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\section{The Silicon Strip Tracker Layout} |
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\label{sec:Layout} |
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The CMS SST |
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instruments the radial range between 20~cm and 116~cm and $|\eta| < 2.5$ around the |
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LHC interaction point. |
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The central region ($|z| < 118$ cm |
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\footnote{A CMS coordinate system, used through this note, is defined in such a way that |
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$z$ is the coordinate along the LHC beam axis, $y$ is the vertical direction and $x$ |
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complete the system; the origin being the nominal beam interaction point.}) |
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is split into an Inner Barrel (TIB), made of four detector layers, and an |
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Outer Barrel (TOB), made of six detector layers. The TIB is shorter than the TOB, and is |
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complemented |
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by three Inner Disks per side (TID), each Disk being in turn composed of three |
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Rings. The forward and backward regions |
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(124~cm $ < |z| < $282~cm) are covered by nine Endcap (TEC) disks per side, each one made of |
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up to seven rings. |
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The two innermost layers of both TIB and TOB as well as rings number one, two and five |
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of TEC and one and two of TID are instrumented with double-sided detector modules. |
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A complete description of the Silicon Tracker layout (Fig.\ref{fig:layout}) |
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can be found elsewhere~\cite{ref:layout}.\\ |
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\section{TIB and TID layout} |
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TIB and TID are very compact objects with high readout granularity; |
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channel and module densities are three to four times larger than in |
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the other SST subsystems as shown in Table~\ref{table:Density} where |
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the main parameters of the SST subsystems are |
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reported. |
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The TIB and TID layout has been designed keeping in mind their complexity: |
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the mechanical structures have been simplified as much as possible, |
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while the routing of the services (cooling, readout, controls) has been |
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adapted to the very high channel density making use of all accessible |
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paths inside the detector. |
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|
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%matching the |
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%following features: simple mechanical structure; easy routing of the |
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%large number of service connections (cooling, readout, controls); easy |
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%component mounting in the case of the TIB non-planar (cylindrical) |
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%geometry; optimization the theta (and phi?) for the TID. |
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|
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The TIB is structured in four concentric layers. Each layer is |
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split along the vertical plane at $z=0$ into two almost identical half-layers. Each |
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half-layer is further split along the horizontal at $y=0$ into two semi-cylindrical |
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structures, also referred to as ``shells''. |
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Both spilts in $\phi$ and $z$ are done ins such a way that the sensor surfaces always |
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overlap leaving no dead area when measuring high momentum charged particles coming |
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from the interaction region. |
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The shell structure is a |
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semi-cylindrical carbon fiber assembly strenghten by two circular |
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flanges at both ends. To decrease their density and to provide a better accessibility |
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during integration, modules and services are hold |
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either on the external and the internal surfaces. The services are laid down on |
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the surface and run parallel to the $z$ axis. |
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% on the surface toward the end (i.e. in the |
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%direction along which $|z|$ increases). |
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The modules and the related |
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services that sit on the same side of a shell at the same $\phi$ |
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coordinate constitute a \textit{string}. |
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|
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The TID is split into six disks (three per each side of |
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TIB). The disk is made up by three sub-disks called "rings" since each |
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ring holds modules at the same radius. The ring structure consists of |
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a mechanical support made of an annular carbon fiber honeycomb. |
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Also in this case modules and services are located on both sides |
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of the mechanical structure. |
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%to decrease the density |
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%and therefore providing a better accessibility during ring integration |
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%and disk assembly. |
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|
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The TIB/TID system is physically |
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divided into two separated structures, one located in the |
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$z > 0$ region and one located in the $z < 0$ region and known as |
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TIB/TID+ and TIB/TID- respectively. Each TID+ and TID- is obtained by |
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inserting, positioning and fixing the three disks into a carbon fiber |
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cylinder called {\it Service Cylinder}. Each Service Cylinder has |
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several holes at the disk positions; this allow the |
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connection of the power lines and to route out all the fibers of the |
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disk. The Service Cylinder is also used to connect mechanically TIB+/- |
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and TID+/-, and to route out the services of the TIB and of the TID. |
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|
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The cooling in the TIB/TID is distributed via aluminum pipe circuits |
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that are bent into loops and soldered to inlet/outlet manifolds at |
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the flange for the TIB, and at the ring outer edge for the TID. |
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The thermal connection between pipes and sensor modules is made with Aluminum ledges which are |
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precisely glued on the carbon fiber support structure and in good thermal contact with the pipes. |
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On each ledge there are two threaded M1 holes onto which the modules are tightened. |
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Precisely drilled slots, coaxial with the threaded holes, are the reference point where |
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insets are stick in providing mechanical reference for modules. An example for a TIB module |
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is shown in Fig.~\ref{fig:module_cooling}). |
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|
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The TIB and TID substructures, 16 shells and 18 rings, are relatively |
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large-sized objects: one shell holds 135 to 216 modules, one ring holds 40 to 48 modules. |
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Some other relevant specifications of the TIB and TID substructures are |
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summarized in Table~\ref{table:layers}. |
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A finished half of the TIB and a TID Disk are shown in |
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Fig.~\ref{fig:tibtid}. The pictures allow the sub-structures to be |
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recognized. |
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|
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|
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|
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\begin{figure}[!htb] |
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\begin{center} |
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\includegraphics[width=0.45\textwidth]{Figs/shell.pdf} |
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% \includegraphics[height=0.5\textwidth]{Figs/TIB-assembled.pdf} |
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\hskip 1cm |
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\includegraphics[width=0.45\textwidth]{Figs/TIB_barrel.png} |
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\end{center} |
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\caption{A L3 TIB shell (left panel) and half of TIB assembled (right panel).} |
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\label{fig:tib} % Give a unique label |
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\end{figure} |
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|
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\begin{figure}[!htb] |
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\begin{center} |
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\includegraphics[width=0.85\textwidth]{Figs/rz.pdf} |
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\includegraphics[height=0.35\textwidth]{Figs/ring.pdf} |
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% \includegraphics[height=0.5\textwidth]{Figs/TIB-assembled.pdf} |
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\hskip 3cm |
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\includegraphics[height=0.35\textwidth]{Figs/TID-disk.pdf} |
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\end{center} |
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\caption{Longitudinal cross section of one quarter of the CMS SST. |
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Thicker (blue) segments indicate double-sided silicon microstrip modules. |
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The nominal beam interaction point is located in (0,0), dimensions are in mm. |
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The pseudorapidity ($\eta$) coverage is also shown.} |
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\label{fig:layout} % Give a unique label |
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\caption{A TID ring 1 assembled (left panel) and one complete TID disk (right panel).} |
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\label{fig:tid} % Give a unique label |
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\end{figure} |
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The whole tracker region is embedded into the CMS 4~Tesla solenoidal magnetic field. |
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Charged particle transverse momentum resolution of about 1.5\% for centrally-produced |
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muon of 100~GeV/$c$ is expected~\cite{ref:ptdr}. \\ |
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From the detector construction point of view it is important to note that the TIB/TID |
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system is divided into two physically separated structures: TIB/TID+, which is located in the |
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$|z| > 0$ region and TIB/TID-, located in the $|z| < 0$.\\ |
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The entire tracker is inserted in a carbon fiber Support Tube which is attached to |
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the Electromagnetic Calorimeter and insulated by the rest of the experiment by a |
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'Thermal Shield'. |
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|
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\begin{table}[!htb] |
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\begin{center} |
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%\begin{tabular}{|l||c|c|c|c|c|c|c|} |
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\caption[smallcaption]{Total number of modules, strips (or electronic readout channels), detector volume and |
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channel density for the different tracker subsystems. Service access area is also defined |
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for barrel geometry detectors (TIB and TOB) as their flange area. The channel density in this |
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area gives also an idea of the complexity of the detector integration.} |
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\label{table:Density} |
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\begin{tabular}{|l|ccccccc|} |
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\hline |
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& & & & Module & Channel & Service & Service \\ |
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& \# of &\# of & Volume & Density & Density & Area & Density \\ |
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& modules & channels & [m$^3$]& [$\times 10^3$ m$^{-3}$] & [$\times 10^6$ ch m$^{-3}$] & [m$^2$] & [$\times 10^6$ ch m$^{-2}$]\\ |
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%\hline |
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\hline |
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TIB & 2724 & 1 787 904 & 0.82 & 3.2 & 2.2 & 1.6 & 1.11\\ |
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%\hline |
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TID & 816 & 565 248 & 0.5 & 1.6 & 1.1 & & \\ |
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%\hline |
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TOB & 5208 & 3 096 576 & 5.9 & 0.89 & 0.52 & 5.7 & 0.54\\ |
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%\hline |
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TEC & 6400 & 3 866 624 & 11 & 0.58 & 0.35 & & \\ |
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\hline |
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\end{tabular} |
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\end{center} |
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\end{table} |
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|
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|
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\begin{table}[!htb] |
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\begin{center} |
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\caption[smallcaption]{Details on the different layers/rings of the TIB/TID. } |
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\label{table:layers} |
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%\begin{tabular}{|l||c|c|c|c|c|c|c|} |
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\begin{tabular}{|l|ccccccc|} |
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\hline |
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Layer & \# mechanical & \# cooling & DS/SS & \# of modules & \# of channels & \# Control & \# Mother \\ |
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& structures & circuits & layer & total & per module & Rings & Cables \\ |
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\hline |
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% \hline |
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TIB L1 & 4 shells & 12 & DS & 672 & 768 & 24 & 112 \\ |
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TIB L2 & 4 shells & 16 & DS & 864 & 768 & 32 & 144 \\ |
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TIB L3 & 4 shells & 12 & SS & 540 & 512 & 12 & 180 \\ |
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TIB L4 & 4 shells & 16 & SS & 648 & 512 & 16 & 216 \\ |
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TID R1 & 6 rings & 24 & DS & 288 & 768 & 12 & 48 \\ |
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TID R2 & 6 rings & 24 & DS & 288 & 768 & 12 & 48 \\ |
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TID R3 & 6 rings & 24 & SS & 240 & 512 & 12 & 48 \\ |
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\hline |
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\end{tabular} |
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\end{center} |
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\end{table} |
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|
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|
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%\subsection{Mechanical Structures} |
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|
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%A TIB shell is shown on Fig.~\ref{fig:tibshell}). |
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|
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%Each cooling loop hosts three modules placed in a straight row, which is called a |
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%A string of modules is connected to the same CCU, thus forming a control branch. |
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|
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%\begin{figure} |
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%\centering |
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%\includegraphics[width=\textwidth]{ } |
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%\caption{TIB shell: are visible the internal and external parts, the cooling pipes and the string} |
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%\label{fig:tibshell} |
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%\end{figure} |
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|
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|
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%\begin{figure} |
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%\centering |
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%\includegraphics[width=\textwidth]{ } |
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%\caption{TID ring } |
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%\label{fig:tidring} |
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%\end{figure} |
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|
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|
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|
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\begin{figure} |
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\centering |
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\includegraphics[width=0.6\textwidth]{Figs/module_cooling.pdf} |
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\caption{Module Cooling. |
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\textbf{Upper picture:} part of a cooling loop with six ledges to hold three modules and three |
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smaller ledges to hold Analog Opto-Hybrids (adjacent cooling circuits are partially visible). |
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\textbf{Lower picture:} a detail of a cooling loop. The cooling fluid direction |
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is evidenced with blue arrows, and the precision holes for module insertion are circled in |
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red. A module mounted on the nearby position is also visible.} |
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\label{fig:module_cooling} |
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\end{figure} |
