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\title{Construction and Test of New Precision Drift-Tube Chambers for Upgrades of the ATLAS Muon Spectrometer in 2016/17}

\author{\underline{H.~Kroha$^*$}\thanks{$^*$Corresponding author: kroha@mpp.mpg.de}, O.~Kortner, F.~M\"uller, S.~Nowak, K.~Schmidt-Sommerfeld
 \\ \textit{Max-Planck-Institut f\"ur Physik, Munich}}

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\begin{abstract}
	The Monitored Drift Tube (MDT) chambers of the ATLAS muon spectrometer demonstrated that they provide very precise and robust tracking over large areas.
	Goals of ATLAS muon detector upgrades are to increase the acceptance for precision muon momentum measurement and triggering and to improve the rate capability of the muon chambers in the high-background regions when the LHC luminosity increases.
	Small-diameter Muon Drift Tube (sMDT) chambers have been developed for these purposes.
	With half the drift-tube diameter of the MDT chambers and otherwise unchanged operating parameters, sMDT chambers share the advantages with the MDTs, but have an order of magnitude higher rate capability and can be installed in detector regions where MDT chambers do not fit in.
	The chamber assembly methods have been optimized for mass production, reducing cost and construction time considerably and improving the the sense wire positioning accuracy to better than ten microns.
	The construction of twelve chambers for the feet regions of the ATLAS detector is currently ongoing with the goal to install them in the winter shutdown 2016/17 of the LHC.
	Design and construction of the new sMDT chambers for ATLAS will be discussed as well as measurements of their precision and performance.
\end{abstract}


The Monitored Drift Tube (MDT) chambers of the ATLAS muon spectrometer~\cite{ATLAS} demonstrated that they provide very precise and robust tracking over large areas. Goals of ATLAS muon detector upgrades are to increase the acceptance for precision muon momentum measurement and triggering and to improve the rate capability of the muon chambers in the high-background regions when the LHC luminosity increases.
Small-diameter Muon Drift Tube (sMDT) chambers have been developed for these purposes [1]. With half the drift-tube diameter of the MDT chambers and otherwise unchanged operating parameters, sMDT chambers share the advantages with the MDTs, but have an order of magnitude higher rate capability [1] and can be installed in detector regions where MDT chambers do not fit in.
The construction of twelve chambers for the feet regions (see \fig{}) of the ATLAS detector is currently ongoing with the goal to install them in the winter shutdown 2016/17 of the LHC. The purpose is to increase the acceptance for three-point measurement in these regions which will substantially improve the momentum resolution.





We report here about the construction of these chambers which started in the fall of 2014. The chamber design
and construction procedures have been optimized for mass production while providing high mechanical accuracy
of better than 10 m in the sense wire positioning. The sMDT drift tubes are standard industrial aluminum tubes
with a diameter of 15 mm and a wall thickness of 0.4 mm.

First the drift tubes are assembled with a semi-automatized wiring machine (see Fig, 3, top). The wire tension,
the gas leak rate and the leakage current under high voltage are measured for every tube before it is assembled
in a chamber. The failure rate is only about 1%. About 100 tubes can be produced and tested per day with this
setup. The chambers are assembled by inserting the tubes with the reference surfaces on the endplugs into the
jigs at each chamber end which define the wire grid as described in Fig.2) and glueing them together and to a
spacer and support frame (see Fig. 1 and Fig. 3, bottom). A complete chamber can be assembled within one
working day. Before mounting the modular gas distribution system and the readout and high-voltage distribution
boards [1], the wire grid and the geometry of the assembled chamber is reconstructed with a few micron
precision by measuring the reference surfaces of the endplugs at both chamber ends on a coordinate measuring
machine (see Fig. 4, right). An overall sense wire positioning accuracy in a chamber of better than 10 m (see
Fig. 4, left). The positions of the optical alignment sensors on the chambers are also measured in this way with
respect to the wire grid.

Finally we report about the test results of the completed chambers in a cosmic ray teststand.



\begin{thebibliography}{99}
	\bibitem{ATLAS} ATLAS Collaboration, G. Aad et al., The ATLAS Experiment at the CERN Large Hadron Collider, \emph{JINST 3} (2008) S08003.
	\bibitem{sMDT} H. Kroha et al., Construction and test of a full-scale prototype drift-tube chamber for the upgrade of the ATLAS muon spectrometer at high LHC luminosities, Nucl. Instr. and Meth. A718 (2013) 427.
	\bibitem{Pisa} S. Nowak et al., \emph{Precision Muon Tracking Detectors and Read-Out Electronics for Operation at Very High Background Rates at Future Colliders}, Proceedings of 13th Pisa Meeting on Advanced Detectors, 2015, to be published.
\end{thebibliography}



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