\documentclass{JACoW-GSI-2014}
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- %% GSI Scientific Report 2013
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-
- \begin{document}
- \title{Towards the vacuum compatibility of the CBM micro vertex detector\thanks{Work supported by BMBF (05P12RFFC7), EU-FP7 HardronPhysics3, HIC for FAIR and GSI}}
+\usepackage{graphicx}
+% forbitten: \usepackage{url}
+\usepackage[utf8]{inputenc}
+\usepackage{amsmath}
+\usepackage{amssymb}
+%% GSI Scientific Report 2013
+%% \setlength{\titleblockheight}{27mm} KG
+\setlength{\titleblockheight}{35mm}
+
+\begin{document}
+ \title{Assessing the vacuum compatibility of the CBM micro vertex detector\thanks{Work supported by BMBF (05P12RFFC7), HIC for FAIR and GSI}}
\author[]{G. Kretzschmar}
\author[]{M. Koziel}
\maketitle
- The CBM Micro Dertex Detector (MVD) has been forseen to operate in high vacuum of about $10^{-4}$ $mbar.$ Vacuum compatibility of the MVD setup m get tested with respect to thermal management of the MVD-stations and their mechanical stability. In the following the motivation and progress to vacuum management get explained
- \vspace{-2.mm}
- \section{Motivation}
- The MVD operates in vacuum and has to be vacuum tight to $10^{-4}$ $mbar.$ In the critical points the thermal management of the MVD station has to require the material budget, radiation hardness and vacuum compatibility. The cooling support has to be vacuum tight and stands outside the critical point, but stabilize the inner parts thermally and mechanically.
-
- Also the outgasing rates of the MVD has to be compatible with the pressure of $10^{-4}$ $mbar.$
- The first steps need to evaluate the vacuum tightness of the cooling support. Leaking pipes can destroy vacuum pumps or the sensors and cooling liquid can deposit on the sensor surface. Due to low pressure the behaviour of tighness can be different to normal pressure.
- Next steps will be test of the thermal behaviour of the heatsinks of station 0 and 2 in the test setup. After these the thermal management of station 0 and station 2 with TPG and heaters get studied.
- \vspace{-2.mm}
- \section{Approach}
- Test over the last year show under vacuum condition the tighness of swagelok connectors and heatsink with siliconoil as cooling liquid is not given. The prototype heatsink used for CERN test was mounted inside the chamber and run for a week at $T=20$ $^o$C at atmospherical pressure and tightness of siliconoil got tested and critical point defined. After tightness at atmosphere was given the system got pumped by rotary pump to $10^{-2}$ $mbar$ and tested at the critical points of thightness. It shows up to make a difference and it was not possible with these setup and Swaegelok connection to work with siliconoil under vacuum condition. The cooling liquid got shifted to glycol mixed with destillated water 1:1 and vacuum tightness got evaluated. Test to vacuum tightness of cooling by siliconoil got shifted after thermal test.
-
- The heatsink of Station 0 cooled by glycol got mounted inside the vacuum chamber and tested under atmosphere of tightness and after these at vacuum. The endpressure is now at $1 \circ 10^{-4}$ $mbar$ with Turbomolecularpump and prepump. These pressures came from outgasing of heatsinks and leaks of the vacuum vessel. The thermal readout is done by a combination of PT100 contact sensors and infrared Thermographie through an infrared vacuum window and black painted heatsink. The infrared Thermographie shows optical interferences of vacuum window and the camera and cannot easilly removed. So only difference measurements are possible by these setup and the real Temperature has to be read out by contact sensors. The right glueing of Temperature sensors make till now problems and the thermal read out is not ready till now.
- Test for clamping with cooper as support material and kapton heaters as MIMOSIS under vacuum show the heat paste is vacuum compatible.
-
-
- \vspace{-2.mm}
- \section{Status}
- The Heatsink station 0 is mounted and connected. Thermal read out is problematic and still under evaluation. Here the glueing of PT100 sensor at lower Temperatures is still problematic.
- Compatibility with thermal management of heatpaste must get evaluated.
- Vacuum tight cooling support of siliconoil is not given.
- Thermal test in difference mode can directly made and real Temperature test after the thermal read out is ready.
- \begin{thebibliography}{1} % Use for 1-9 references
- \bibitem{}
- \end{thebibliography}
- \end{document}
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+The CBM micro vertex detector (MVD) will operate in a moderate vacuum of about $10^{-4}$ $mbar$ to minimize multiple scattering. The vacuum compatibility of the detector needs to be validated with respect to thermal management of the MVD-stations and their mechanical integrity during the design and prototyping phase. A dedicated vacuum vessel, located at the IKF Frankfurt, allows for systematic studies w.r.t. selection of material, detector operation and cooling in vacuum.
+
+The setup comprises a 260 liter stainless steel vacuum chamber with multiple flanges providing a flexible access to the interior part and the fitting of all MVD stations inside, see fig. \ref{fig:vacuum} right picture. The chamber is supplied with a combination of a rotary and a turbomolecular pump allowing to routinely reach the pressure of $2 \cdot 10^{-6}$ $mbar$, despite of the chamber volume and the variety of feedthroughs for signals and cooling media. The pressure is measured with two penning-pirani sensor systems. Special emphasis is put on safely operating the detector at temperatures below room temperature and hence, active cooling inside the vessel is mandatory.
+
+To test possible media for cooling and to select a reliable concept of piping inside the vacuum, a copper pipe of 6 mm outer diameter and 3 mm inner diameter was subdivided into smaller pieces and interconnected with Swagelok fittings to form in total about 1 m long cooling circuit. The circuit was next placed into the vacuum chamber and connected to the outside-chamber cooling system (HUBER). The standard Si-oil cooling liquid was then circulated at atmospheric pressure where no leak was observed and at pressure of $10^{-2}$ $mbar$, where signs of the coolant were spotted on the Swagelok connectors placed inside the vacuum. After excluding all mechanics-related reasons for observed leaks, the cooling liquid was changed to glycol. After this change no leaks were observed, also when replacing the copper pipes with polyurethane pipes. These studies underline the need of a careful preparation of reliable pipe interconnections and do suggest not to employ
+coolants which feature strong creeping, like silicon oil.
+
+Outgassing of materials has to be kept at a minimum, both to not spoil the vacuum close to the target and to avoid the contamination of surface. The setup allows to characterize outgasing of detector components, like (flex) cables, adhesives or readout boards. Outgassing rates of MVD components will be measured with the so-called throughput method or the gas accumulation method mentioned in \cite{Redhead} and the ratio of probe to vessel surface should be higher. This especially means to switch to a smaller vacuum vessel.
+
+The vacuum setup allows for evaluation of thermal management of the MVD components, i.e. heat-sinks and sensor carriers based on high-performance materials like chemical vapor deposition (CVD) diamond and thermal pyrolitic graphite\footnote{Materials selected due to their outstanding heat conductivity, allowing at the same time a minimum material budget, which represent another important constrain for the MVD.} (TPG). The evaluation is carried out by contact temperature sensors (DS1820) in combination with a high-resolution infrared camera positioned outside of the chamber (through a zincselenide window transparent for infrared). The contact sensors serve as a reference for the infrared-based characterization of the detector setup, and they allow at the same time for a proper calibration of IR camera with respect to the reflectivity of materials and reference measurements. To emulate the expected MVD-sensor heat dissipation, Kapton flexible heaters from OMEGA \cite{OMEGA} are glued on materials under evaluation, see figure \ref{fig:vacuum}.
+
+It is planned to characterize in vacuum full-size detector prototypes like PRESTO (PREcursor of the Second sTatiOn), see \cite{PRESTO}, with a focus on the longterm operation in vacuum.
+
+
+
+ \begin{figure}[htb]
+ \centering
+ \includegraphics*[width=85mm]{report.eps}
+ \caption{Left: IR picture at $10^{-4}$ $mbar$ and heater at 1.12~W/cm$^2$ on copper carrier. Right: full-size half-station heat-sink of the MVD station 0 located in the vacuum chamber.}
+ \label{fig:vacuum}
+ \end{figure}
+
+
+
+
+
+
+
+ \begin{thebibliography}{9}
+
+ \bibitem{PRESTO}
+ M. Koziel et al., "PRESTO: PREcursor of the Second sTatiOn of the CBM-MVD." GSI annual report 2014.
+
+\bibitem{Redhead}
+P. A. Redhead, ``Recommended practices for measuring and reporting outgassing data'',
+National Research Council, p.~4, Ottawa ON K1A 0R6, Canada
+
+\bibitem{OMEGA}
+OMEGA Engineering, INC. (www.omega.com)
+
+%\bibitem{glycol}
+%Aqua-Concept Gmbh, Germany (www.aqua-concept-gmbh.eu)
+\end{thebibliography}
+ \end{document}
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