov-Detectors\\
Two 62mm x 62mm x 40mm aerogel cubes built the Cherenkov detectors which are located at the two sides of the main telescope axis (figure \ref{fig:dm-telescope-w-readout}). In contrast to the \acp{BGO} these parts just weigh a few grams, so mechanical structural support is a minor issue here. A significat design aspect arises from the fact that aerogel is very brittle at the edges and comes, as a manufacturing characteristic, with large geometric shape tolerances, which need to be adressed and dealt with by the part's support structure.\\
The Cherekov detectors are being read-out by \acp{PMT}. Since these elements count single photons external straylight needs to be omitted at all circumstances. Hence the \acs{CHKV} housing acts as a light box which needs to be fully light tight.\\
The detailed mechanical support design is ongoing and is part of the mechanical verification activities of the \acs{DM}.
\end{itemize}
It is currently under investigation if the Cherenkov-detector needs to be protected against moisture to maintain it's optical specifications. Thus it is foreseen to provide purging provisions in the chassis in case GN2-purge becomes necessary.
\subsection{Detector Carriers}
\label{sec:det-carriers}
Chapter \ref{sec:specifications} shows the size of the FM detectors \textit{SDB..SDD}. Due to the large diameter temperature based thermal stress needs to be minimized in order to prevent rising electronics noise due to detector deformation. This is an aspect which is hard to simulate due to the small, but in this domain significant inhomogeneity of the base material silicon. \acs{AHEPaM}'s design addresses this fact by selecting carrier material which \ac{CTE} is close to the one of silicon. Printed circuit board material \textit{Rogers AD1000} and ceramics \textit{$Al_{2}O_3$} and \textit{AlN} are currently under investigation. In order to show suitability of the final material we will use detector carriers made of this material in the DM.
\subsection{Mechanical and Structural design}
\label{sec:mech-design}
The main design driver of AHEPaM is the need to align all functional elements in a spatial context while respecting the design requirements of the various fields. \newline For the telescope the main focus is on the alignment of the particle detectors on a common middle axis and to position them laterally precisely in order to match with the results of the underlying \acs{GEANT4}-simulation (chapters \ref{sec:specifications} and Annex A)\\
For the \acs{EBox}, consisting of three the so called \textit{frames}, namely \textit{base-} (or pre amp-), \textit{filter-} and the \textit{back end}-frame, it's the arrangement and alignment of the electronics boards and their dedicated board-to-board connectors in order to provide good shielding between the analog and digital signal side and a short signal path on one hand. On the other hand to allow for good handling, integration and accessibility potential rework.\\
The \acs{EBox} is the main structural interface of the telescope and needs to support the high mass of the BGOs (1000g each). The main structural material used is in \acs{AHEPaM} is standard \textit{EN AW-6061} aluminium.
\subsubsection{Base Chassis}
\label{sec:chassis}
Two exceptions to the use of aluminium are the top frame of the EBox-chassis, called \textit{base-frame} and the feet. The latter will be produced from \textit{Grade 5}-titanium. If the base frame will be manufactured from titanium as well is still open and will be decided once the results of the thermal design become available. Titanium will be used in order to provide high mechanical strength and at the same time low thermal conductivity.\\
In order to withstand the high mechanical stress induced by the heavy BGOs under the mission-required dynamical loads, the chassis provides a relatively high sheet thickness of 3mm, increased to 7.5mm for the stiffening ribs. They reduce deformation of the plate to a minimum and provide sufficient material thickness for the threaded inserts. It is important to note the large weight-variation between the telescope elements: Both BGOs together will weigh 2000g, while two the Cherenkov detectors total 30g (without their chassis/ structure). Without proper stiffening and coupling of their masses, significant relative motion of these elements is expected, which, taking the small distances of the telescope arrangement into account, could lead to damage of the particle detectors. \\
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=0.75\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-fm_preamp-shaper.png}
\caption[]{\centering{Top view of the preamp and filter frames in assembled position.(Preamp boards in red, filter boards in green).}}
\label{fig:ahepam-fm-preamp-shaper}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-fm_backend.png}
\caption{\centering{Section view of the back end frame assembly.}}
\label{fig:ahepam-fm-backend}
\end{subfigure}
\caption{EBox's details.}
\label{fig:fm-ebox-details}
\end{figure}
The base chassis also acts as the \acs{EBox} for \acs{AHEPaM} (figure \ref{fig:ebox-board-stack}). Every chassis frame provides the mechanical interfaces for a dedicated set of \acp{PCB}, depending on its position. The top one (below the telescope) is the base- or preamp-frame. It accommodates the 4 identically shaped rectangular preamp-boards. It is very important for the performance of \acs{AHEPaM} to limit the distance between the detectors and the preamps. The detector wires are being fed through small grooves in the frame and directly soldered to the preamps below in order to eliminate the need for a connector, which might introduce unwanted noise into the signal chain. By that the preamps are already electrically shielded from the environment. The boards' grounding layers, the chassis and finally the instrument cover form a faraday cage for the optimal characteristics.\newline
The filter- or shaper-frame in the middle of the base chassis looks basically identical to the preamp-frame, since the shaper-boards have nearly the same geometry. That is necessary, because the instruments can be devided at this location in two halfs in order to give access to the preamp-boards for soldering. Since no hinge is foreseen, the integration process of \acs{AHEPaM} will require a dedicated handling fixture in order to support soldering and quality control activities. Due to its size an mass \acs{AHEPaM}'s design requires various dedicated handling and support provisions.\newline
The bottom or back end frame is quite massive (around 700g by the time of writing) due to comparatively large sheet thicknesses in order to support the high mass of the rest of the instrument, mounting interfaces for all four back end \acp{PCB} and the interface for the eight separate mounting feet, which are the interface to the S/C. The feet are attached to the chassis walls by bolts (taking the lateral forces) and centering pins (taking the shear forces) or good alignment with the S/C mounting interface.
\subsubsection{\acs{BGO}-Crystal Mounting}
\label{sec:bgo}
The \acs{BGO} readout works by detecting photons, which are emitted by the crystal atoms once a charged particle deposits enough energy in the lattice. In order to make sure that all light can enter the attached (glued) photo diodes, it needs to find its way into the detectors. This happens via uncontrolled reflections at the crystal surfaces until the photons interact with the photo diodes. To minimize signal loss during reflections, the \acs{BGO} is covered in \textit{Millipore} (a mixed cellulose ester membrane) and wrapped mit \textit{PTFE}-tape to hold it in place. By that photons are back scattered into the crystal.\newline
This wrapping turns the well defined crystal's geometric shape in an undefined state, because it's a manual process which hard to control parameters. Wrinkles and different overlaps add to varying layer thicknesses and radii around the crystal, making the overall geometry significantly less accurate.\newline
The mechanical support structure needs to compensate for that. It does so by using two aluminium shells which clamp the wrapped BGO in between. Small milled in features will define the final distance between the shells and by doing so limit the compression force implied on the crystal. Additional centering stones at the crystal's edges ensure an aligned assembly and will take residual rotational forces during vibration. This mechanical support has a long heritage in the work group (\textit{\acs{SO}, \acs{MSL}}) and matched well with the brittle material characteristic of the crystal.\newline
The chassis shells include milled in pockets to accommodate the mentioned read-out diodes, as well as one pre-amplifier board per detector in order to keep the distance at an absolute minimum and thus maintain a very high signal quality.\\
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=0.75\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-c9_bgo-sd-c-b-top.png}
\caption[]{\centering{Centering stones (red) align the wrapped BGO crystal and take potential residual rotational loads.}}
\label{fig:bgo-support}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-dm_pmt.png}
\caption{\centering{PMT interface. O-Rings (black) provide compliance to adapt to the glass surface and provide damping during vibrations.}}
\label{fig:pmt-support}
\end{subfigure}
\caption{AHEPaM's FM detector interface details.}
\label{fig:PMT_interface}
\end{figure}
\subsubsection{\acs{PMT}-Mounting}
\label{sec:pmt}
AHEPaM uses \acp{PMT} to read the Cherenkov detectors. The PMT has a glass body, which, as a characteristic, comes with large mechanical shape tolerances, especially for the cylindricity of the outer tube. On ground the \acs{PMT} is mechanically supported and electrically contacted via a dedicated socket. Under vibration load it need to be supported not only via its steel contacts, but along its glass enclosure in order to establish a load path there and not at the electrical contacts which could take damage. Thus it is supported by O-Rings, which allow for an easy integration, provide good form fit in order to establish a structurally rigid connection and finally act as compliance material which is able to compensate for the mentioned large tolerances. Since the \acs{PMT}s electrical contacts are rigid steel contacts encapsulated (molded) in glass, the soldering process is also subject to investigation.\newline
According to its data sheet, the \acs{PMT} (\textit{Hamamatsu R1924P-700}) comes with a cold storage temperature of -30$^{\circ}$C. Whether this temperature is a not-to-exceed threshold or can be exceeded is currently under investigation. In the scope of the first \acs{TMM} this is taken as the threshold temperature for the cold op/ non-op cases.
\subsubsection{Instrument Cover}
\label{sec:cover}
The instrument cover's main objective is to shield the detectors from light. Since \acs{AHEPaM}s detectors measure scintillation light already small amounts of stray light could lead to unwanted measuring errors. It is therefore a crucial requirement, that the telescope operates in a light tight surrounding. To make \acs{AHEPaM}s operation more independent from its surrounding light condition the telescope is shielded with a dome-like cover (figure \ref{fig:cover-w-plates}).\newline
This cover servers two purposes. The above mentioned light shielding and the electrical shielding against electronics noise.\\
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=0.75\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-dm_cover-w-plates.png}
\caption[]{\centering{\acs{AHEPaM}s top cover. The panels (green) act as shear plates to stiffen the structure.}}
\label{fig:cover-w-plates}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-dm_cover-wo-plates.png}
\caption{\centering{The filigree supporting frame in a preliminary, conceptual state.}}
\label{fig:cover-wo-plates}
\end{subfigure}
\caption{The instrument cover.}
\label{fig:cover-details}
\end{figure}
Its main design idea is to have a lightweight metal structure (figure \ref{fig:cover-details}) which provides receptacles (pockets) for installing sheet metal plates. These plates will act as shear panels, stiffening the whole structure to comply to the dynamic loads during vibrations.\newline
The details of the fabrications are currently under investigation, because a lightweight structure of this size is, taking conventional machining techniques into account, extremely demanding to produce.\newline
A candidate machining technique for such a structure is 3D-printing, but will require more detailing work of the here presented mechanical design.\\
First \acs{FEA} results show promising dynamic behaviour regarding random vibration.\\
Since the performance of the cover is very important, it is in the instrument team's own interest to early in the process test this element. Thus it's foreseen to include the cover in the \acs{DM} test campaign.
\subsection{Thermal Design}
\label{sec:therm-design}
The key aspect of \acs{AHEPaM}'s thermal design is to keep the detectors, more specifically its \acs{SSD}, cold during operation. The thermal design temperature for the hot-op case is $0^{\circ}C$. The interface temperature for this case is defined in \emph{R-AHEPaM-039} as 40$^{\circ}$C. Taking the above mentioned 0$^{\circ}$C design temperature into account, there is a $\Delta{T}$ of approx. 40K which needs to be established between the mounting interface of the chassis and the detectors.\\
A significant thermal design driver is the environment the instrument will operate in. Given the early state of the \acs{ATHENA} mission it is not surprising that important aspects of it are not yet defined. \newline Aspects like accommodation and radiative coupling on/ with the spacecraft, which will significantly influence the thermal behaviour, are not yet available to drive the setup of the thermal model. \newline
Therefore some assumptions have been made in order to fill in necessary information.\\
The intention of the \acs{TMM} is to study the thermal behaviour of \acs{AHEPaM} at the assumed worst case hot/ cold scenarios the instrument might later operate in. Therefore we defined solar radiation at 1 \acs{AU} as a global heat source. In order to balance the solar heat intake we introduced an external radiator into the model, as well as survival heating power. Whether our assumtions are compatible with a later \acs{ATHENA} mission needs to be thoroughly reviewed given the final requirements.\newline
The following chapters discuss the design aspects applied to the instrument model. Due to the early state of the mission, some of them are just virtual components, e.g. the external radiator and the accompanying thermal strap, which not yet have a CAD-model representation.\\
%At the moment the presented \acs{TMM} under \cite{ahepam-djf} provides a helpful initial working point for initially assessing \acs{AHEPaM}s thermal behaviour.\\
The initial thermal mathematical model, further discussed in \cite{ahepam-djf} baselines this approach.
\subsubsection{Thermal Interface}
\label{sec:therm-interface}
\acs{AHEPaM}'s design (figure \ref{fig:ahepam-with-cover}) shows the ebox-chassis with its eight mounting feet. They are the mechanical, as well as the thermal interface to the spacecraft (leaving harnesses out in the scope of this paragraph). The feet are built as separate components. By that the design can be adjusted if it becomes necessary without the need of rebuilding more costly parts.\newline
Also thermal verification (thermal cycling) can be sped up by using solid metal feet with low thermal resistance. The chosen design allows for adjusting the material, length and cross section of the feet, which are the main parameters that influence their thermal conductivity.
\subsubsection{Radiators vs. Radiating Surfaces}
\label{sec:radiators}
In order to get close to the above mentioned hot-op design temperature of 0$^{\circ}$C it is clear that the instrument needs to be able to radiate part of its dissipated heat away from the instrument. Since its cover provides large surface areas, it is logical to build these areas in a way, that they can radiate heat. This approach of course requires an unobstructed line of sight to space and thus prohibits the use of \acs{MLI}, at least in areas used as radiator. In case solar illuminations occurs, the radiating surface will be equipped with either \acs{SSM}-tape or \acs{OSR}-tiles in order to reduce solar absorption and to maximize IR emission. While this approach can work for the hot case (environment applies heat, instrument dissipates its nominal OP-power) it has to be balanced carefully for the cold case (reduced amount of heat from the environment, instrument is off and thus doesn't dissipate power). Because here, depending on how the instrument is aligned towards the sun, the full cover's area radiates heat.\newline This can quickly lead to exceeding the given cold temperature requirements for the \acs{PMT}.\\
%As a first step thermal modeling will need to determine the necessary required radiating area, assuming the hot operational case. It needs to be investigated whether separate radiators, e.g. connected by thermal straps and being located externally to the built volume or radiating areas, means instrument cover surfaces equipped with reflective elements like \acp{OSR} are more suitable for the final design.
In case external radiators will be used, thermal switches are known elements which might need to be considered in later iterations. A potential use will be carefully considered, because usually they come with a large size and mass constraint.
\subsubsection{MLI Insulation}
\label{sec:insulation}
As mentioned previously, MLI can not be used in cover areas used as radiators. Nevertheless if it becomes necessary to limit heat coupling with the spacecraft body, it can be used to cover all areas not being used as radiators, e.g. the \acs{EBox}' side walls, bottom plate and potentially certain areas of the cover.
\subsubsection{Thermal Barriers}
\label{sec:therm-barriers}
Another way to limit heat intake from the instrument through its interface is to adjust the heat flow in/ through the chassis by adjusting the material of some elements. \newline Since \textit{R-AHEPaM-041} sets the thermal interface temperature to $-40^{\circ}$C..$+40^{\circ}$C the feet will be built from titanium (please refer to \cite{dml} for materials' details), which has a significantly lower thermal conductivity and thus reduces the thermal coupling with the interface. \newline The same logic applies to the base-frame. The idea is to insulate the detectors from the \acs{EBox}, which acts as the heat source (no power is consumed in the telescope). By doing that a potential external radiator applied to the \acs{EBox} can in hot cases directly conduct heat away from it, while in the cold cases insulates the telescope and by that limits further cooling of the \acs{PMT}.
\subsubsection{Heating}
\label{sec:op-heating}
Depending on the outcome of the thermal modeling and the depending design process it might become necessary to apply external heating during operational phases to the unit.\newline
The main driver here is the amount of externally applied heat to the unit. As mentioned above, solar illumination or thermal radiation from the \acs{S/C} can be sources of that.\newline
In order to develop a thermally robust operational use-case for the instrument, the radiator area needs to be defined accordingly depending on the heat-intake the unit will be exposed to.\newline
That might lead to a case where due to the radiator size the unit gets too cold in the cold-op or cold non-op case and that it consequently needs to receive heating in order to prevent damage.\\
Regarding the stability/ robustness of the unit's performance there's a strong favour for operational heating. A passive design (no op-heating) implies the precise knowledge over time of the environmental parameters. A change, e.g. due to unforeseen direct sun illumination or indirect due to reflections, can not be accounted for.\\
As mentioned in \ref{sec:pmt} it is currently under investigation if the \acs{PMT} is allowed to get colder than -30$^{\circ}$C which currently is the minimum temperature threshold for the cold cases and has a big influence in order to determine if op-heating is necessary. An even greater influence has the accommodation of \acs{AHEPaM} on the \acs{S/C} as described earlier.\\
The instrument team understands the scope and subsequent outcome of the initial \acs{TMM} as a mandatory step of gaining basic knowledge of \acs{AHEPaM}s thermal behaviour and thus to drive the decision process of the final instrument design.
\newpage
\subsection{Electronics Design}
\label{sec:electronics-design}
\subsubsection{Instrument Block Diagram}
The AHEPaM EBox is separated into different sections placed on different boards.
The \acp{LVPS} gets the +28.0V and will provide all needed voltages for the unit including the bias voltages for the detectors but excluding the high voltage for the \acp{PMT}. This adjustable high voltage will be generated on an own \acp{HVPS} board. The digital board contains one \acp{FPGA}, \acp{RAM} and \acp{EEPROM} for configuration data and will do the data post processing and the communication interface. The analog board contains a \acp{FPGA} which controls 32 \acp{ADC}s with multiplexed input channels. Each ADC samples three sensor signals sequentially, which results in 96 channels. Most of them are shaped dual gain channels driven by one preamplifier.
\begin{figure}[h!]
\centering
\includegraphics[width=\textwidth]{cau-ath-ddc-0006_i1-0/media/20230613-AHEPaM-block-diagram-BLOCK-DIAGRAM.pdf}
\caption[Block Diagram]{Block Diagram of AHEPaM}
\end{figure}
\subsubsection{Signal Flow}
For the number of 96 detector signals the needed infrastructure of preamps, shapers, filters, linear regulators and the 32 ADCs are populated on two times of four PCBs, which fills around the full base area of the instrument.
The instruments is splitted into two segments. The upper segment contains the detector head with preamp PCB and filter ADC PBC. The lower segment contains the LVPS, HVPS, the digital PCB and the analog PCB. These two seqments will be interconnected during assembly with four NANO-D connector type jumper harnesses.
\begin{figure}[h]
\begin{subfigure}{0.5\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-ddc-0006_i1-0/media/20230613-AHEPaM-block-diagram-SENSOR.pdf}
\caption[Sensor Signals]{Sensor Signals of AHEPaM Detectorhead}
\end{subfigure}
% \hfill
\begin{subfigure}{0.5\linewidth}
\centering
\includegraphics[width=\textwidth]{cau-ath-ddc-0006_i1-0/media/nanod-dual-row-jumper.png}
\caption[Jumper Harness]{Jumper harness between the two segments}
\end{subfigure}
\caption{sensor signal details and section interconnection jumper harness}
\end{figure}
\begin{figure}[h!]
\centering
\includegraphics[width=\textwidth]{cau-ath-ddc-0006_i1-0/media/20230613-AHEPaM-block-diagram-SENSOR-PA-ADC-ANA-DIG-LVPS-HVPS.pdf}
\caption[Signal Flow]{Signal Flow of AHEPaM}
\end{figure}
\newpage
\textbf{\subsubsection{Power and Control Interface Definition}}
The instrument is designed for a primary bus power of +28V and control lines to switch instrument hard on and off.
\subsubsection{Data Interface Definition}
The instruments communication baseline to the space craft for DM and FM is a serial \acp{UART} over \acp{LVDS} connected to the digital FPGA. When ESA requires a MIL-STD-1553 interface for FM, an additional communication board will be added to fulfill this requirement.
\subsubsection{Register Description}
The measurement principle is to sample continuously the shaper signals which are the wider preamp signals. When a signal peak is detected which fulfil the set trigger level, the signal processing of all channels is started.
On Solar Orbiter we expect high trigger rates, with fast shaping times and more digital filtering and fully parallel digital processing. The employed flight part adc128s102 has eight multiplexed inputs. On Solar Orbiter seven of the inputs remain unused.
For AHEPaM we propose to use three inputs for detector input and five channels are available for housekeeping. To achieve the necessary resolution we add two more poles to the analog filter in form of a Sallen-Key low pass. The digital processing will be pipelined though a single processor chain for all detector units.
This was concept is already developed in cooperation for the french Dorn instrument on the Chinese Mission Chang’E 6 and is described in detail in the separate document \href{https://cloud.rz.uni-kiel.de/index.php/s/YAWWZRRYrrS7Kg3}{Dorn Signal Processing}.
% https://cloud.rz.uni-kiel.de/index.php/s/egKwPnMs8K4NXe6
\newpage

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\section{Performance analysis}
\label{sec:performance-analysis}
\graphicspath {{../cau-ath-djf-0007_i1-0/media/figs_sim}}
The performance of AHEPaM was analysed using a GEANT4 simulation. Based on the analysis above we have decided that \textbf{a Cherenkov is recommended in order to fulfill the requirements}. Furthermore, the performance analysis for protons and electrons have been done with a high-accuracy and a high-statistics data product for both species. \ac{AHEPaM} will be able to produce all these data products simultaneously. The design philosophy behind these data product is as follows:
\begin{itemize}
\item The high-accuracy data products limit the opening angle by requiring all detectors to be hit by a particle. This reduces the geometric factor leading to lower statistics compared to the high-statistics channels. The benefit, however, is a reduced contamination (i.e. less protons in the electron channel) leading to lower systematic uncertainties.
\item The high-statistics data products do not require all detectors to be hit, improving the opening angle and thus the statistics on the cost of a higher contamination (i.e. the Cherenkov detectors can not be utilized since they are missed by particles with oblique trajectories).
\end{itemize}
Since these data products will be produced in parallel, the high-statistics data products can be used to monitor temporal variations over a time period of interest. If no variations are observed, this information allows the usage of the high-accuracy mode in that given time period by accumulating statistics over that given time period.\newline
In addition, measurements over a prolonged time period can be utilized to validate and/or improve the high-statistics channel by comparing the fluxes to the high-accuracy mode. This is especially important for the electron measurements due to the proton contamination. This contamination will be corrected for by using the measured proton spectrum and the simulated response (i.e. the likely-hood of a proton to end up in the electron channel) in order to estimate the number of protons in the electron channels and subtract this from the measured electron channel count rate. A detailed mathematical description of the systematic uncertainties introduced by this method is given in section \ref{sec:error_estimation_eq}.\newline
The derived uncertainties for the protons and electrons in their corresponding high-accuracy and high-statistics data products are summarized below. Note that while the proton uncertainty is derived from the expected counting statistics, the electron uncertainties also include the systematic uncertainties caused by proton contamination.
\subsubsection*{High-accuracy proton channels}
It has been shown that requiring a coincidence from SDA up to SDE for protons allows for utilizing the Cherenkov in order to separate at 2~GeV. Using this coincidence, protons from 150~MeV up to 2~GeV can be detected in
\begin{itemize}
\item five channels on 10ks time resolution with 2.7\% stat. uncertainty
\item two channels on 3ks time resolution with 3.1\% stat. uncertainty
\end{itemize}
This would also provide an integral channel for protons above 2~GeV.
Note that the protons up to 150~MeV can also improve the statistics utilizing the stopping channels. \newline
\subsubsection*{High-statistic proton channels}
In addition, it is possible to enhance statistics by only requiring the detectors SDB to SDD to be hit (with the disadvantage that no Cherenkov signal is ensured). This would result in
\begin{itemize}
\item five channels on 10ks time resolution with 1.2\% stat. uncertainty
\item two channels on 3ks time resolution with 1.4\% stat. uncertainty
\end{itemize}
\textbf{Note that the instruments hard- and software can be designed such that both, the detailed and high statistic proton analysis are performed in parallel.} %An additional study with coincidences neglecting SDA and SDE entirely (i.e. SDB to SDD are triggered) is currently ongoing and we expect such coincidence to further increase statistics for the high statistic proton channel.
\newline
\subsubsection*{High-accuracy electron channels}
Regarding electrons we have found that
\begin{itemize}
\item two channels on 50ks (13 hours) time resolution with 5.5\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\item two channels on 100ks (1 day) time resolution with 3.9\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\item five channels on 100ks (1 day) time resolution with 6.1\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\item five channels on 500ks (5 days) time resolution with 2.8\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\end{itemize}
Furthermore, no large flux variation at these energies are expected for electrons on short time scales.\newline
Note that the electrons up to 200~MeV can also improve the statistics utilizing the stopping channels.
\subsubsection*{High-statistic electron channels}
Similar to the high statistic proton channel, it is possible to enhance statistics by neglecting the outer rings of SDB-SDD as veto-counter. This leads to
\begin{itemize}
\item two channels on 50ks (13 hours) time resolution with 3.5\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\item two channels on 100ks (1 day) time resolution with 2.5\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\item five channels on 50ks (13 hours) time resolution with 5.5\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\item five channels on 100ks (1 day) time resolution with 3.9\% uncertainty (including both the statistical as well as the systematical uncertainty due to proton contamination)
\end{itemize}
\textbf{Note that the instruments hard- and software can be designed such that both, the detailed and high statistic electron analysis are performed in parallel.}

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\section{Detector and Telescope Specifications}
\label{sec:specifications}
As described previously in order to limit project cost to a reasonable minimum stock or residual parts have been specified for the \acs{DM}. This chapter shows the detector and telescope specifications of the two statuses and allows for a comparison of the two.
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/cau-ath-icd-0009_i2-0_telescope.pdf}
\caption[FM telescope]{\centering{\acs{FM} telescope}}
\label{fig:techdraw-fm-telescope}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/cau-ath-icd-nnnn_i1-0_telescope.pdf}
\caption[DM telescope]{\centering{\acs{DM} telescope}}
\label{fig:techdraw-dm-telescope}
\end{subfigure}
\caption[Two side by side pages showing the FM and DM telescope]{Details of the FM/ DM telescopes.}
\label{fig:telescope-specs}
\end{figure}
\begin{figure}[h]
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/cau-ath-icd-0009_i2-0_detectors.pdf}
\caption[FM detectors]{\centering{\acs{FM} detectors}}
\label{fig:techdraw-fm-detectors}
\end{subfigure}
\hfill
\begin{subfigure}[]{0.5\linewidth}
\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/cau-ath-icd-nnnn_i1-0_detectors.pdf}
\caption[DM detectors]{\centering{\acs{DM} detectors}}
\label{fig:techdraw-dm-detectors}
\end{subfigure}
\caption[Two side by side pages showing the FM and DM telescope]{Details of the FM/ DM telescopes.}
\label{fig:detector-specs}
\end{figure}
%\subsection{Specification Tree}
%\begin{figure}[h]
% \centering
% \includegraphics[width=0.8\linewidth]{media/ahepam_spec-tree.pdf}
% \caption[ahepam-dm-spec-tree]{\_\_DRAFT\_\_ AHEPaM Specification Tree \_\_DRAFT\_\_}
% \label{fig:spec_tree}
%\end{figure}