\setlength{\titleblockheight}{35mm}
\begin{document}
-\title{The CBM-MVD: the PRESTO project\thanks{This work has been supported by BMBF (05P12RFFC7), EU-FP7 HadronPhysics3, HGS-HIRe, GSI and HIC for FAIR.}}
+\title{PRESTO: PREcursor of Station TwO of the CBM-MVD\thanks{This work has been supported by BMBF (05P12RFFC7), EU-FP7 HadronPhysics3, HGS-HIRe, GSI and HIC for FAIR.}}
\author[]{M. Koziel}
\author[]{T. Tischler}
%\section{Sensor integration}
-The PREcursor of Station TwO (PRESTO) project of the CBM-MVD addresses the double-sided integration of $15$ MIMOSA-$26$ sensors (dummies and working sensors) onto a $8 \times 8~\text{cm}^{2}$ CVD diamond carrier \cite{CVD} featuring a thickness of $150~\upmu$m. The PRESTO module will employ the new flex cables \cite{FPC} providing all signals needed to operate and read out the sensors, see sketch \ref{fig:presto_sketch}.\\
-To assembly this module, new sensor positioning jigs aiming for a sensor positioning precision with respect to the support and the neighboring sensors of below $100~\upmu$m were manufactured. To evaluate the integration concept, the RAL-$247$ adhesive and the new jigs, a dummy PRESTO module based on $200~\upmu$m glass plate was selected to server as sensor carrier, employing $50~\upmu$m MIMOSA-$26$ dummies, see fig.~\ref{fig:presto_dummy}.\\
-The number of air bubbles introduced into the glue during its mixing process has been significantly reduced by degassing it in an exicator at about $4\cdot 10^{-1}$~mbar for about $1$ hour. However, this did not prevent the air bubbles to appear after the gluing of the sensors onto the carrier. The introduced air bubbles featured a size of about $100-300~\upmu$m diameter. To verify their impact on the $50~\upmu$ thin sensor dummies, the cured module has been placed inside a small vacuum chamber which has been evacuated for about $48$ hours to a value of $4\cdot 10^{-1}$~mbar. The visual inspection of the sensors using a high precision microscope did not reveal any mechanical damage. Further studies will be addressed with working sensors to check on-fly any possible correlation between sensor performance, pressure and bubble sizes.\\
-The gluing of the dummy sensors onto the glass carrier demonstrated that a glue volume of $3-5~\upmu$l is sufficient to dispense a uniform and thin (about $30~\upmu$m) layer underneath the sensors.\\
+The PREcursor of Station TwO (PRESTO) project of the CBM-MVD addresses the double-sided integration of $15$ MIMOSA-$26$ sensors (dummies and working sensors, $9$ of these on the front in a $3\times3$ and $6$ sensors on the back in a $2 \times 3$ arrangement) onto a $8 \times 8~\text{cm}^{2}$ CVD diamond carrier \cite{CVD} featuring a thickness of $150~\upmu$m. The PRESTO module will employ the new flex cables \cite{FPC} providing all signals needed to operate and read out the sensors, see sketch \ref{fig:presto_sketch}. In total, $10$ FPCs are required to read out these sensors.\\
+To assembly this module, new sensor positioning jigs aiming for a sensor positioning precision with respect to the support and the neighboring sensors of below $100~\upmu$m were manufactured. To evaluate the integration concept, the RAL-$247$ adhesive \cite{glue} and the new jigs, a dummy PRESTO module based on $200~\upmu$m glass plate was selected to server as sensor carrier, employing $50~\upmu$m MIMOSA-$26$ dummies, see fig.~\ref{fig:presto_dummy}.\\
+The number of air bubbles introduced into the glue during its mixing process has been significantly reduced by degassing it in an exicator at about $4\cdot 10^{-1}$~mbar for about $1$ hour. However, this did not prevent the air bubbles to appear after the gluing of the sensors onto the carrier. The introduced air bubbles featured a size of about $100-300~\upmu$m diameter. To verify their impact on the $50~\upmu$m thin sensor dummies, the cured module has been placed inside a small vacuum chamber which has been evacuated for about $48$ hours to a value of $4\cdot 10^{-1}$~mbar. The visual inspection of the sensor dummies using a high precision microscope did not reveal any mechanical damage. Further studies will be addressed with working sensors to check on-fly any possible correlation between sensor performance, pressure and bubble sizes.\\
+The gluing of the dummy sensors onto the glass carrier demonstrated that a glue volume of $3-5~\upmu$l\textemdash a different glue volume has been used for each row of sensors\textemdash is sufficient to dispense a uniform and thin (about $30~\upmu$m) layer underneath the sensors.\\
The horizontal sensor-to-sensor distances were measured to be below $5~\upmu$m. The vertical shifts between the sensors were measured to be of about $20~\upmu$m. The achieved precision is significantly below the envisioned one. Next steps comprise the establishing of procedures for the integration of the flex cables, the exercise of double-sided bonding and the verification of the vacuum compatibility.
\begin{figure}[htb]
\centering
-\includegraphics*[width=55mm]{PRESTO_sketch.png}
+\includegraphics*[width=60mm]{PRESTO_sketch.png}
\caption{Sketch of the arrangement of the sensors and the FPCs with respect to the support carrier within the PRESTO module.}
\label{fig:presto_sketch}
\end{figure}
Diamond Materials GmbH, Germany
\bibitem{FPC}
-P. Klaus et al., GSI annual report 2014.
+P. Klaus et al., "Ultra-low material budget Cu flex cable for the CBM-MVD. "GSI annual report 2014.
\bibitem{glue}
Private communication, Simon Canfer Rutherford Appleton Laboratory, Composites and Materials Testing Group, UK.
\maketitle
-This report summarizes the activities undertaken towards the construction of the Micro Vertex Detector (MVD) of the Compressed Baryonic Matter (CBM) experiment.
+This report summarizes the activities undertaken towards the construction of the Micro Vertex Detector (MVD) of the Compressed Baryonic Matter (CBM) experiment.
%\section{Sensor integration}
\section{Quality assurance}
+%\textbf{Quality assurance:$\;\;$}
The concept of quality assurance for the ultra-thin sensors to be integrated into the MVD has been discussed in \cite{QA}. Since the final sensors for the MVD do not exist yet, $18$ MIMOSA-$26$ AHR sensors thinned to 50 $\upmu$m were used to establish the required test procedures. The number of sensors which passed the tests has been compared with the know yields after thinning \cite{LG}. $12$ sensors were found without a significant number of dead/noisy pixels; they were qualified as fully operational. Four sensors exhibiting some dead rows/columns were marked as faulty. The two remaining sensors were not operational due to a power supply short (one sensor) and problems while powering one out of the four MIMOSA-$26$ sub-matrices. It was concluded that the observed yield is in agreement with the expectations.
\section{Development of an appropiate glue}
-An "ideal" adhesive for the integration of the sensors onto their supports should be easy to dispense in a thin and uniform layer\textemdash calling for a low viscosity\textemdash, radiation hard as well as elastic within the temperature range foreseen for the operation of the MVD sensors. Since there are none "on-shelf" products that meet these requirements, a custom-made, two compound adhesive with a working name RAL-$247$ was manufactured at the Rutherford Appleton Laboratory (RAL), Composites and Materials Testing Group, UK. The glue features a glass temperature of -$45~^{\circ}$C, a viscosity of below $100$ mPa$\cdot$s and a curing time of $48$ h at +$50~^{\circ}$C. To investigate its radiation hardness, RAL-$247$ samples were irradiated with X-rays to 100~Mrad and to a proton dose of about 10$^{15}$~n$_{eq}$/cm~$^{2}$. The irradiated samples were sent to RAL for further Dynamic Mechanical Analysis tests which unraveled a very similar performance of glue samples before and after irradiation \cite{glue}.
+%\textbf{Development of an appropiate glue:$\;\;$}
+An "ideal" adhesive for the integration of the sensors onto their supports should be easy to dispense in a thin and uniform layer\textemdash calling for a low viscosity\textemdash, radiation hard as well as elastic within the temperature range foreseen for the operation of the MVD sensors. Since there are none "on-shelf" products that meet these requirements, a custom-made, two compound adhesive with a working name RAL-$247$ was manufactured at the Rutherford Appleton Laboratory (RAL), Composites and Materials Testing Group, UK. The glue features a glass temperature of -$45~^{\circ}$C, a viscosity of below $100$ mPa$\cdot$s and a curing time of $48$ h at +$50~^{\circ}$C. To investigate its radiation hardness, RAL-$247$ samples were irradiated with X-rays to 100~Mrad and to a proton dose of about 10$^{15}$~n$_{eq}$/cm~$^{2}$. The irradiated samples were sent to RAL for further Dynamic Mechanical Analysis tests which unraveled a very similar performance of glue samples before/after irradiation \cite{glue}, see figure \ref{fig:picture}.
\section{Development of the heat sinks for the MVD}
-The operation of the MVD in vacuum requires a continuous cooling of the sensors to limit radiation induced defects as well as noise. To keep the material budget of the individual MVD station as low as possible, the cooling approach of the MVD employs highly thermal conductive sensor support materials (CVD diamond \cite{CVD} and encapsulated graphite) in the acceptance of the MVD and actively cooled aluminum-based heat sinks outside of this area. To evaluate the cooling concept and its vacuum compatibility, half-station heat sinks of the first three MVD stations were manufactured. The heat sinks incorporate a buried cooling pipe and have thermally been simulated prior their manufacturing using a worst case scenario for the sensor power dissipation plus an additional safety factor of four. These heat sinks are currently being evaluated under laboratory conditions focusing on their vacuum compatibility. The heat dissipation of the MVD sensors is provided by electric heaters.
+%\textbf{Development of the heat sinks for the MVD:$\;\;$}
+The operation of the MVD in vacuum requires a continuous cooling of the sensors to limit radiation induced defects as well as noise. To keep the material budget of the individual MVD station as low as possible, the cooling approach of the MVD employs highly thermal conductive sensor support materials (CVD diamond \cite{CVD} and encapsulated graphite) in the acceptance of the MVD and actively cooled aluminum-based heat sinks outside of this area. To evaluate the cooling concept and its vacuum compatibility, half-station heat sinks of the first three MVD stations were manufactured. The heat sinks incorporate a buried cooling pipe and have thermally been simulated prior their manufacturing using a worst case scenario for the sensor power dissipation plus an additional safety factor of four. These heat sinks are currently being evaluated under laboratory conditions focusing on their vacuum compatibility \cite{vacuum}. The heat dissipation of the MVD sensors is provided by electric heaters.
-\section{PRESTO}
-The PREcursor of Station TwO (PRESTO) project of the CBM-MVD addresses the double-sided integration of $15$ MIMOSA-$26$ sensors (dummies and working sensors) onto a CVD diamond carrier featuring a thickness of $150~\upmu$m. The project will be discussed in detail in a separate report.
+\section{PRESTO - PREcursor of Station TwO}
+%\textbf{PRESTO - PREcursor of Station TwO:$\;\;$}
+There are numerous activities related to the mechanical integration of the MVD currently addressed by the MVD group including a design of ultra-low material budget flex cable employing commercially available processes based on copper traces \cite{FPC}. Those cables will be used within the PRESTO module which is currently constructed. PRESTO addresses the double-sided integration of $15$ MIMOSA-$26$ sensors (dummies and working sensors) onto a $8\times 8~cm^{2}$ CVD diamond support. The reader is referred to the report \cite{PRESTO} for more details.
%The PRESTO module will employ the new flex cables \cite{FPC} providing all signals needed to operate and read out the sensors. To construct this PRESTO module, new sensor positioning jigs aiming for a sensor positioning precision w.r.t. to support and neighboring sensors of below 100~$\upmu$m were manufactured. To evaluate the integration concept, the RAL-$247$ adhesive and new jigs, a dummy PRESTO module based on $200~\upmu$m glass plate was assembled, employing $50~\upmu$m MIMOSA-$26$ dummies, see fig.~\ref{fig:picture}. The horizontal sensor-to-sensor distances were measured to be below $5~\upmu$m. The vertical shifts between sensors were measured to be of about 20~$\upmu$m. The achieved precision is significantly below the envisioned one. Next steps comprise the establishing of procedures for the integration of the flex cables, the exercise of double-sided bonding and the verification of the vacuum compatibility.
%\begin{figure}[htb]
%\centering
-%\includegraphics*[width=45mm]{integration1.eps}
-%\caption{PRESTO dummy module.}
+%\includegraphics*[width=65mm]{glue.eps}
+%\caption{RAL-$247$ adhesive modulus as a function of temperature for different irradiation types and doses.}
%\label{fig:picture}
%\end{figure}
\bibitem{glue}
Private communication, Simon Canfer Rutherford Appleton Laboratory, Composites and Materials Testing Group, UK.
+\bibitem{vacuum}
+G. Kretzschmar et al.,"Vacuum compatibility of the CBM-MVD." GSI annual report 2014.
+
\bibitem{FPC}
-P. Klaus et al., GSI annual report 2014.
+P. Klaus et al., "Ultra-low material budget Cu flex cable for the CBM-MVD. "GSI annual report 2014.
\bibitem{CVD}
Diamond Materials GmbH, Germany
+\bibitem{PRESTO}
+M. Koziel et al., "PRESTO: PREcursor of Station TwO of the CBM-MVD." GSI annual report 2014.
+
\end{thebibliography}
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