%%%%%  The following statement gives section #5 to the MDT-TGC,
%%%%%  independent of the number of previous sections
%
\setcounter{section}{4}
%
\newpage

\section{Detector concept 1 :  MDT + TGC  (working title)}

{\it Introduction to this concept:
This section should describe the technology concept, details 
up to the level of a single chamber should be given in the appropriate
appendix.}

\subsection{Introduction}

To cure the shortcomings of the existing system, a new concept is proposed for the
Inner station, the New Small Wheel (NSW). For the trigger chambers we propose to
maintain the basic operating concept of TGC chambers, complementing them with a new,
high-performance readout system.  The pulseheight distribution of signals induced
into the strips of the TGC cathodes (measuring $\eta$) are convoluted to give the
precision coordinate with an accuracy of $ < $100 $\mu m$. With modern,
radiation-tolerant FPGAs the location of the hits can be determined fast enough for
the L1 trigger. In the proposed detector layout, a package of 4 TGC chambers is
placed in front and behind the MDT chambers, each. A TGC package will contain 4 wire
layers (wires running radially, perpendicular to the strips), 4 cathode layers for
centroide finding and another 4 cathode layers segmented into pads for fast selection
of a Region of Interest (RoI). In the offline analysis the pads will be an important
tool for resolving ambiguities in the x-y pairing of coordinates, when more than one
track is present in a chamber. With a distance of about 300 mm between the TGC
packages in front and behind the MDT, an angular resolution of $< 0,3$ mrad can be
achieved. Only tracks pointing to the interaction point will be considered as
high-p$_T$ candidates for the L1 trigger. A detailed presentation of the method is
given in section~\ref{chapter:TGC}.

The problem of high tube occupancies of the MDT is solved by using a newly developed
type of MDT drift tubes, the tube diameter being reduced from 30 mm to 15 mm. While
the tube area exposed to background radiation is thus reduced by a factor of two, the
maximum drift time is reduced by a factor of 3,5 (750 ns to 200 ns), the combined
effect giving a reduction of hit rates by a factor of 7. The mechanical structure and
the alignment system will be as similar as possible to the ones in the present SW
architecture. Like in the case of the TGCs, faster readout electronics has to be installed, see
section~\ref{chapter:MDT_electronics}.

Both new chamber systems, the TGCs and the MDTs, can be operated with the same chamber gas
as in the present system. Power requirements for the electronics of both systems will be
higher due to higher channel count. Whether this requires active cooling, as is now used
for the electronics of the CSC chambers in the region $\eta$ $>$ 2 is under study. Aim is
to have services arranged in such a way as to be able to use the existing service
infrastructure like e.g. the cable Schlepps.

\subsection{Detector technology and layout}

{\it
    Description of detector concept (a detailed description of the
    working principle of each detector should be given as an
    appendix).\\
    If more than 1 technology is used motivate the decision and detail
    how they work together (e.g.\ can services be shared, is the
    information of the trigger chambers used in the precision
    chambers, how are combined chambers assembled etc.)
	
    List of all operating parameters\\
    Detailed layout: acceptance, description of chamber overlap
    and dead areas, drawings\\ 
    Tables with chambers sizes, number of channels\\
    Internal alignment scheme (the overall common endcap alignment scheme
    is described in the previous chapter)\\
    Calculations about mechanical stability and expected
    deformations due to gravity, temperature changes, (magnetic field) etc.\\
    Requirements for mount points\\
    Details of service points and other positions where access is needed\\
    Concept for chamber replacement (what needs to be dismounted etc.)
}

\subsubsection{Detector technology of the TGC chambers}

Text about TGCs.

\subsubsection{Detector technology of the MDT chambers}

The outer region of the ATLAS detector, where the muon chambers are located, receives 
high rates of low-energy neutrons, mainly due to shower leakage from calorimeters and 
shielding structures in the high-$\eta$ region.  At the nominal luminosity, gammas from 
neutron capture and related conversion electrons are expected to generate hit rates in 
the range 50--300 kHz in each MDT tube. A conversion electron may create an inefficiency 
if the signal arrives {\it before} the muon signal. The muon detection efficiency thus 
becomes exp(-$\tau\times$f) $\approx$ 1-$\tau\times$f, where $\tau$ is the average drift 
time in the MDT tubes and f the hit rate due to gamma conversions.

%% --- Fig.  1 ---------------------------------------------------------------------
%
\begin{figure}[h]
\begin{center}
\includegraphics[width=0.35\linewidth,clip]{Figures/Large_small_tubes}
\label{Large_small_tubes}

\caption
{The tracking quality in 30 mm and 15 mm drift tubes in a region of high n/$\gamma$
background. The occupancies from background hits (red dots) are 50\% in
the 30 mm tubes but only 7\% in the 15 mm tubes due to shorter drift time and smaller 
area.
}
%
\end{center}
\end{figure}

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

At high rates of n/$\gamma$ background, the efficiency may be further reduced by a 
decrease of the gas amplification due to space charge from slowly drifting positive ions 
in the tubes, while the {\it fluctuations} of the space charge tend to degrade the 
spatial resolution by up to about 20 \% at the highest rates.

The effects of gamma conversions in the MDT tubes have been studied in detail using a 
muon beam in the presence of intense $\gamma$-irradiation of up to $500\,$Hz/cm$^{2}$ 
(i.e. $\sim$300 kHz/tube), as delivered by the Gamma Irradiation Facility at CERN 
(GIF)~\cite{mdt_highrates}. While the $\gamma$-rates at the GIF correspond to only about 
30 \% of the background levels expected for the hottest regions at the SLHC, the results 
of these measurements already allow to define the baseline of a chamber design with much 
improved tracking capability: MDT drift tubes with only half the tube diameter offer a 
reduction of the drift time by a factor 3.5, due to the non-linear relation between track 
distance from the central wire and drift time (r-t relation) and in addition by a factor 
2 from the exposed area, thus yielding a factor 7 in the reduction of the hit rate due to 
n/$\gamma$ background. Moreover, up to two times more tube layers can in principle be 
accommodated in the available space, leading to improved track finding efficiency and 
position resolution (see Fig.~\ref{Large_small_tubes}).

%% Fig. 2 ------------------------------------------------------------------------ 

\begin{figure}[h] 
\begin{center} 
\includegraphics[width=0.4\linewidth,clip]{Figures/Large_small_efficiency} 
% 
\caption{Efficiency vs. hit rate per tube for 30 mm and 15 mm drift tubes.} 
\label{Large_small_efficiency} 
% 
\end{center} 
\end{figure} 

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

The reduction of the tube diameter of the MDT tubes allows to maintain the main 
advantages of the drift tube concept:

(a) independence of the position resolution from the angle of incidence onto the chamber 
plane (contrary to drift chambers with rectangular drift geometry)

(b) operational independance of each tube, where the malfunction of a tube can only 
generate a negligible inefficiency

(c) modularity of chamber construction.

To verify the performance of 15 mm (''small'') tubes, a number of tests was executed, 
using cosmic muon tracks. A pair of 30 mm (''large'') drift tube chambers was used as 
reference, defining the position of the muon track, while a layer of small tubes was the 
device under test.  Tubes along the track are called 'efficient' when the hit is detected 
inside a 3$\sigma$ road, as defined by the reference tubes.

This measurement was done in the presence of adjustable levels of gamma background due to 
the GIF facility at CERN~\cite{mdt_slhc}. Fig.~\ref{Large_small_efficiency} shows the 
efficiency of small and large tubes vs. hit rate from gamma conversions. As expected, 
small tubes provide a much better performance at high background rates.  The efficiency 
at rate zero deviates from 100 \% due to tracks passing across or close to the tube walls 
and due to $\delta$-electrons shifting the hit position outside the 3$\sigma$ acceptance 
road. The average position resolution in the small tubes was about 120 $\mu$m.  Due to 
the short drift compared to large tubes, this value showed little dependence on the 
background rate.

%% =======================  section 5.3  ======================

\subsection{Performance}

{\it
  Summary of chamber performance, details in appendix of technology. 

  Spatial and angular resolution as functions of rate and angle of incidence\\
  Time resolution\\
  Efficiency (single measurement and segment)\\
  Double track resolution\\
  Rejection of fake and background tracks\\
}

%% =======================  section 5.4  ======================

\subsection{L1 trigger and electronics}
\label{chapter:TGC}
{\it
  How the L1 signal are produced, starting from the detector signal
  till the formation of SL input.\\
  Latency (calculation, measurement with demonstrator)\\
  Compatibility with Phase II upgrade    RR to supply text !!! \\
}

%% =======================  section 5.5  ======================

\subsection{Readout electronics and integration in DAQ}
\label{chapter:MDT_electronics}
{\it
  Detailed description of electronics chain.-- Integration to DAQ (Mention the GBT?).--
  Readout related parameters, e.g. bandwidth requirements, number and granularity of 
  read-out links.-- Compatibility with Phase II upgrade.
}

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.

\subsubsection{Architecture of the present MDT readout}

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}.

%% Fig. 3 ---------------------------------------------------------------------------
%
\begin{figure}[!htb]
%
\begin{center}
%
\includegraphics[width=0.50\linewidth,clip]{Figures/MDT_electronics_scheme_old}

\caption{Schematic diagram of the present MDT readout chain. 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, corresponding to 432 tubes, 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}

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

\subsubsection{Architecture of the readout for MDTs with Small tubes}

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.

%% Fig. 4 ---------------------------------------------------------------------------
%
\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}

%% ---------------------------------------------------------------------------------
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.

\begin{itemize}
  \item The ASD is re-designed in the IBM 130 nm technology. A 4-channel prototype,
  demonstrating the analog parameters, has already been produced and works correctly.
  Most analog parameters of the previous design are preserved.
   
  \item 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 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 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{itemize}

%% Fig. 4  -------------------------------------------------------------------------

\begin{figure}[!htb] 

\begin{center}

\includegraphics[width=0.85\linewidth,clip]{Figures/print_summary_15_08_2011}

\caption{
Three performance parameters for the 15 mm MDTs as a function of the tube hit rate. Red
curve: efficiency, assuming a dead time of 200 ns (equal to the maximum drift time) after
each hit. Blue: Saturation of the data link from TDC to CSM. Purple: Saturation of the
link from CSM to ROD. The links have a useful bandwidth of 80 Mbit/s and 1,4 Gbit/s,
respectively. Both have a base load of about 15\% due to the overhead of the transfer
protocol.
}

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

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

%% Fig. 5  -------------------------------------------------------------------------

\begin{figure}[!htb] 

\begin{center}

\includegraphics[width=0.35\linewidth,clip]{Figures/Small_tubes_w_elx}

\caption{
Space requirements at the tube ends on the Small tube chambers necessitate a separation of the
HV-coupling capacitors from the signal routing card (''hedgehog card''). The HV capacitor is mounted
in a small Noryl (??) cylinder.}


\label{Small_tubes_w_elx}
\end{center}
\end{figure}

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

Another stringent requirement for the practical 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{itemize}

  \item 
  HV decoupling capacitors are located in 15 mm diameter cylinders at the tube ends, see
  Fig.~\ref{Small_tube_structure}and Fig.~\ref{Small_tubes_w_elx}. 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 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 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.
  
  \item 
  While the power dissipation of the on-chamber frontend electronics of the present
  system was xx W/channel, leading to a dissipation of yy W/m in multilayers with 4 tube
  layers, the dissipation would now be about zz W/m. This may require flushing with dry
  air or even liquid cooling, as natural air convection is hampered by the tight space
  constraints of the Small Wheel.

\end{itemize}

Now something about mechanics, real estate, component density, packaging etc.

Finally something about rates.


\subsection{Services, infrastructure, and DCS  !!! RR+JD to supply text !!!}

{\it
  \begin{enumerate}
  \item Description of service scheme (including power system,
    read-out, trigger, alignment), cooling needs and other special
    requirements
  \item Table with number of services (number of cables, outer
    diameter, cross section of leads)
  \item Table with power consumption (per channel, chamber, total)
  \item Required rack space 
    \begin{enumerate}
    \item UX15 (include maximum allowed distance to detector if any) 
    \item US15 (power system)
    \item USA15 (DAQ)
    \end{enumerate}
  \item Gas system and distribution\\
    Details on number of gas manifolds per sector (include drawings)
    and connections to chambers (serial, parallel?)). Size of pipes\\
    Required nominal, minimum, and maximum flow\\
    Required precision of gas mixture\\
    Safety measures in case of inflammable gas\\
    Required rack space for gas system in SGX1, USA15, UX15
  \item Integration in DCS system, requirements for DCS !!!  Via GBT or ELMB++ ?? !!!
  \end{enumerate}
}

  \begin{table}
    \centering
    \begin{tabular}{lccc}
      Cable & Number of cables & Outer cable & Cross section\\
      & (granularity) & diam. (mm) & of leads (mm$^{2}$))\\
      \hline
      HV & & & \\
      LV & & & \\
      Monitoring and control & & & \\
      Front-end links & & & \\
      Calibration & & & \\
      Alignment & & & \\
      Miscellaneous & & & \\
      \hline
    \end{tabular}
    \caption{Example table number of services per chamber}
    \label{tab:services}
  \end{table}


  \begin{table}
    \centering
    \begin{tabular}{lccc}
      Chamber & Number of channels & Power consumption per channel &
      Total power consumption\\
      \hline
      & & & \\
      \hline
    \end{tabular}
    \caption{Example table: Number and types of chambers per sector}
    \label{tab:sector_type}
  \end{table}

%%% Sample tables commented out on 22.07.11 RR

\if{0}

Now comes a first example of a table 

  \begin{table}
    \centering
    \begin{tabular}{lrr}
      Micromega/TGC/RPC/MDT & Type 1 & Type 2\\
      \hline
      Number of chambers & & \\
      Radial extension (mm)& & \\
      Minimum length in $\phi$ (mm)& & \\
      Maximum length in $\phi$ (mm)& & \\
      Thickness in z (mm)& & \\
      Mass (kg) & & \\
      Number of layers & & \\
      Number of channels & & \\
      \hline
    \end{tabular}
    \caption{Example table chamber types}
    \label{tab:chamber_type}
  \end{table}

Now comes a second example of a table 

  \begin{table}
    \centering
    \begin{tabular}{lrr}
      Chamber & Small sector & Large sector\\
      \hline
              &  put in      &  a number! \\
      \hline
    \end{tabular}
    \caption{Example table: Number and types of chambers per sector}
    \label{tab:sector_type}
  \end{table}

\fi

