\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.\\


\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 (yellow boxes in figure \ref{fig:fm-telescope-if-details}). 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}.
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