%% \setcounter{figure}{0}
%
% This is file: s-smalltube.tex
% -----------------------------
%
\newpage

\section{Small-Diameter Muon Drift Tube Detectors}

\if{0}
{\it Detail of detector technologies proposed for use in the small wheel 
detector, including the status of developments. Include a description
on the status and size of available prototype chambers.\\

This section should describe the technology up to the level of a
single chamber.
}
\fi

%%% ==== B1 ============================================================
%%%
\subsection{Tracking in a high--back\-ground environment}
\label{Tracking}
%%%
%%% ====================================================================

In order to study the performance of the MDT chambers at high background rates, a full-scale ATLAS
BOS chamber has been extensively tested in the CERN Gamma Irradiation Facility
(GIF)~\cite{ref_deile,ref_horvat}. The results showed that the drift-tube chambers provide
efficient and high-resolution tracking in combination with fast trigger and second-coordinate
chambers up to very high occupancies above 20~\%~\cite{ref_MDTtracking} which will be reached 
in the ATLAS endcap muon spectrometer already at twice the LHC design luminosity. 

Reduction of the outer drift-tube diameter from 30~mm in the present ATLAS Monitored Drift Tube
(MDT) chambers to 15~mm while keeping the other parameters, including the gas gain of $2\cdot
10^4$, the sense wire diameter of $50~\mu$m and  the tube wall thickness of 0.4~mm unchanged leads
to a significant improvement of the rate capability  of the drift-tube chambers which is more than
sufficient for their operation in the new Small Wheels at the highest background rates
expected for LHC luminosity upgrades in the forward regions of the ATLAS muon spectrometer.  

T%
% --- Fig. 25 ----------------------------------------------------------------
%

\begin{figure}[!htb]

\centering
\includegraphics[width=0.48\textwidth]{Figures/dtspectrum}
%%\hspace{2mm}
\includegraphics[width=0.48\textwidth]{Figures/rtrelation}
%\vspace{-1cm}

\caption{Drift time spectrum (left) and space-to-drifttime (r-t) relationship (right) of circular
drift tubes  of 30~mm and 15~mm diameter operated with Ar:CO$_2$ (93:7) gas mixture at 3 bar and
gas gain of 20000. The Garfield simulation~\cite{ref_garfield} of the drift time spectrum of 15~mm
tubes is overlaid.} 

\label{fig_dtspectrum}
\end{figure}

The standard MDT operating parameters are kept for the small-diameter drift tubes (see
Table.~\ref{Sml_MDT_parameters}). With the MDT gas mixture of Ar:CO$_2$ (93:7) at 3 bar absolute
pressure, the gas gain of $2\cdot 10^4$ is achieved at an operating voltage of 2730~V for 15~mm
diameter drift tubes.  Under these conditions, the maximum drift time is reduced by a factor of 3.8
from about 700~ns to 185~ns by shrinking the tube diameter by a factor of two (see
Fig.~\ref{fig_dtspectrum}, left)~\cite{ref_bittner1}. In addition, the background flux hitting a
tube is reduced by a factor of two.  Altogether, the drift-tube occupancy is reduced by a factor of
7.6.   2 x 6 drift-tube layers at radii $R<220$~cm in the Small Wheels and 2 x 4 layers at larger
radii are sufficient  to provide very robust tracking with track segment reconstruction
efficiencies of better than 99~\% up to the highest expected background rates (see details of the
chamber performance below). 

%
% --- Table  9 -------------------------------------------------------------------
%

\begin{table}[!htb]

  \begin{center}
%   
    \begin{tabular}{|l|c|} \hline

     \textbf{Parameter}        &      \textbf{Design value}   \\  \hline

    Tube material              &      Aluminum                \\ 
    Outer tube diameter        &      15.000\,mm              \\
    Tube wall thickness        &      0.4\,mm                 \\ 
    Glue gap between tubes     &      0.1\,mm                 \\
    Wire material              &      Gold-plated W/Re (97/3) \\
    Wire diameter              &      50~$\mu$m               \\
    Wire tension               &      $300\pm 15$~g           \\
    Gas mixture                &      Ar/CO$_2$/H$_2$O (93/7/$\leq 1000$~ppm) \\
    Gas pressure               &      3 bar (absolute)        \\
    Gas gain                   &      2 x $10^4$              \\
    Wire potential~~~~~~~~~~~~~&      2730 V                  \\
    Maximum drift time         &      $\sim$ 185 ns           \\
    \hline

    \end{tabular}
   \caption{The operating parameters of small-diameter MDT chambers.\label{Sml_MDT_parameters}}
  \end{center}
%
\end{table}


The space-charge distribution caused by the ion clouds drifting towards the tube wall during a
particle crossing modifies the local electric field, influencing both the drift velocity and the
gas gain. By lowering the effective potential experienced  by the electrons drifting towards the
wire, high background flux leads to decreasing gas gain. The resulting signal loss grows with the
inner tube radius $r_2$ proportional to $r_2^3\cdot \ln (r_2/r_1)$ ~\cite{ref_riegler},  where
$r_1=25~\mu$m is the wire radius, and therefore is 8.7 times smaller in 15 mm compared to 30 mm
diameter drift tubes. 
Fluctuations of the space charge and, therefore, of the electric field lead to variations of the
drift velocity causing a deterioration of the spatial resolution in non-linear drift gases like
Ar:CO$_2$ (93:7) where the drift velocity depends on the electric field. This effect increases
strongly with the drift distance above a value of 7.5~mm while the gain drop effect on the
spatial resolution dominates for distances close to the sense wire  (see
Fig.~\ref{fig_dtresolrate30mm}, left) ~\cite{ref_aleksa,ref_deile,ref_horvat}).
For 15~mm diameter tubes with drift radii below 7.1~mm, the effect
of space charge fluctuations is essentially eliminated leading to a reduction 
in the degradation rate of the average spatial resolution by another factor of 2.

For drift radii below 7.5~mm, i.e. for the 15~mm diameter tubes, the space-to-drift time
relationship is close to linear leading to a reduced sensitivity to environmental parameters such as
gas composition and density, magnetic field and irradiation rate variation (Fig.~\ref{fig_dtspectrum},
right).
%
% --- Fig. 26 ----------------------------------------------------------------
%

\begin{figure}[!htb]
\centering
\includegraphics[width=0.60\textwidth]{Figures/dtresolrate30mm_CC}

\caption{Spatial resolution of 30~mm diameter drift tubes (with time-slewing corrections) 
as a function of the drift radius for
different background hit rates as measured at the GIF~\cite{ref_deile,ref_horvat}.} 

\label{fig_dtresolrate30mm}
\end{figure}

%
% --- Fig. 27 ----------------------------------------------------------------
%

\begin{figure}[!htb]
\centering
\includegraphics[width=0.50\textwidth]{Figures/dtresolrate_CC}

\caption{Dependence of the {\it average} drift tube resolution (with time-slewing corrections) 
on the background hit rate.
The measurements for 30~mm and 15~mm diameter drift tubes at the GIF are compared.}

\label{fig_dtresolrate}
\end{figure}


%
% --- Fig. 28 ----------------------------------------------------------------
%

\begin{figure}[!htb]
\centering
\includegraphics[width=0.44\textwidth]{Figures/nsw_resol_CC}
\includegraphics[width=0.44\textwidth]{Figures/nsw_angresol_CC}

\caption{Radial dependence of the 
{\it average} point (left) and angular (right) resolution of the sMDT chambers in the NSW  
for the maximum background flux corresponding to 14 kHz/cm$^2$ at the inner bore and without background irradiation for the
baseline layout and an alternative layout with two additional tube layers per multilayer at $R<160$~cm.
The spatial resolution is quoted for the average number of hits in the chambers depending on the background counting rate
taking into account the measured drift tube efficiency.  
The angular resolution is shown for the maximum time resolution of the TDC used in the offline reconstruction
and for 12.5 ns coarser time digitization for the use of the MDT chambers in the L1 muon trigger 
%The combined spatial and angular resolutions of the trigger chamber-sMDT system are also shown as a function of R.
.}

\label{fig_nswresol}
\end{figure}

Since the spatial resolution of the drift tubes improves with increasing drift radius, the average
single-tube resolution at low background rates is
degraded from $83~\mu$m for 30~mm diameter tubes to $110~\mu$m for 15~mm diameter tubes after applying 
time-slewing corrections. 
Fig.~\ref{fig_dtresolrate} shows the dependence of the average 30~mm and 15~mm diameter
drift tube resolution on the background hit rate measured at the GIF. The measurements for 15~mm diameter tubes
agree well with the expectation from the 30~mm diameter tube measurements  
derived by averaging over the drift radius range $r<7.5$~mm in Fig.~\ref{fig_dtresolrate30mm} 
and scaling the corresponding background rates with the factor 8.7 to account for the reduced gain loss. 
The measurements confirm the expectation that
the degradation rate of the spatial resolution with the background flux is reduced by a factor of 10 for 15~mm
compared to 30~mm diameter tubes.

The average 15~mm diameter drift tube resolution is $143\pm 4~\mu$m at the maximum background hit rate of 10~kHz/cm$^2$
at which GIF measurements could be performed. At 14 kHz/cm$^2$ rate it will still be better than $170~\mu$m.
Consequently, the track point resolution of the sMDT chambers in the proposed NSW layout 
with 2 x 4 (2 x 6) tube layers for $R> 200$~cm ($R<200$~cm)
is better than $46~\mu$m for $R>160$~cm and better than $60~\mu$m for smaller radii R in the NSW 
at the highest background rates corresponding to 14 kHz/cm$^2$ at the inner bore (see Fig.~\ref{fig_nswresol}). 
The sMDT chamber resolution quoted corresponds to the average number of hits in the chambers as a function of the background
counting rate taking into account the measured $3\sigma$ efficiency of the drift tubes (see Fig.~\ref{fig_efficiency_GIF11}). 
Fig.~\ref{fig_nswresol} also shows
the sMDT chamber resolution for an optional alternative layout with two additional tube layers per multilayer at $R<160$~mm. 
%as well as the spatial resolution of the combined trigger chamber-sMDT system as a function of R at the highest rates. 
%The combined resolution is better than xxx over the whole radial range.
With the additional tube layers, the sMDT chamber resolution at $R<160~\mu$m is improved 
to better than $50~\mu$m. Without background irradiation, the sMDT chamber resolution is better than $40~\mu$m over the whole NSW.
The combination of the tracking information of the sMDT and trigger chambers will give considerable further improvement of the 
resolution.
%The spatial resolution of the MDT chambers in the present Small Wheels at the LHC design luminosity (corresponding   
%to 500 Hz/cm$^2$ background flux at the border to the CSC region) is also shown in Fig.~\ref{fig_nswresol} for
%comparison.  

The angular resolution is only relevant for the use of the MDT chambers in the future L1 muon trigger in combination with the
trigger chambers.
It is limited by the lever arm available for the drift tube chambers in the Small Wheels. 
On the trigger level, 1 mrad angular resolution is achieved in the radial range $R>125$~mm corresponding
to $\|\eta \| < 2.4$ covered by the L1 muon trigger. 
% ==== B2 ============================================================
%%%
\subsection{Chamber Design}
\label{Technical_Implementation}
%%%
%%% ====================================================================

The design of the muon drift-tube chambers with 15~mm diameter tubes for the new Small Wheels
follows as closely as possible  the current ATLAS MDT chamber design in the endcap region of the muon
spectrometer (Fig.~\ref{fig_smdt_chamber_design}).  The chambers consist of two multilayers of
four or six layers of drift tubes each in densest package. The aluminum tubes of 15~mm outer
diameter and 0.4~mm wall thickness are produced according to industry standard and are chromatized
for cleaning and reliable electric contact. The tubes are separated by 0.1 mm wide glue gaps during
chamber assembly. The two multilayers are separated by a spacer frame carrying the supports of the
integrated drift-tube and trigger chambers on the Small Wheel structure and the in-plane optical
alignment system monitoring the planarity of the chambers. The aluminum spacer frame is of 
similar design as for the present Small Wheel MDT chambers. Modification in the chamber
design are mainly due to the four times denser packaging of the drift tubes and their gas and electrical 
connections.

Central to the chamber design is the design of the drift tubes and of their endplugs (see
Fig.~\ref{fig_smdt_tube_design}).  The aluminum tubes of 15~mm outer diameter and 0.4~mm wall
thickness are produced according to industry standards (DIN) with tolerances of $\pm 0.1$~mm on
diameter, roundness and concentricity of inner and outer circumference and of $\pm 0.5$~mm on
straightness and chromatized for cleaning and reliable electric contact. The endplugs insulate the
sense wire from the tube wall, center the wire in the tubes, position it with respect to the 
external reference surface on the endplug  with an accuracy of better than $10~\mu$m and provide
high-voltage-safe connections to the gas distribution manifold  (see
Fig.~\ref{fig_gasmanifold_design}) and to the  24-channel readout and high-voltage interface boards 
(''hedgehog cards'', Figs.~\ref{fig_hedgehogs}). 

%
% --- Fig. 29 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.8\linewidth,clip]{Figures/gasmanifold_design}

\caption{Design of the gas manifolds. The gas inlet and outlet bars are 
located at opposite ends of the tube multilayers.}
\label{fig_gasmanifold_design}
% 
\end{center}
\end{figure}


The wire is fixed at both tube ends in copper crimping tubes inserted into the central brass
inserts of the endplugs and connected to the signal and high-voltage hedgehog cards via brass signal
caps which are screwed onto the brass inserts, sealing the tubes with respect to the gas manifold
with O-rings. The brass insert of the endplug holds the spiral-shaped wire locator (''twister'') in
a central bore on the inside of the tube and  transfers the wire position to the precisely machined
reference surface at the outside of the tube  which is used to accurately position the drift tubes
during chamber assembly. The wire position information is transferred solely via the precision
machined brass insert; precision machining of the complete endplugs is not necessary anymore,
facilitating the production of the tubes and improving the accuracy of chamber construction. The
two most critical problems for the ATLAS MDT drift tube production, cracking of the
Noryl\textsuperscript{\textregistered} plastic insulator and precision machining of the injection
moulded endplugs, have been eliminated by the new design.      

The insulators of the endplugs consist of Crastin\textsuperscript{\textregistered}, a PBT based
thermoplastic with 30~\% glass fiber admixture to improve mechanical stability  which shows little
shrinkage and outgassing and, unlike Noryl\textsuperscript{\textregistered} (material in the
present MDT endplugs), high stability against cracking under stress. The material is of similar
chemical composition as Pocan\textsuperscript{\textregistered}  which is used for the injection
moulded components of the gas manifolds of the present and the new drift tube chambers.  The
endplugs are fabricated by injection moulding and sealed in the aluminum tubes with O-rings by
circular mechanical crimping  of the tube walls.   

The modular gas distribution system consists of injection moulded plastic tubes made of
Pocan\textsuperscript{\textregistered} without glass fiber which interconnect adjacent tubes in
the direction perpedicular to the multilayer and connect them to an aluminum gas distribution bar
on the readout and the high-voltage end of the multilayer (see Figs.~\ref{fig_gasmanifold_design}
and \ref{fig_gasmanifold_photo}). 

%
% --- Fig. 30 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.5\linewidth,clip]{Figures/gasmanifold_photo}
%
\caption{Picture of the gas manifold mounted on the prototype chamber.}
\label{fig_gasmanifold_photo}
% 
\end{center}
\end{figure}

The readout and high-voltage supply scheme follows closely the one of the present MDT chambers
using the same parameters and specifications. The high-voltage decoupling capacitors on the readout
side and the terminating resistors on the high-voltage supply end are individually encapsulated in
plastic containers for high-voltage protection. The plastic containers are integrated with the
hedgehog cards plugged onto the gold-plated pins of the signal caps and ground connectors. The
ground pins are screwed into the gaps formed by three adjacent tubes (see
Figs.~\ref{fig_smdt_tube_design} and \ref{fig_gasmanifold_photo}) during chamber assembly to
connect the tube walls to the ground of the hedgehog cards. This scheme allows for the
high-voltage-free design of the readout hedgehog cards. 

Each passive readout hedgehog card is connected to an active front end electronics board (mezzanine card) for 24 channels 
carrying new radiation hard ASICs, three 8-channel amplifier-shaper-discrimiator (ASD) chips and one 32-channel HPTDC chip 
(see below). The mezzanine cards follow one-to one the shape of the hedgehog cards and are already under development. The
electronics boards are enclosed in chromatized aluminum Faraday cages which also shield the readout hedgehog
cards from the mezzanine cards.  


%%% ==== B2.2 ============================================================
%%%

\subsection{Readout Electronics}
\label{readout_electronics}


The readout of the Small MDT tubes will follow the proven architecture of the present MDT
system. A number of additions and modifications, however, will be necessary in order to
adapt the rate capability of the readout chain to the requirements of the SLHC. For the
mechanical integration of the readout electronics with the Small tube chambers, the
layout of the electronics will have to be adapted to the 4 times higher tube density at
the ends of the Small tube chambers. Finally, the radiation tolerance of all components
will have to comply with the high radiation levels, in particular at the inner border of
the Small Wheel.


%% ----- 5.5.1-----------------------------------------------------------
%%
\subsubsection{Architecture of the present MDT readout}
\label{MDT_architecture_appendix}
%%
%% ----------------------------------------------------------------------

In the present readout scheme tube signals are routed via a PCB ("hedgehog card") to a
piggy-back card ("mezzanine card"), containing an Amplifier and Shaper, followed by a
Discriminator with adjustable threshold, all three functions being integrated in a
radiation tolerant ASIC (ASD). The discriminator outputs, in turn, are routed to a TDC,
where each leading and trailing edge signal receives a high-precision time stamp, which
is retained, together with the corresponding channel number, in a large internal buffer
of the TDC ("Level-1 buffer").

When the TDC receives a Level-1 trigger, a subset of the recorded hits, corresponding to
a pre-defined time window, are retained for readout and are forwarded to the data
concentrator of this chamber, the "Chamber Service Module" (CSM). From there, data are
sent to the off-chamber electronics in USA15, the "Readout Driver" (ROD). A CSM can
serve up to 18 mezzanine cards. The operation parameters of the analog frontend (ASD)
and the TDC are controlled by a JTAG string, which is distributed by the Detector
Control System (DCS) to the CSM, which sends it individually to each mezzanine card.
Fig.~\ref{readout_chain} gives the layout of the present system. A detailed presentation
of the MDT readout electronics is given in ~\cite{MDT_ELX_paper}. The ASD and TDC ASICs
are described in ~\cite{ASD_manual} and ~\cite{TDC_manual}.

\if{0}

%% Fig. NN ---------------------------------------------------------------------------

\begin{figure}[!htb]
%
\begin{center}
%
\includegraphics[width=0.45\linewidth,clip]{Figures/MDT_electronics_scheme_old_BB}
%%\hspace{2mm}
\includegraphics[width=0.39\linewidth,clip]{Figures/NSW_ELX_diagram_w_GBT}

\caption{Schematic diagram of the present (left) and of the future MDT readout chain (right). The
Chamber Service Module (CSM) collects all data of a given chamber and sends them to the ROD via an
optical link. Up to 18 TDCs can be serviced by a CSM. The 40 MHz clock and the Level-1 trigger are
broadcast by the TTC system to the TDCs.}

\label{readout_chain}

\end{center}

\end{figure}

\fi


%% ----- 5.5.2-----------------------------------------------------------
%%
\subsubsection{Architecture of the readout for sMDT chambers}
\label{MDT_architecture_Small_tubes_appendix}
%%

For the evolution of this architecture into matching the requirements of the Small tube
readout, a number of problems limiting the performance of the present scheme has to be
overcome. Given the high rate capability of the Small MDT tubes, the bandwidth of the
readout system has to be increased. Due to the limitations of the internal buffering
scheme and processing speed, the present TDC can only handle average tube rates up to
about 300 kHz per tube without losing data, while Small tubes would operate beyond 1 MHz
per tube. Therefore, an improved TDC is an essential requirement for a new readout
design. Another limitation of the readout bandwidth comes from the optical link,
connecting the CSM to the ROD, as the S-link protocol only supports a usable bandwidth
of 1,4 Gbit/s. Fig.~\ref{occ_and_link} shows occupancy and efficiency of Large and Small
tubes as a function of tube hit rate.


\if{0}

%% Fig. NN ---------------------------------------------------------------------------
%
\begin{figure}[!htb]
%
\begin{center}
%
\includegraphics[width=0.50\linewidth,clip]{Figures/Elx_diagram_sm_tubes}

\caption{Schematic diagram of the chain for the readout of the Small tube chambers. The
higher tube density at the tube ends requires a higher modularity for the readout architecture.}

\label{Elx_diagram_sm_tubes}

\end{center}

\end{figure}

\fi

%% ---------------------------------------------------------------------------------

When upgrading the performance of ASICs (ASD, TDC), we have to take into account that
their technologies are no longer supported by industry. The following new components had
therefore to be introduced into the readout system.


%% duplicate figure

\if{0}


%% Fig. NN -------------------------------------------------------------------------

\begin{figure}[!htb] 

\begin{center}

\includegraphics[width=0.5\linewidth,clip]{Figures/NSW_efficiency_occupancy_saturation_CC}

\caption
{Green: Occupancy as a function of tube hit rate, assuming a dead time of 200 ns
(equal to the maximum drift time) after each hit.
Red: Resulting efficiency with the same dead time. Blue: Saturation of the mezzanine-to-CSM link,
showing the base load of 15\% due to the overhead of the transfer protocol at zero rate.
}

\label{occ_and_link}
\end{center}
\end{figure}

\fi

\begin{enumerate}

  \item[(a)] The ASD is re-designed in the IBM 130 nm technology. A 4-channel
  prototype, demonstrating the analog parameters, has already been produced and tested and works
  correctly. Most analog parameters of the previous design are preserved. 
  The 4-channel version of the complete ASD chip has been delivered and bonded 
  and is ready for testing.  

  \item[(b)] The TDC will be replaced by the HPTDC, designed by the CERN-MIC group
  (~\cite{The_HPTDC}). This 32-channel device has an improved internal buffering
  scheme as well as higher transfer and processing speeds.

  \item[(c)] The CSM collects data from a MDT chamber formats the event and sends
  data, trigger-by-trigger, via an optical link to the ROD in USA15. All logical
  operations are performed by an FPGA, which will need to be upgraded to higher
  radiation tolerance. The interface to DCS, needed for controlling electrical and
  temperature parameters on the chamber will be done via the GBT (see below). The
  adapter box to the CANbus (ELMB) can therefore be dropped, reducing complexity of
  cabling.

  \item[(d)] The link connecting the CSM to the ROD will be replaced by a GigaBit
  Transmitter link (GBT), developed by CERN. This link provides a 3 times higher
  transfer rate (Gbit/s), compared to the S-link~\cite{GBT}.  

\end{enumerate}

% -------------------------------------------------------------------------------

Another stringent requirement for the realization of the new readout scheme is
the mechanical integration of the on-chamber readout electronics with the chamber
mechanics, as the density of channels at the tube ends is four times higher than in the
case of the Large tubes. The following design changes will therefore be implemented.

\begin{enumerate}

  \item[(a)]
  HV decoupling capacitors are located in 15 mm diame`ter cylinders at the tube ends, see
  Fig.~\ref{fig_hedgehogs}. The density of signal routing on hedgehog cards
  is thus no longer limited by HV insulation distances between HV 
  and signal traces on the PCB. 

  \item[(b)] To match the higher tube density, the space on the mezzanine card has to be used
  more efficiently. For this purpose, the passive protection circuitry of the ASD inputs
  will be moved to the hedgehog card. In addition, the modularity of the ADSs will be
  changed from 8 to 16 channels per chip, which goes well with the 32-channel modularity
  of the HPTDC.  

  \item[(c)] For the interconnection between mezzanine cards and New CSM 
  we foresee to use the same 40-wire cables as was used in the present system. 
  Its moderate diameter and high flexibility may be important for fitting the new MDTs
  into the limited space in the Small Wheel.
  
\end{enumerate}


%%% ==== B3 ============================================================
%%%
\subsection{Chamber Construction}
\label{chamber_assembly}
%%%
%%% ====================================================================

\if{0}

{\it
  Describe the assembly procedure. Include details on
  \begin{enumerate}
  \item Achieved mechanical precision of signal generating parts
    (i.e. strips or wires)
  \item Speed of assembly
  \item Splitting of work and logistics between production site
  \end{enumerate}
}

\fi

%% ------- B3.1 -------------------------------------------------------------
%%
\subsubsection{Drift tube production}
\label{Production of the drift tubes}
%%
%% --------------------------------------------------------------------------

The drift tubes are fabricated and tested in a climatized clean room of class 10000 using a
semi-automated assembly station  (Fig.~\ref{fig_wiringline}). The wires are fed through the
tube by air flow without touching them by hand. Wire tensioning and
crimping is performed fully automatically. After fabrication, the tubes are immediately tested for
wire tension, gas tightness and leakage currents under high voltage (see below). 
A production speed of 120 drift tubes per day has already been achieved.

%
% --- Fig. 31 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.45\linewidth,clip]{Figures/fig_wiringline}
%
\caption{Semi-automated drift tube assembly station.}
\label{fig_wiringline}
% 
\end{center}
\end{figure}


%% ------- B3.2 -------------------------------------------------------------
%%
\subsubsection{Chamber assembly}
\label{Precision_placement_of_tubes}
%%
%% --------------------------------------------------------------------------

The individual tubes are assembled to chambers using precision jigs on a flat granite table in a
climatized clean room as shown in Figs.~\ref{fig_jigging}. The jigs are
machined with an accuracy of better than $10~\mu$m. The two multilayers are assembled and glued 
together within one working day using two identical jigs. The assembly procedure is illustrated in
Fig.~\ref{fig_prototype_assembly}. The jig elements which position the endplugs
and sense wires of each layer in the transverse plane are stacked layer-by-layer forming a precise
two-dimensional grid.  Bearings for mounting of the trigger chambers and, for the first multilayer,
platforms holding the external alignment sensors  are glued to the bottom tube layers positioning
them precisely with respect to the assembly jigs and, consequently, to the wires. 

%
% --- Fig. 32 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.85\linewidth,clip]{Figures/jigging_BB}
%
\caption{Assembly tooling for the sMDT chambers with precise positioning of the endplugs
of the drift tubes holding the sense wires. The jigs are modular and adjustable for the 
construction of different chamber types. References for the precise mounting of the alignment 
sensor platforms with respect to the wires are part of the jig design.}
\label{fig_jigging}
% 
\end{center}
\end{figure}

On the second day, after letting the glue cure over night, the spacer frame is glued to the top of
the first multilayer in its jig and the in-plane alignment system is calibrated. The second
multilayer is removed from the jig and glued to the top of the spacer, aligning it precisely with
respect to the assembly jig and thus to the first multilayer. Monitoring of the tube and layer
positions during chamber construction is not necessary with this assembly scheme which has been demonstrated
by the protyotype chamber construction (see below).    

After the assembly of the drift tubes, the mounting of the gas manifolds and testing for leak
tightness requires about one week. Another two weeks are foreseen for mounting of the hedgehog
cards, installation of the Faraday cages and cabling of the chamber. Mounting of the trigger
chambers on the drift tube chambers and combined test will likely be performed at CERN.  

%% --------- B3.3 -----------------------------------------------------------
%%
\subsubsection{Prototype chamber construction}
\label{Prototype_production}
%%
%% --------------------------------------------------------------------------

A full-scale prototype of a 15~mm diameter drift tube chamber for the innermost region of the Small
Wheels presently covered by CSC chambers has been constructed in 2010 (see
Figs.~\ref{fig_prototype_assembly} and tested in the CERN Gamma Irradiation Facility GIF  as well
as in the H8 testbeam in 2010 and 2011. The chamber consists of 2 x 8 layers of drift tubes and is
readout with the existing MDT mezzanine cards and Chamber Service Module (CSM). With this prototype
chamber all aspects of the chamber design and performance as well as the construction
and test procedures have been verified and the required time and manpower for chamber production
and test has been evaluated in detail. With a semiautomated drift tube assembly station, more than 100
drift tubes have been routinely produced per day. The tubes assembled every
day will be tested for gas tightness and leakage currents under high voltage in an automated test
stand over night. 

%
% --- Fig. 33 ----------------------------------------------------------------
%

\begin{figure}[!htb]
\begin{center}
\includegraphics[width=0.48\linewidth,clip]{Figures/prototype_assembly1}
\includegraphics[width=0.48\linewidth,clip]{Figures/prototype_assembly2}
\label{fig_prototype_assembly}
%
\caption{The sMDT prototype chamber during and after assembly, 
         consisting of two multilayers with 8 tube layers each, 
         72 tubes per layer and 1152 tubes in total.}
%
\end{center}
\end{figure}

The wire positions in the two larger trapezoidal sectors of the prototype chamber equipped with
readout electronics have been measured using 600k cosmic ray muon tracks in the cosmic ray test
stand at LMU Munich. In the horizontal (y) direction, the individual coordinates have been
determined with an  accuracy of about 5 microns (see Fig.~\ref{fig_wire_ygrid_fitted}). In the
vertical (z) direction, the layer-to-layer distances have been measured with similar accuracy (see
Fig.~\ref{fig_zgrid_fitted}). Two BOS MDT chambers with known wire positions from X-ray tomograph
measurements were used as tracking references. The same setup has been used to measure the wire
positions in all ATLAS BOS and BOF MDT chambers. It will also be used to measure the positions of
the wires and of the alignment sensors of the chambers for the NSW.

The geometrical parameters of the chamber given in Table~\ref{tab_wirepos} have been determined
from a fit  to the measured wire positions. They are in excellent agreement with the design values
in y direction. In z direction, where the measurement accuracy is less, there are minor
deviations.  The distributions of the residuals of the measured wire positions in y direction and
of the measured layer-to-layer distances in z direction with respect to the ideal grid (left) and
to the measured grid (right) are shown in Figs.~\ref{fig_wire_ypos} and \ref{fig_layer_zpos},
respectively. 
All tracks crossing the chamber over the whole tube length were used for the wire position
measurement  which therefore comprises wire positioning uncertainties at both tube ends. The
uncertainty in the wire sag is below $5~\mu$m. The wire positioning accuracy at each chamber end is
thus given by the width of the residual distribution devided by $\sqrt{2}$. It is better than
$20~\mu$m in y and z direction. The residuals are nicely Gaussian distributed around zero and show
no   significant systematic deviations from the expected grid. 


\begin{table}[!htb]

  \begin{center}
%   
    \begin{tabular}{|l|c|c|} \hline 

   Parameter                 & Nominal value [mm]   & Measured value [mm] \\ \hline
   Wire pitch y              & 15.100               & $15.1018\pm 0.0003$  \\
   Wire pitch z              & 13.077               & $13.091\hphantom{8}\pm 0.007$ \\
   Relative layer shift y    & $\hphantom{1}7.550$  & $\hphantom{1}7,550\pm 0.0005$ \\ 
   Multilayer z distance     & 90.400               & $90.382\pm 0.010$ \\ \hline 
   $\sigma_y$ w.r.t.\ nominal grid & 0.020    & 0.018                  \\    
   $\sigma_y$ w.r.t.\ fitted grid  & 0.020    & 0.016                  \\    
   $\sigma_z$ w.r.t.\ nominal grid & 0.020    & 0.016                  \\    
   $\sigma_z$ w.r.t.\ fitted grid  & 0.020    & 0.013                  \\    

   \hline
   \end{tabular}
   \caption{Geometrical parameters of the sMDT prototype chamber. The values measured using cosmic ray muon tracks agree 
very well with the design values. The uncertainties in the wire coordinates in y and in the layer distances in z direction
at each chamber end with respect to the nominal and to the measured grid, respectively, are also given.}
			
	\label{tab_wirepos}
  \end{center}
%
\end{table}

%
% --- Fig. 34 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.7\linewidth,clip]{Figures/wire_ygrid_fitted}
%
\caption{Residuals of the measured wire coordinates in the horizontal (y) direction with respect to the
fitted wire grid using 600k muon tracks registered in the cosmic ray test stand.}
\label{fig_wire_ygrid_fitted}
% 
\end{center}
\end{figure}
%
% --- Fig. 35 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.7\linewidth,clip]{Figures/wire_zgrid_fitted}
%
\caption{Residuals of the measured wire coordinates in the vertical (z) direction with respect to the
fitted wire grid using 600k muon tracks registered in the cosmic ray test stand.}
\label{fig_wire_zgrid_fitted}
% 
\end{center}
\end{figure}

%
% --- Fig. 36 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.44\linewidth,clip]{Figures/wire_ypos_nominal}
\includegraphics[width=0.44\linewidth,clip]{Figures/wire_ypos_fitted}
%
\caption{Residual distributions of the wire coordinates in y direction with respect to the
nominal (left) and to the fitted (right) wire grid from the cosmic ray measurements. The widths of the
distributions include the measurement errors.}
\label{fig_wire_ypos}
% 
\end{center}
\end{figure}

\vspace{5mm}

%
% --- Fig. 37 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.44\linewidth,clip]{Figures/layer_zpos_nominal}
\includegraphics[width=0.44\linewidth,clip]{Figures/layer_zpos_fitted}
%
\caption{Residual distributions of the layer-to-layer distances in z direction with respect to the
nominal (left) and to the fitted (right) wire grid from the cosmic ray measurements. The widths of the
distributions include the measurement errors.}
\label{fig_layer_zpos}
% 
\end{center}
\end{figure}




%% --------- B3.4 -----------------------------------------------------------
%%
\subsubsection{Interfacing with the readout electronics}
\label{Interfacing}
%%
%% --------------------------------------------------------------------------

The readout and high-voltage supply scheme follows closely the one of the present MDT chambers
using the same parameters and specifications. The high-voltage decoupling capacitors on the readout
side and the terminating resistors on the high-voltage supply end are individually encapsulated in
plastic containers for high-voltage protection. The plastic containers are integrated with the
hedgehog cards plugged onto the gold-plated pins of the signal caps and ground connectors. The
ground pins are screwed into the gaps formed by three adjacent tubes 
%% (see Fig.~\ref{fig_groundpin})
during chamber assembly to connect the tube walls to the ground of the hedgehog cards
(Fig.~\ref{fig_hedgehogs}. This scheme allows for the high-voltage-free design of the readout
hedgehog cards. 

Each passive readout hedgehog card is connected to an active front end electronics board (mezzanine
card) for 24 channels  carrying new radiation hard ASICs, three 8-channel
amplifier-shaper-discrimiator (ASD) chips and one 32-channel HPTDC chip  (see below). The mezzanine
cards follow one-to one the shape of the hedgehog cards and are already under development. The
electronics boards are enclosed in chromatized aluminum Faraday cages which also shield the readout
hedgehog cards against the mezzanine cards.  


%
% --- Fig. 38 ----------------------------------------------------------------
%

\begin{figure}[!htb]
\begin{center}
\vspace{5mm}

\includegraphics[width=0.36\linewidth,clip]{Figures/hv_hedgehog} 
\hspace{1mm}
\includegraphics[width=0.36\linewidth,clip]{Figures/signal_hedgehog} 
\hspace{1mm}
\includegraphics[width=0.22\linewidth,clip]{Figures/Small_tubes_w_elx}  
 
\caption{High voltage (left) and signal (middle) distribution boards, the ''hedgehog cards'', to be
		 mounted at the two ends of the tubes (right). The plastic cylinders containing the
		 decoupling capacitors and the terminating resistors, respectively, are integrated on the
		 PCB boards.}

\label{fig_hedgehogs}
%
\end{center}

\end{figure}


%% ---------- B3.4 ----------------------------------------------------------
%%
\subsubsection{Sharing of work and logistics between production sites}
\label{Splitting_of_work}
%%
%% --------------------------------------------------------------------------

The construction of the 96 drift tube chambers with approximately 70000 drift tubes of lengths
between 0.5~m and 2.2~m for the new Small Wheels can be performed at three main construction sites, 
the MPI Munich, the University of Freiburg and IHEP Protvino, in the years 2013 to 2016. 
The intergration of the sMDT and trigger chambers at CERN will proceed in parallel. 
With additional institutions joining the project, the
chamber construction can proceed faster. 2-3 FTE manpower per construction site are planned for the
chamber construction. 

LMU Munich and the University of W\"urzburg will contribute to the testing of drift tubes and
completed chambers before and after shipment to CERN as well as to chamber integration and
commissioning of the Small Wheels at CERN. The relative wire positions of all sMDT chambers and the
positions of the alignment sensors relative to the wires will be
measured with an accuracy of about 5 $\mu m$ in the cosmic ray test stand at LMU Munich like for
the ATLAS BOS and BOF MDT chambers built in Munich and for the sMDT prototype chamber (see below). 
A cosmic ray test stand will also be set up at CERN 
for the test of the integrated chamber modules before installation. The measurement of the sMDT wire 
and alignment sensor positions also in this test stand, with two MDT chambers with known wire positions
as reference like in the setup at LMU Munich, is under consideration. In both test stands also the
relative positions of sMDT and trigger chambers and of the internal geometry of the trigger chambers 
can be measured with high accuracy. 

The participating institutes have extensive experience with the construction of the ATLAS MDT
chambers as well as the associated quality assurance procedures. The required clean rooms and test
equipment and the design of tooling for chamber construction and testing already exist. The
University of Freiburg and MPI Munich will also be involved in the design, fabrication and
measurement of the alignment reference bars for the new Small Wheels in collaboration with Brandeis
University.


%%% ==== B4 ============================================================
%%%
\subsection{Quality Assurance and Commissioning}
\label{Quality_Assurance}
%%%
%%% ====================================================================

\if{0}

{\it

  \begin{enumerate}
  \item Quality assurance of all individual chamber parts, include
    necessary manpower and rate of tests
  \item Quality assurance and commissioning scheme of full chambers,
    include necessary manpower and rate of tests
  \item How can/is data of the commissioning used later (e.g. strip or
    wire positions)?
  \end{enumerate}

  Note: A common commissioning strategy during and after assembly of
  the wheels will be given in a previous chapter
}

\fi

The quality assurance and commissioning procedures follow closely the specifications for the ATLAS MDT
chamber production~\cite{ref_qadoc}. Each tubes will be tested with respect to
wire tension, gas tightness and leakage currents under high voltage before installation in a chamber. 
The full quality control procedures have already been developed and tested during the sMDT prototype chamber
construction. 
Due to the new design of the endplugs and of the chamber assembly tooling, 
wire position measurement for individual drift tubes and monitoring of the tube positioning 
during assembly, as performed during the ATLAS MDT chamber production, are not necessary anymore
as was demonstrated by the sMDT prototype chamber construction.
 
The hedgehog cards and the mezzanine readout boards with the new radiation hard ASD and HPTDC chips
as well as the new chamber service modules CSM (see below) will be desiged, produced and tested by
MPI Munich.  New improved noise filters for the high-voltage supply lines for each chamber layer
have been designed and will be produced at MPI Munich.

The completed chambers will be tested for broken wires, gas tightness, leakage currents and noise
rate before and after delivery to CERN. In addition, all chambers will be tested in cosmic ray
test stands at LMU Munich and CERN. The individual wire positions of the sMDT chambers and the positions of the 
alignment sensors relative to the wires will be measured with an accuracy of about
5 $\mu m$ using two MDT chambers with known wire positions as reference as it was done sucessfully for all 
ATLAS BOS and BOF MDT chambers built in Munich and for the sMDT prototype chamber. 
The geometrical chamber parameters will be determined with submicron precision in this way. 

Bundles of drift tubes will be mounted on the alignment platforms 
in the same way as the alignment sensors themselves allowing for the precise direct determination of the sensor 
positions relative to the sMDT wires in the cosmic ray test stands. 
A method using stereo X-ray sources and calibrated references wires as developed at Brandeis University is also under
consideration for measuring the alignment sensor positions realtive to the sMDT wires.
After integration, also measurement of the positions of
the trigger chambers with respect to the wires in the drift tube chambers and of the internal geometry of the trigger chambers 
in the cosmic ray test stands is foreseen.  

2-3 FTE manpower at each of the 4 core production sites are planned for chamber testing and
commissioning.   


%%% ==== B5 ============================================================
%%%
\subsection{Operation, Maintenance and Safety}
\label{Operation}
%%%
%%% ====================================================================

\if{0}

{\it

  Describe in detail the impact of failures of single components (gas
  leak, HV breakdown, front-end electronics) on the 
  detector operation. Comment on possible built-in redundancy.\\

  Describe in detail the possible scenarios for maintenance on the
  detector and the exchange or repair of detector parts.\\

  Describe the risks associated with the technology during operation
  and maintenance (HV, maximum currents, flammable gas etc.)

}
\fi

Due to their robust design and the high quality assurance standards during construction and
commissioning, the ATLAS MDT chambers operate with very high reliability and data taking
efficiency. The same design, fabrication and testing procedures will be applied for the small
diameter drift tube chambers. Also maintenance and repair procedures will be the same in principle
as for the existing MDT chamber system with improvements in the access to the CSMs and the HV splitter boxes
as well as to the chambers in the inner regions of the new Small Wheels. 

The modular structure of the chambers provides a high degree of redundancy.
Each multilayer of a chamber will be supplied by a separate high voltage channel,
the innermost chambers by two channels because of the higher currents. 
384 HV channels are needed for both Small Wheels. 

In the chamber layout and the design of the Small Wheel structure, accessibility
of the Faraday cages of the drift tube chambers for exchange of electronics boards 
or for disconnecting individual drift tubes has been taken into account. 
The chamber service modules (CSM) together with the DCS boxes of all chambers will be installed in
better accessible and more radiation-safe regions at the outer rim of the Small Wheel.
There will be 2 CSMs per chamber, one per multilayer, such that only one multilayer is lost
until a broken CSM is replaced during an ultrashort access. 

%
% --- Table 10 -------------------------------------------------------------------
%

\begin{table}[!htb]

  \begin{center}
%   
    \begin{tabular}{|l|l|l|l|} \hline 

    Component        & Comment                     & Loss in coverage  & Recovery procedure   \\  
                     & (redundancy, accessibility) &                   &                       \\     
   \hline \hline 
    CSM (with        & 2 CSMs per chamber,         & 1 multilayer      & Repair in US access   \\   
    DCS box)         & 1 CSM per multilayer (ML)   &                   & CSMs at outer rim     \\
    \hline 
    Mezz. card       &                             & 24 chan.s in 1 ML & Repair in WS     \\
    \hline
    LV supplies      & 2 CSMs (in diff. chambers)  & 2 ML in diff. chambers& Repair in US access \\        
                     & per channel                 &                   &                       \\ 
    \hline 
    HV supplies      & $1-2$ channels per ML       & $0.5-1$ ML        & Repair in US access   \\
    \hline
    Broken wire      & HV distr. per layer using   & $0.5-1$ ML before,& Disconnect tube layer \\  
                     & splitters at SW outer rim   & $0.5-1$ layer after layer & in US access  \\       
                     &                             & disconnect        & Discon. tube from HV  \\
                     &                             &                   & Repair in WS          \\
   \hline
    Gas leaks        & 1 gas line per sect. and ML,& 1 ML of 1 sect. before, & Close valve of leaking \\  
                     & 1 valve per ML at outer rim & 1 ML of 1 chamb. after  & ML in US access  \\
                     &                             & closing valve     & Repair in WS          \\
   \hline
   \end{tabular}
   \caption{Risk analysis for the sMDT system in the new Small Wheels. 
            The redundancy and accesibility of the critical components 
            and the maximum loss in detector coverage in case of component failure 
			are given as well as the recovery procedures (US = ultrashort, WS = winter shutdown).}
			
	\label{riskanalysis}
  \end{center}
%
\end{table}

The individual tube layers are independently connected to the high-voltage. 
The splitter boxes for the HV channels will be located at the outer rim of the new Small Wheels. 
If a wire breaks, which is a very rare event, only one tube layer will be lost after disconnecting it 
from the HV splitter in an ultrashort access. During winter shutdown and opening of the Small Wheel, 
the affected tube can be disconnected from the high-voltage and the rest of the tube layer can be reconnected.

Gas leaks in the present MDT chambers are mainly due to cracks in injection moulded Noryl\textsuperscript{\textregistered}
endplugs and gas connectors. The drift tubes in the new Small Wheels are mechanically 
protected from the outside by the trigger chambers. To avoid gas leaks due to cracks in
endplug insulators and gas connectors, thermoplastics with much better robustness against cracking
than in te present MDT chambers have been chosen (see~\ref{Technical_Implementation}, above). 
In addition due to their smaller volume, the 15~mm diameter endplugs are less prone to mechanical stress and cracks in the
injection moulded plastic insulators than the 30~mm diameter endplugs.

The existing recirculating gas system with one volume exchange per day can be fully re-used. 
Each multilayer of a Small Wheel sector will be supplied separately with gas using 16 gas lines
for each new Small Wheel. Each multilayer of a chamber has a valve located at the outer rim of the Small Wheel.
The total gas volume of the sMDT chambers in one new Small Wheel is 6750~l, 4000~l less than for the
MDT chambers in one present Small Wheel. 

The risk assessment for the sMDT chamber system for the new Small Wheels is summarized in Table~\ref{riskanalysis} 
including the measures for minimizing the risk and reducing it even further than in the present Small Wheels.

 

%%% ==== B6 ============================================================
%%%
\subsection{Detector Performance}
\label{Performance_appendix}
%%%
%%% ====================================================================

\if{0}

{\it
  Describe in detail the performance of the detector, including
  results from test beam studies. Include studies with background
  radiation ($\gamma$, n, p)

  \begin{enumerate}
  \item Detector occupancy as function of rate
  \item Spatial and angular resolution as functions of rate and angle
    of incidence for single point measurements and segments
  \item Time resolution
  \item Efficiency (single measurement and segment)
  \item Double track resolution
  \item Rejection of fake and background tracks
  \item Sensitivity to background radiation
  \item Performance limits (maximum rate)
  \end{enumerate}
}
\fi

In order to verify the performance of the sMDT chambers, extensive
tests of the full-scale prototype chamber with 15~mm diameter drift tubes have been
performed in 2010 and 2011 in the H8 high-energy muon beam without background irradiation
(see Fig.~\ref{fig_prototype_H8}, left) and, using cosmic ray muon tracks, in the
CERN Gamma Irradiation Facility (GIF) with a 500~GBq ${}^{137}$Cs $\gamma$ source
(Fig.~\ref{fig_prototype_H8}, right). Standard ATLAS MDT readout electronics has been used
with the adjustable deadtime set to the minimum value corresponding to an overall effective
deadtime of 200~ns. The spatial resolution and the efficiency of the individual drift tubes 
have been measured for increasing $\gamma$ background counting rates up to 1200 kHz/tube 
at uniform illumination corresponding to 17~kHz/cm$^2$ in tubes of 0.5~m length like at the 
innermost radius of the new Small Wheels. 

%
% --- Fig. 39 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.35\linewidth,clip]{Figures/H8_photo} 
\hspace{2mm}
\includegraphics[width=0.60\linewidth,clip]{Figures/GIF_drawing} 
%
\caption{The test setups with the sMDT prototype chamber in the 
         H8 muon beam at CERN (left) and in the GIF 
         using a cosmic ray muon trigger (right).} 

\label{fig_prototype_H8}
% 
\end{center}
\end{figure}

As a measure for evaluating the tracking efficiency, we define the ''3$\sigma$-efficiency'' as the
probability of detecting a tube hit within a distance of 3 times the drift tube resolution $\sigma$
from the muon track, the muon track being defined by the other tubes on the track, extrapolated to
the active volume of the tube. Similarly, the drift tube resolution as a function of the drift  
radius is determined by an iterative method excluding the evaluated tube from the track
reconstruction in the chamber~\cite{ref_resolution_measurement}. 

%
% --- Fig. 40 ----------------------------------------------------------------
%

\begin{figure}[!htb] 
\begin{center}
\includegraphics[width=0.5\linewidth,clip]{Figures/efficiency_vs_rate} 
%
\caption{The $3\sigma$ efficiency of individual drift tubes as 
measured at the GIF as a function of the background counting rate. Results for 15~mm and 30~mm diameter tubes are compared. The
corresponding calculated track segment reconstruction efficiencies in 2 x 4 layer MDT chambers and in 
sMDT chambers with 2 x 6 or, optionally, 2 x 8 tube layers are also shown.}
\label{fig_efficiency_GIF11}
% 
\end{center}
\end{figure}



Fig.~\ref{fig_efficiency_GIF11} shows the 3-$\sigma$ efficiency of 15~mm diameter drift
tubes and the track segment reconstruction efficiency as a function of the
$\gamma$ background counting rate in comparison with the results for the 30~mm diameter tubes from previous
tests of a BOS MDT chamber at GIF with the X5 muon beam~\cite{ref_deile}, \cite{ref_horvat}.  
The measurements were performed using as 
external tracking reference the other drift tube layers of the prototype chamber and a
silicon strip detector beam telescope for the BOS chamber in the X5 beam, respectively.
At low background rates, the
$3\sigma$ tube  efficiencies of 30 and 15~mm diameter tubes are 94~\%. The
efficiency loss is due to $\delta$-rays created by interaction of the muons with the tube walls
which produce hits earlier than the muons. The degradation of the efficiency with increasing rate
shows the expected linear behaviour. The redundancy of track measurements in different tube
layers allows for a better than 99~\% track segment reconstruction efficiency up to the 
highest expected background rates at high-luminosity LHC.  

%
% --- Fig. 41 ----------------------------------------------------------------
%

\begin{figure}[!htb]
 
\begin{center}
\includegraphics[width=0.5\linewidth,clip]{Figures/resolution_measured_vs_simulated} 
%
\caption{Spatial resolution (with time-slewing corrections) as a function of the drift radius 
of large and small diameter drift tubes measured without background irradiation in the X5 and in 
the H8 muon test beam, respectively, in comparison with simulation results using GARFIELD.
Time-slewing corrections improve the average drift tube resolution by $20~\mu$ both for the 
larger and the smaller diameter tubes.}
\label{fig_resolution_H8_rdep}
% 
\end{center}
\end{figure}
%

In Fig.~\ref{fig_resolution_H8_rdep} the spatial resolutions of 15~mm and 30~mm diameter drift
tubes  measured as a function of the drift radius $r$ and without background irradiation 
in the CERN high-energy muon beams H8 and X5, respectively, are compared. 
The track impact radius was determined using 
as external references the other drift tube layers of the prototype chamber in the H8 beam and, respectively, 
a silicon strip detector beam telescope in the X5 beam.    
The radial dependence of the 15~mm diameter
tube resolution agrees with the 30~mm diameter tube resolution measurement for $r<7.5$~mm
and with the GARFIELD simulation~\cite{ref_garfield}.
The comparison of the resolution curves
is performed without time-slewing corrections applied.   
Corrections for time-slewing using the pulse-height information provided by the MDT readout electronics 
improve the average drift tube resolution by $20~\mu$ both for the 
larger and the smaller diameter tubes.
The average spatial resolution of the of 15 and 30~mm diameter
tubes at low background rates is $110\pm 2~\mu$m and $83\pm 2~\mu$m, respectively, taking into account the
time-slewing corrections (see Fig.~\ref{fig_efficiency_GIF11}).

The dependence of the spatial resolution of the 15~mm diameter drift tubes has been measured at the GIF
using the unirradiated regions of the prototype chamber as tracking reference for cosmic muons.
The measurements extended up to a background flux of 10 kHz/cm$^2$ at which an average drift tube resolution
of $143\pm 4~\mu$m has been obtained. At 14 kHz/cm$^2$ rate it will still be better than $170~\mu$m
(see Fig.~\ref{fig_dtresolrate}).
 
%
% --- Table 11 -------------------------------------------------------------------
%

\begin{table}[!htb]

  \begin{center}
%   
    \begin{tabular}{|l|c|c|c|r|} \hline 


    Component                    & Nr. of units   & Cost/unit  &Total cost      \\  
                                 &                & {\it (CHF)}&{\it (kCHF)}    \\  \hline

    Al tubes                     &  71000         & 3.6     &  256 \\
    Wire                         & 5.5~km         & 488/km  &    3 \\
    Endplugs                     & 141312         & 7.2     &  791 \\
    Gas connectors               & 141312         & 1.8     &  113 \\
    Spacer, supports             &    96          & 1000    &   96 \\    
    Faraday cages                &  2 x 96        &  500    &   96 \\                     
    Tooling                      &     2          & 25000   &   50 \\ 
   \hline
    Detector mechanics           & \multicolumn{2}{|c|}{}   & 1405 \\
   \hline

    HV\&RO hedgehog boards       & 5888           & 100     & 589  \\
    Mezzanine cards w. cable     & 2944           & 240     & 706  \\ 
    CSMs                         & 160+32         & 1100    & 211  \\
    MRODs/CSM                    & 160            & 1200    & 192  \\   
   \hline
    Electronics\& readout        & \multicolumn{2}{|c|}{}   & 1698 \\
   \hline

    Gas distribution system/ML   & 2 x 96         &  300    &   58 \\
    LV\&HV power supplies        & 160            & 2000    &  320 \\ 
    w. cables/CSM                & & & \\
    DCS modules w.\ fiber link/CSM & 160          & 400     &  64  \\
   \hline
    Services                     & \multicolumn{2}{|c|}{}   & 442  \\
   \hline
    In-plane sensors/chamber     &  96            &  909    &   87 \\
    External alignment sensors   & 4 x 96         &  455    &  175 \\
    Multiplexers/chamber         &  96            &  455    &   44 \\   
   \hline
    Alignment (on-chamber)       & \multicolumn{2}{|c|}{}   &  306 \\ 
   \hline\hline
    Total                        & \multicolumn{2}{|c|}{}   & 3851 \\
   \hline 
    \end{tabular}
   \caption{CORE cost of the sMDT chamber system including services, 
            readout and alignment components.\label{sMDT_cost}}
  \end{center}
%
\end{table}

%%% ==== B7 ============================================================
%%%
\subsection{Aging Tests}
\label{Aging_appendix}
%%%
%%% ====================================================================

\if{0}

{\it

  Describe in detail results from aging tests for all components, the
  detector itself including the on-chamber gas distribution, read-out
  and/or trigger, alignment, and detector control electronics.

}

\fi

Aging is not expected to occur in aluminum drift tubes with clean Ar:CO$_2$ gas.  No aging has been
observed in test of the MDT tubes up to a collected charge  on the wire of 0.6~C/cm. Only endplug and
gas system materials with little outgassing which have already been certified for the ATLAS MDT
chambers are used and strict cleaning procedures are applied for all components in order to
prevent contamination of the drift gas. There esists extensive experience on material selection and cleaning
procedures from the ATLAS MDT chamber construction and commissioning.  

Aging tests of the new drift tubes with a 25 MBq and a 200 MBq $^90$Sr source are in progress.
Until 27 January 2012, 1.38 C/cm of charge has been accumulated on the wires without sign of aging.
With the 200 MBq source, currently 0.025 C/cm are accumulated per day
at a current of $3.1~\mu$A per tube.

 
   
%%% ==== B8 ============================================================
%%%
\subsection{Cost, Funding, and Manpower}
\label{Cost_appendix}
%%%
%%% ====================================================================


\if{0}

{\it

  \begin{enumerate}
  \item Table of cost of each component, full chambers and total
  \item Additional costs (e.g. integrating two technologies)
  \item Arrangements for funding (if any so far)  
  \item List of manpower needs, especially include statements on the
    the current and future availability of experts (for at least the
    full construction and commissioning period, i.e. 2012 -- 2019,
    better also for the operation)
  \end{enumerate}
    
}
\fi

The costs of chamber mechanical components, on-chamber electronics, power supplies and DAQ system 
are summarized in Table~\ref{sMDT_cost}. The cost estimates are based on tenders as well as on the
actual cost  figures of the ATLAS MDT chamber components. 

Manpower cost for chamber assembly and test and for the testing of the electronics boards is not
included The manpower allocation foreseen for this work at the participating institutes is shown in
Table~\ref{sMDT_manpower}. The infrastructure of climatized clean rooms and the cosmic ray chamber
test facility already exist as well es experienced technical personell. The design of the chambers
and of the assembly tooling is performed at MPI Munich. The signal and high-voltage distribution
(hedgehog) boards, the readout (mezzanine) cards, the amplifier-shaper-discriminator (ASD) chip and
the chamber service module (CSM) are already under development  at MPI. 

%
% --- Table 12 -------------------------------------------------------------------
%

\begin{table}[!htb]

  \begin{center}
%   
    \begin{tabular}{|l|c|l|} \hline 

    Institute & FTE & Contribution  \\  \hline

    MPI Munich    & 5    & Mechanics, electronics, L1 trigger design \\
                  & 7    & Chamber construction, test, integration, installation, \\
                  &      & alignment system, electronics production, HV/LV system \\   
    LMU Munich    & 3-4  & Chamber construction, test, integration, installation \\
    Freiburg U.   & 5-6  & Chamber construction, test, integration, installation, \\
                  &      & gas system, DCS, alignment system \\      
    W\"urzburg U. & 3    & Chamber, electronics test, integration, installation, \\
                  &      & HV/LV system \\ 
    IHEP Protvino &      & Chamber construction, test, installation \\ 
    NIKHEF        &      & MRODs design, production, test, installation \\
    Tokyo         &      & L1 trigger and electronics design and implementation \\
    Brandeis U.   &      & Alignment system \\
      
   \hline 
    \end{tabular}
   \caption{Manpower for sMDT design, production, integration and installation.}

   \label{sMDT_manpower}

  \end{center}
%
\end{table}


%
% --- Table 13 -------------------------------------------------------------------
%

\begin{table}[!htb]

  \begin{center}
%   
    \begin{tabular}{|l|c|c|c|c|c|c|c|c|} \hline 

    Item                   & 2012 & 2013 & 2014  & 2015 & 2016 & 2017 & 2018 & Total \\  
	\hline
    Detector mechanics     &  100 &  400 &   500 &  405 &      &      &      & 1405  \\
    Electronics\& readout  &      &  200 &   400 &  500 &  406 &  192 &      & 1698  \\
    Services               &      &      &       &   64 &  150 &  228 &      &  442  \\
    Alignment (on-chamber) &      &   70 &    80 &   80 &   76 &      &      &  306  \\  
   \hline
    Total                  &  100 &  670 &   980 & 1049 &  632 &  420 &      & 3851  \\
   \hline 
    \end{tabular}
   \caption{CORE cost time profile for the sMDT chambers (kCHF).\label{sMDT_profile}}
  \end{center}
%
\end{table}

A close collaboration exists between the MDT institutes and the TGC as well as the RPC institutes
on integrated chamber design and layout and on a common test program at the GIF and the H8 test
beam.  

%
% --- Table 14 -------------------------------------------------------------------
%

\begin{table}[!htb]

  \begin{center}
%   
   \begin{tabular}{|l|l|} \hline 
   
   Time of completion & Task \\
   \hline 
   2010     & sMDT Chamber design, prototype construction and test \\
   2011     & Integration sMDT amd trigger chambers, \\
            & full ASD FE chip (4 channels) \\
   2012     & Construction of sMDT chambers for elevator regions, \\
            & NSW design and chamber layout, \\ 
            & full 8-channel ASD chip \\
   2014     & CSM design incl. MDT based L1 trigger functionality \\ 
   2013--16 & Chamber construction and integration, electronics production \\
   2017--18 & Integration and installation of NSWs at CERN \\
     
   \hline 
   \end{tabular}
   \caption{Time schedule for sMDT chamber development amd 
            construction.\label{sMDT_schedule}}
  \end{center}
%
\end{table}

A large fraction of the funding of the sMDT system is expected from the German funding agency
BMBF and from MPI Munich in the period 2012--2016. The funding request to the BMBF for the period
2012--2015 has been submitted in December 2011. NIKHEF has expressed interest
to contribute the MRODs for the sMDT chamber readout. Brandeis University and the University of Freiburg plan to
contribute the optical alignment system including the alignment reference bars. The
expected CORE cost spending profile is given in Table~\ref{sMDT_profile}, the time schedule
for development and construction in Table~\ref{sMDT_schedule}.
