\section{Differences between FM and DM design.}
\label{sec:differences}
This chapter gives an overview over the known\footnote{by the time of writing} differences between the two design statuses.

However, it is important to understand the high level of comparability between the two designs.\\ Identical items/ sub-assemblies between DM- and FM-status are:

\begin{itemize}
    \item The chassis regarding its outer dimensions and material. Consequently the mass is as well, except for potential adaptations to give excess to the external control electronics (connector cutouts). This is expected to be in the lower ten grams range.
    \item Instrument cover.
    \item The \acs{BGO} sub-assembly, as well as its mounting.
    \item The wiring from the telescope's readout detector to the preamps.
    \item The \acs{CHKV} sub-assembly, except for its attached particle detector.
    \item The \acs{PMT} and it's electronics.
    \item The instrument feet (mechanical interface).
\end{itemize}

In general the instrument team is dedicated to build the DM as flight-like as possible. Nevertheless unforeseen circumstances might make it necessary to apply some adaptations. In this case all changes will be recorded and reported in the relevant test documentation. 

\subsection{Detectors}
\label{sec:detector-diffs}
One of the main differences compared to chapter \ref{sec:basic-design} are the different types of particle detectors the telescope consist of. Comparing figure \ref{fig:fm-telescope-wo-readout} and figures \ref{fig:dm-telescope-wo-readout}, the significant size difference between the conceptual FM- and the specified DM-\acp{SSD} can be seen.\\



\begin{figure}[h!]
	\begin{subfigure}[]{0.5\linewidth}
		\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-dm_top_telescope.png}
		\caption[]{\centering{The telescope's particle detectors. (Transparency for better visualization.)}}
		\label{fig:dm-telescope-wo-readout}
	\end{subfigure}
	\hfill
	\begin{subfigure}[]{0.5\linewidth}
		\includegraphics[width=\linewidth]{cau-ath-ddc-0006_i1-0/media/ahepam-dm_top_telescope-w-dets.png}
		\caption{\centering{The telescope with the accompanying readout detectors.}}
		\label{fig:dm-telescope-w-readout}
	\end{subfigure}
	\caption{AHEPaM's DM-telescope.}
	\label{fig:dm-telescope}
\end{figure}

The reduced size significantly reduces costs of the DM while still allowing a test setup that can proof the measurement capabilities derived in \cite{ahepam-djf}. Both, the showering of high energy electrons in the \acp{BGO} and the identification of relativistic particles using the Cherenkov detector can be tested using a beam of particles that does not require large \acp{SSD}. The structural properties of the large FM \acp{SSD} will, however, be tested using a simple silicon shard with the dimensions of the FM \acp{SSD}.\\

Table \ref{tab:detector-diffs} compares the details of the DM- and FM-detectors.

\begin{table}[h!]
\centering
\caption{Detector FM/ DM design differences.}
\label{tab:detector-diffs}
\begin{tabular}{lll}
\hline
                          & \multicolumn{1}{c}{\textit{\textbf{FM}}} & \multicolumn{1}{c}{\textit{\textbf{DM}}}                                     \\ \hline
\textit{Detector variety} & 3 new designs                            & \begin{tabular}[c]{@{}l@{}}2 stock designs\\ (heritiga SO/ HET)\end{tabular} \\ \hline
\textit{Channel count}    & 4                                        & \begin{tabular}[c]{@{}l@{}}2 (HET-A),\\ 3 (HET-B)\end{tabular}               \\ \hline
\textit{Segmentation}     & yes                                      & no                                                                           \\ \hline
\textit{Si thickness}     & 0,5mm                                    & 0,3mm                                                                        \\ \hline
\textit{\begin{tabular}[c]{@{}l@{}}Size (Outer\\ Channel Diam.)\end{tabular}} &
  \begin{tabular}[c]{@{}l@{}}59 ('inner'),\\ 60 ('outer-small'),\\ 120 ('outer-large')\end{tabular} &
  \begin{tabular}[c]{@{}l@{}}18,04 (HET-A),\\ 37,13 (HET-B)\end{tabular} \\ \hline
\end{tabular}
\end{table}



\subsection{Telescope}
\label{sec:telescope-diffs}

The telescope design and geometry is tailored to the FM detectors and their carrier geometry. In order to mount the \textit{\acl{SO}}-stock detectors via mechanical adaptors, different M1,6-bolts need to be used. These consume more space than the original FM-detector mounting and need thus to be slightly shifted around their optimal FM-position between the \acs{BGO} and \acs{CHKV}, which results in an uneven positioning compared to the FM.
However, as mentioned in section \ref{sec:detector-diffs}, the size and position of the \acp{SSD} are not relevant for testing purposes due to the fact that the measurement capabilities will be tested on a beam line.

\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}



\subsection{Electronics}
The fully equipped FM will have 48 sensor signals where each signal has its own preamp and in the majority of cases two shapers for dual gain. The preamps are separated on four preamp PCBs with their shaper and ADCs PCB below and will be read out with 32 ADCs there in sum, where each ADC has multiplexed inputs.

For DM the sensor head signals are distributed to two not fully populated preamp PCB and their shaper and ADC PBC below — also not fully populated. This two ADC PCBs are connected with NANOD jumper cables with a dummy ANA PCB to demonstrate the assembly of the two main segments sensor head and electronic box.

The electronic box in DM has a dummy ANA PCB only — no LVPS-, HVPS- and DIG PCB. The DM has one connection fed through chassis opening from dummy ANA PCB to lab readout electronic for signal processing outside from the instrument. The lab electronic has a 18 channel readout electronic for demonstration.


\begin{figure}[h]
	\centering
	\includegraphics[width=1.0\linewidth]{cau-ath-ddc-0006_i1-0/media/irena.pdf}
	\caption[]{IRENA lab readout electronic has 18 input channels}
	\label{fig:IRENA}
\end{figure}