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\hspace{15cm} v1 \\



\vspace{3cm}

\begin{center}
\LARGE{ \bf ATLAS muon chamber construction at NIKHEF}



\end{center}

\vspace{1cm}



\large{NIKHEF ATLAS MUON GROUP}

 
\large{Contact: Marcel Vreeswijk, h73@nikhef.nl} 

\vspace{4cm}

\begin{large}

{\bf Abstract:}
At NIKHEF (Amsterdam),  the largest muon chambers for the outer layer of the barrel ATLAS muon spectrometer have been constructed.
 At this facility, more than  40000 single drift tubes have been produced and 100 drift tube assemblies (muon chambers) have been constructed.
We report on the quality assurance of both single drift tube production and chamber assembly. This, together with the also presented results from  X-ray scans at CERN (Geneva) and results obtained in a dedicated cosmic ray test set-up, also part of the facility, demonstrates that the chambers fulfil ATLAS specifications.
\end{large}


\vspace{4cm}

\newpage





\newpage

\tableofcontents

\listoffigures

Photographs to be made:
\begin{itemize}
\item Endplug foto with its components
\item Wiring robot met aspects: lege buis, draadspoel, volle buis, QA
\item Granieten tafel.
\item Granieten tafel detail jigs
\item Granieten tafel detail suction
\item Granieten tafel detail RASNIK tower
\item Granieten tafel detail sphereholders
\item Granieten tafel detail spheres etc.
\item Granieten tafel guido laser
\item Chamber compleet
\item Chamber detail faraday cage
\item Chamber zonder faraday cage
\item Chamber HV cards
\item Chamber RO cards=Hedgehogs
\item Chamber mezzanine
\item Chamber RASMUX
\item Chamber TEMPERATURE DCS
\item Chamber CSM
\item Chamber all sevices
\item Chamber gas manifolds
\item Chamber gas jumpers
\item los hedgehog cars, HV cards, mezzanine, 
\item aligment stuff
\item Chamber als geheel
\item cosmic ray stand geheel en details DCS en kamers, trigger
\end{itemize}


Drawings to be made/searched:
\begin{itemize}
\item Tube with endplug drawing with twister
\item MDT measurement principle
\item stacking overview of chamber
\item tube gluing of tubes
\item granite table with jigs/components (indien al beschikbaar)
\item eventueel: stacking steps of chamber
\item uitleg sag adjustment
\item gas triplet
\end{itemize}

\newpage

\pagestyle{plain}
\setcounter{page}{1}

\section{Introduction}
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfxsize=14cm\epsffile{atlasdet.ps}}}
\end{picture}
\end{center}
\caption{\sl   
xxxxxxxxxxxxxxxxxxxxxxxxxxxATLAS DETECTOR met MDT ingetekend
}
\label{atlasdet}
\end{figure}


\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfxsize=14cm\epsffile{xxxx.ps}}}
\end{picture}
\end{center}
\caption{\sl   
xxxxxxxxxxxxxxxxxxxxxxxxxxxMDT principle
}
\label{mdtprinciple}
\end{figure}

To stand-alone measure muons that emerge with a transverse momentum of 1~TeV/c with an accuracy  $\frac{\sigma_{P_T}}{P_T}$=10\% is the most stringent requirement for the muon spectrometer of the  ATLAS experiment at the LHC. 
 This translates to 50\um uncertainty on the sagitta measurement in  the 2~Tm integrated magnetic field, provided by an air core toroid. 

The muon system in the barrel region ($\eta<1$)  is designed such that muon trajectories are measured by three muon chambers as illustrated in figure~\ref{atlas}. All three layers consists of an approximately equal number of small and
 large  type chambers. 
At NIKHEF (Amsterdam, The Netherlands) we constructed 100 'Barrel Outer Large'
 (BOL) chambers, including four spare chambers. 
 
Muons chambers consist of accurately assembled layers
 of alumnium drift tubes.
A drift tube has a diameter close to 3~cm and is closed by two end-plugs
that hold a 50~\um thick tungsten wire. Under operational conditions, the
tube is filled with an Ar/CO$_2$ mixture of 93\%/7\% and the wire is set
a potential of 3xxxxxx~V with repect to the grounded tube wall. When a muon
traverses the tube, it ionises the gas and the free electrons drift to
the wire, generating a signal. The Read-Out electronics
measure the arrival time of the signal above an adjustable threshold as shown
in figure~\ref{drifttubeprinciple}. The
arrival time, containing the actual drift time information, is offline used
to determine the drift radius based on a known relation between drift time
and radius. Earlier tests show that the  drift tubes under well-controlled 
conditions have single hit resolution of about 80\um (averaged over drift distance), see~\cite{TDR}. The muon chambers in ATLAS have each at 
least $2\times 3$ drift tube layers, providing sufficient 
drift radii to recognize and reconstruct a track segment with high accuracy.


The BOL muon chambers consists of two separate layers (multi-layers), each with three drift tube layers, mounted on an aluminium support structure (spacer)
 as shown in figure~\ref{bol}.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=fmmdtch1.epsi,height=8cm,angle=-90}}}
\end{picture}
\caption{\sl Schematic view of a muon chamber.}
\label{bol}
\end{figure}
Physical deformations of the chambers during construction, transport 
and operation are monitored \footnote{For this reason the ATLAS muon chamber are called Monitored Drift Tube (MDT) chambers} with an integrated, 
so called 'in-plane', alignment system also indicated in figure~\ref{bol}.

The combination of the uncertainties on single hit resolution, alignment
and mechanical precision of the chambers should not exceed 50~\um to meet
the aforementioned accuracy on the sagitta measurement. 
Simulations have indicated that is is required to construct the chambers with
a mechanical precision of 20\um (RMS), which is
of unprecented accuracy for such large detectors.

In this report, we describe the production of single tubes and completed
BOL chambers, moreover we present the results on the quality assurance
operations. Among the tests is the dedicated measurement in the X-ray 
tomograph at CERN of a limited number (roughly 10\%) of the BOL chambers.
 Finally, we summarise the muon chamber performance in the cosmic ray set-up
at our facility.




\section{Coordinate systems}
 When the chamber is located on the granite table in the 'upward' position
 the local chamber coordinates are defined such that  the $y$ coordinate points to the sky, the $x$ coordinate runs along the tubes in the horizontal plane.
 The $z$ coordinate, the precision coordinate, runs perpendicular to the tubes.
 The $x$, $y$ and $z$ axis constitute a left-handed coordinate system.
The global coordinate system in our cleanroom is then defined by a south-north and  west-east direction that runs in the $x$ and $z$ direction respectively.
In the 'upward' position, the Read-out (RO) and High-Voltage (HV) side of the chamber coincides with the south and north respectively. 
In addition, for engineering purposes, we defined the west side of the setup as the 'reference-side'. The reference side always coincides with the smallest $z$ coordinate of the chamber.



\section{Drift tubes}
A schematic view of a drift tube is shown in figure~\ref{tube}.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=8cm \epsffile{tube.eps}}
\caption{\sl
Schematic view of a drift tube.  Several components are indicated.
}
\label{tube}
\end{center}
\end{figure}
A drift tube has a diameter of 29.970~$\pm$~0.015~mm and a wall thichness of 400~\um.
 The tube is swaged on two precise end-plugs that are manufactured with a
 precise outer ring of aluminium to position the tube during the assembly in
 jigs with high precision.   The end-plug also connects to the gas system and
 is closed by a signal cap  to connect  High Voltage (HV) and Read-Out (RO) electronics boards at the
 tube's HV and RO ends respectively.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=8cm \epsffile{endplug.eps}}
\caption{\sl
Picture of an end-plug and its components.
}
\label{plug}
\end{center}
\end{figure}



 The 50\um gold-plated tungsten wire is tensioned at 285~gram and then
 crimped into the end-plug. 
A locator ('twister') with  small gas flow resistance,
 accurately centres the wire with respect to its outer ring.

%The precision of the position of the wire near the tube ends
% is determined by the precision outer rings of the two end-plugs and
%he cocentrity of the wire locator. We aimed to manufacture and assemble
%the end-plugs with an accuracy on the wire better than  5\um. 


IETS ZEGGEN OVER BUIS EXTRUSION PROCES en/of STRAIGTNESS VAN BUIZEN????


\subsection{Drift tube requirements}
\label{tubereq}
The meet the 20\um precision requirement on the total chamber, the 
contribution of individual drift tubes has to remain below 10~\um. 
This imposes the accurate machining of the end-plugs and wire locators.
(which determine the position of the wire near the tube ends).
 Furthermore, to guarantee this precision over the full length of the chamber,
 the wires need to be tensioned within 285+-15gram with corresponding
 gravitational sag of 406+-22um. 
The requirement  on the co-centricity of the wire due to non-straightness
 of the drift tube (anode-cathode distance) is a second order effect and set at 100\um RMS.


Other than the mechanical precision we impose:
\begin{itemize}
\item
the dark current of individual drift tubes shall not exceed 10nA at 
3300V  at 3bar absolute pressure with an Ar/CO$_2$ (93\%/7\%) gas mixture
 (gas gain $2\times 10^4$), 
\item
the leak rate under these conditions must be less than $10^{-8}$ bl/s. 
\end{itemize}
These requirements ensure  long term  stable operation in the ATLAS experiment.



\subsection{Drift tube production}
The 40 thousand drift tubes were produced in the temperature-controlled
 cleanroom parallel to the assembly of the chambers, 
using a semi-automated wiring machine.
 On the picture shown in figure~\ref{wiremach}, taken at the north side (as we defined it),  several components are indicated.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=10cm \epsffile{wiremach.ps}}
\caption{\sl
OVERNIEUW MET ASPECTEN: LEGE HULZEN, EINDPLUGS, DRAADSPOEL, UITEINDELIJKE
BUIS.
Picture of the wire machine taken at the north side. Indicated are the
movable platform in the final position and the clamp to pre-tension the
 wire. Also indicated is the tube with has fixed end-plugs in this stage.
}
\label{wiremach}
\end{center}
\end{figure}

The machine is loaded by an aluminium tube and two complete endplugs.
 The wire is transported from its supply by means of airflow through the 'south' end-plug toward the 'north' end of the tube. 
At the north end the wire is literally sucked through the end-plug
and fetched by a wire clamp. Now, movable platforms at both sides bring
the end-plugs to their final positions in the tube.
 The two end-plugs are fixed by tube swager using air pressure. 
  At the south end, the wire is fixed at the left end-plug by crimping it and the tube is in the state as shown in the picture. 
The clamp at the other side moves away to pre-tension the wire by 400~gram before releasing it slowly to its final tension of 285 gram. 
Crimping the wire at the north end-plug finalises the drift-tube.

\subsection{Drift tube quality}
The  wire tension, length  and position was measured immediately after production for every tenth tube to assure proper operation of 
the wiring machine.

The tension is derived from the measurement of the fundamental harmonic 
resonance. This measurement is als used in~\cite{pavia} and it is based on
 the induced response to a sinusoidal current while the
tube is partially immersed in a magnetic field.

 The wire position with respect to the outer ring of the end-plug 
was measured  using an eletromagnetic method  (see \cite{emmi}). 
the method uses the response of two coils sensing the field of an sinusoidal current 
that is driven through the wire. One set of coils is used at each end of the tube and by rotating the tube by 90 degrees two projections (called $y$ and $z$)
for each end are obtained.

Figure~\ref{fig:wpos}a shows a scatter plot of these projections.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=yz.eps,height=10cm,angle=0}}}
\end{picture}
\caption{\sl
Scatterplot of the $y$ and $z$ deviation of the wire position measured on
a sub-sample of produced drift tubes.
}
\label{fig:wpos}
\end{figure}
 The radial deviation is better than 10\um (RMS) as appropriate. 
In these tests, we found only eleven tubes with a deviation larger  than 25\um in one of these projections, which we stored for further (destructive) studies.

 The gas tightness and dark current of all produced tubes was measured in a
 set-up (in the cleanroom) specially designed for this purpose
 (see appendix~\ref{app:slof}).
 This set-up consists of 80 vacumized large tubes (diameter 6xxxx~cm) loaded with the drift tubes under test. 
The drifttubes are filled with 4~bar 1\%/99\% helium/argon mixture and the wire is set at 3300~V.  
The leakrate (for Ar/CO$_2$ at 3~bar) and dark current measurement is
 shown in figure~\ref{fig:slofa} and~\ref{fig:slofb} respectively. 
The results indicate that the majority of the tubes is well within specifications. 
However, the long tail of the leakrate distribution (not shown) leads to a failure rate of about~1\%, making the leakrate the dominant rejection source.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=leak_logx.eps,height=10cm,angle=0}}}
\end{picture}
\caption{\sl Leakrate of all used tubes in b l/s }
\label{fig:slofa}
\end{figure}

\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=hv5.eps,height=10cm,angle=0}}}
\end{picture}
\caption{\sl a: Dark current in nA of
all used tubes. }
\label{fig:slofb}
\end{figure}


After ageing of at least one month and just prior to using the tubes in the actual chamber assembly,  all the tubes were subjected to a second
 wire tension test. Like the frist measurement, the tension is also
 derived from the measured resonance frequency, but without
the requirement that the tube is immersed in an magnetic field. 
The electrostatic force due to a supplied sinusoidal HV leads
 to mechanical wire oscillations. 
 The changing capacity of the tube is measured in an LC circuit, leading
to a resonance curve. the method is described in~\cite{kloe}.
For our wire with length 4940 mm  a weight per unit length of 38.70 mg/m,
a resonance frequency of $27.2\pm 0.5$~Hz corresponds to $285\pm 15$ gram 
tension.
 Only 21 tubes failed and the results for tubes that passed are shown in figure~\ref{fig:tens}.
 As mentioned above, for 10\% of the tubes a 'fresh' measurement of the wire tension is available, allowing to study 'slippage' that may occur over time. 
We expect that if any slippage occurs, it occurs dominantly in the
in the ageing period and possibly during handling of the tubes.
// No evidence for wire slippage was found.
The change in resonance frequency exhibits an assymetric
shape  as  shown in figure~\ref{dtens}. This suggest a comfortably
small wire slippage for a fraction of the tubes. 
%The results
%are presented in the scatterplot shown in figure~\ref{fig:tens}b.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=tens2.eps,height=10cm,angle=0}}}
\end{picture}
\caption{\sl Measurement of the wire tension of all tubes 
just before chamber
assembly.
% b: Scatterplot of the tension measured immediateley after production
%and just before chamber assembly for a sub-sample of the tubes.
}
\label{fig:tens}
\end{figure}
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=dtens.eps,height=10cm,angle=0}}}
\end{picture}
\caption{\sl Measurement of the change in wire tension between production
of the tube and chamber assembly.
% b: Scatterplot of the tension measured immediateley after production
%and just before chamber assembly for a sub-sample of the tubes.
}
\label{fig:dtens}
\end{figure}

In total, we have produced about 40000 drift tubes. 
Our stringent criteria led to a rejection rate of 2.5\%.
The 100 BOL chambers (96 ATLAS chambers and 4 spares)  we produced, contain 38448xxxxxxx tubes that fullfil our requirements.

% The sag of the chambers is adjusted, depending on their orientation
% in ATLAS,  such that the wires are centered with respect to the tubes
% with an RMS of 100\um.

\section{Drift tube chambers}
Above we already showed in figure~\ref{bol}  the mechanical layout of a BOL
 chamber. 
 The aimed mechanical precision of 20\um RMS is implemented as follows. 
Any transverse cross section of any chamber can be represented by a single
 wire grid.   The individual wires of a particular chamber are mapped on this
 grid with residuals distributed within 20\um RMS. Note that this precision
applies to the wires, while the tubes have a looser position requirement
of 100~\um RMS (with respect to the wire). 

The BOL chambers have a length of 5~m and come in three different widths: 
2160~mm (72 tubes/layer), 1680~mm (56 tubes/layer) and 1440~mm (48 tubes/layer), all with two multilayers with 3 tube layers on each side of the spacer.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=xxxx.ps,height=5cm,angle=-90}}}
\end{picture}
\caption{\sl stacking drawing+gluing }
\label{stacking}
\end{figure}
The spacer is constructed of  three 'I' beams, called cross-plates,
  running orthogonal to the tubes. The cross-plates have low mechanical
precision (0.5~mm) and the glue (3M xxxxxxxxx), which connects to the mulilayers, absorbs possible irregularities.
 The crossplates are themselves connected by two beams, that run longitudinal
 (which are therefore called long-beams). The horizontal position of the
central cross-plate with respect to the long-beams is adjustable to
compensate for gravitaional sag of the chamber. For the in-plane
alignment system, two camera's and four masks are mounted on the RO and HV crossplate respectively and the central crossplate houses four lenses. With two
parallel and two diagonal light rays several deformations of the
spacer and thus chamber can be monitored; most notably the sag and 
torque of the chamber. The torque is a relative rotation of the two outer
cross-plates. A total of 10 temperature sensors are mounted on 
the crossplates to monitor temperature gradients.

Tubes of the same layer lie in  the
same plane. The tubes of an adjacent layer is shifted by 15~mm (the 
half of the tube's width) and stacked as illustrated in figure~\ref{stacking}.
Tubes of the same layer are grouped in series of three (tripplets) 
 to reduce the number of gas connections to the onchamber manifold.
 Only the first and last  tube in the tripplet connects to the manifold
 at the RO side and HV side respectively, while the tubes are connected
with plasticxxxxx gas jumpers as shown in figure~\ref{triplet}.
 During assembly the length differences of the tubes are absorbed by
using jumpers of appropriate thickness (in steps of 100\um, maximal 300\um).

The mounting of electronic boards, equipped with xxxxconnections, is 
carefully prepared by fixing the rotation of the tubes such that the
ground pins finally lie in line within 0.5~mm.  
In the next chapter we elaborate on the on-chamber services. 

Practically, the position requiment of 20\um on the wires 
 implies that  the drift tubes  should be accurately  assembled into a 
chamber near the endplugs at the outer cross-plates.
 The straihgtness of the tubes in between the endplug is of less importance.
Therefore, we aimed to set-up an assembly stand based on a granite table
 with precision mechanics, such as jigs to hold the drift tubes,
  machined with a precision of 10\um or better.
 During assembly, the position of the spacer and 
individual tubes near the outer cross-plates
need to be monitored to the same level. Below we describe the
 assembly station and the adopted procedure to routinely produce 100
BOL chambers at NIKHEF.



Figure~\ref{bolfoto} shows a final BOL chamber. Seen...............
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(5,0){\mbox{\psfig{file=fmmdtch1.epsi,height=8cm,angle=-90}}}
\end{picture}
\caption{\sl OVERNIEW: FOTO of a muon chamber. EVENTUEEL MET DETAILFOTOOS}
\label{bolfoto}
\end{figure}

%\subsection{Requirements}
%Before the gluo
%During assembly of the chamber, i.c. the gluing of tube layers, the
%  position of the spacer has to be monitored to ensure that possible deviations
%of the outer crossplate which determine the relative wire position
% remain below 10\um. 
%
% The position of the inner crossplate is less stringent and is
%
%
%Consider as an example, a horizontally mounted chamber. The gravitational sag
% can be as large as 2~mm. In this case the tubes sag by 2~mm,
% while the wires maintain their nominal gravitational sag of 406\um.
% As mentioned in Section~\ref{tubereq},
%the cocentricity of the wire should stay below 100\um RMS, which imposes
% us to equip each chamber with a system to adjust
% the sag of the whole chamber and thus the tubes to follow that of the wires 
%depending on its final orientation in the ATLAS experiment.
%

\subsection{Assembly station} 
The gluing of six layers of 72 tubes onto a structure with dimensions 
5m $\times$ 2m , with a precision of 20\um is a delicate procedure.
 Depending on the actual layer to be glued, mistakes are costly in time
 and material.
 We constructed an accurate assembly station and adopted a robust procedure
 to assemble the muon chambers with high precision.

FOTOOS
\begin{itemize}
\item chamber
\item table, jig , spheres, suction,
\item guido, rasnik,
\end{itemize}




\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
% \put(0,0){\mbox{\epsfysize=10cm\epsffile{Bol_room_febr2000.ps}}}
\put(0,0){\mbox{\epsfysize=10cm\epsffile{bolglulastlayer.ps}}}
\end{picture}
\end{center}
\caption{\sl
Picture taken in the cleanroom, illustrating the last step of the chamber assembly. The jigs on the granite table hold the final tube layer. The chamber, which
consistst at this point of the spacer with 3 layers on top and 2 layers at the bottom is lowered on the last tube layer. Also visible are the stacking towers,
 sag compensation towers and RASNIK towers that control the positioning of
the spacer. (xxxxxxxxxx indicate this in pixture? xxxxxxxx)}
\label{bolroom}
\end{figure}

Figure~\ref{bolroom} shows the granite table equipped with precision mechanics.
  The end-plugs are hold 
by the outer jigs, which  are constructed and positioned
 with a tolerance of 10\um.
The stacking towers have the same accuracy and have adaptable heights to absorb the thickness of the vertical pitch of the tube layers. 
The central stacking position is shifted by half the horizontal pitch as appropriate.
The jigs are fixed at the west side, the reference side,  and can expand freely to absorb  temperature variations. 
These components, combined with a stable and uniform temperature  (typical variation $<0.5^{\circ}$C over one day) allow to assemble chambers within the 20\um RMS precision requirement.

During assembly, extensions with precise spheres (diameter 6cmxxxx) are mounted on the cross-plates as can be seen in figure~\ref{bolroomtower}. 
The stacking towers at the reference side support the spheres with so-called sphere-holders that can move  freely in the $x$ direction to absorb temperature variations.
 At the  east side, the non-reference side, the sphere-holders can move freely in  the horizontal plane. 
The sphere-holders are designed such that their height during possible horizontal movements is maintained with an accuracy better than a few microns.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
% \put(0,0){\mbox{\epsfysize=10cm\epsffile{bolroom_1.ps}}}
\put(0,0){\mbox{\epsfysize=10cm\epsffile{rasas.ps}}}
\end{picture}
\end{center}
\caption{\sl The picture shows the stacking tower
supporting the extension of the spacer. The position of the spacer is
monitored the alignment system. xxxxxxxxxindicate in the piture?xxxxxxxx }
\label{bolroomtower}
\end{figure}

When the spacer (with or without already fixed tube layers) is supported by the stacking towers the gravitational of the cross plates is considerably, of the order of 50\um.
To reduce this sag considerably to typically 10\um the unfinished chamber is carried by an additional system.
One of the the eight pneumatic cylinders constituting this system is also visible in figure~\ref{bolroomtower}.


\subsection{Chamber assembly}
FOTOOS
\begin{itemize}
\item chamber
\item table, jig , spheres, suction,
\item guido, rasnik,
\end{itemize}

 The assembly procedure starts with the assembly of the bare spacer, with a 'loose' accuracy of typically 500\um. 
Then, the tubes are attached, layer by layer, using glue. The time for the
glue to cure sets the

As already mentioned the quality control during chamber assembly start with re-measuring the wire tension of the tubes to be glued in the particular sequence.
After this test, the tubes are positioned in the jigs and the horizontal  position of the end-plugs, both at the RO and HV side,  is measured using laser beam running parallel to the end-plugs~\cite{glaser}.
For this test, a reference rod is placed between two adjacent tubes which
partially blocks the laser beam measured by an optical sensor.
Deviations in the response respresent a measure of deviations in tube heigts.
Note that by measuring between adjacent tubes,
 the results of this test are somewhat ambiguous case
neighbouring tubes are both badly poistioned. In addition, the test 
is sensitive to tube heights ($y$) as well as to the distance ($z$)
between tube pairs and the radii of the corresponding end-plugs. 
On the other hand,  
a badly positioned tube shows up twice and is tagged easily.
In practice, only a few tubes 
needed to get re-positioned.
 In some rare cases, we had to replace the complete tube due to,
 as it turned out, bad swaging of the end-plug.
 Bad swaging occurred for a particular batch of tubes where the end-plug was not well inserted in the aluminium tube.
We aimed at tube height deviations below 20\um and investigated all tube pairs
with responses above 10\um were inspected by the operators.

The result of these measurements as shown in figure~\ref{resgu}, indicate that the tubes are well positioned.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=resgu.eps,height=10cm,angle=0}}}
\end{picture}
\caption{\sl Tube positions during assembly. }
\label{resgu}
\end{figure}

After position of the tubes glue (Araldytexxxxx) is dispensed by means of an automated gluing machine.
  For the first (and later second layer), glue is dispensed  only in between adjacent tubes.
 The relevant side of the cross-plates is supplied with a sufficient amount of glue (3Mxxxxxx) and the spacer is lowered onto the tube layer.
To check the correct positioning of the spacer  we used RASNIK systems that monitor the cross-plate extensions at the four stacking towers at the corners
of the assembly table.
 In addition, we used a temporary  RASNIK system on both the HV and RO crossplate to monitor their sag.
Together with the 'standard' in-plane alignment components of the spacer, these RASNIK systems provided crucial position information with an precision of 10\um, which may be regarded as remarkably accurate for such large structure.


PLOTRASNIK, Graziano


After glue curing for at least 12 hours the spacer with the first tube layer is rotated upside down, effectively over its $x$ axis, thus respecting the reference side. The second tube layer is prepared the similar procedure as
for the first layer is followed. Now both sides of the spacer have a tube
 layer attached to it.  To glue the third layer, the spacer is lifted
and the stacking tower height is adapted to attach the third tube layer.
 On the tubes of the third layer and onward, two additional glue ropes
 (Araldytexxxxx) are dispensed to connect adjacent tube layers.
To glue the fourth layer, the spacer with its three tube layers is 
rotated back to its original
 orientation, limiting the (un)balance of the spacer and tube layers
 and thus avoids possible effects of asymmetrical weight distribution.
 After gluing the fifth layer the chamber is turned once more to finish it by attaching the sixth layer.

About every 25-th chamber several  checks concerning the accurate positioning of the mechanics were performed.
 Notably, the distances  between the corner stacking towers and the corresponding jig at the RO and HV reference side was measured with an auxiliary device.
 When these distance deviate, the chamber obtains  an unwanted stereo angle build in. 
Our checks demonstrated that such stereo angle is smaller than 4 \urad over the full period of the production.





 
\subsubsection{Results of X-ray scans}
About 10\% of all chambers undergo a mechnical precision check in
 X-ray tomograph~\cite{tomo} at CERN. 
The tomograph consists of a unit with two stereo X-ray beams 
that runs over the chamber in the $z$ direction at a fixed $x$ position.
Scintillator counters measure the 'shadow-pattern' of the wires and tube-walls.
A dedicated analysis of such pattern results in a wire position map
with an accuracy of typical 5\um. The chamber is considered certified
as the distribution of the residuals with respect to the nominal wire map 
has an RMS below 20\um. Table~\ref{tabres} lists the RMS values of the
residual distribution for the scanned BOL chambers. The numbers indicate
that these chamber are assembled according to the specifications.
\begin{table}[htb]
\begin{center}
\begin{tabular}{||l|c|c|c||} \hline
      &   RMS z\um    &  RMS y\um & RMS combined \\
BOL 2 &  1000      & 0000 &    0 \\ \hline
BOL 3 &  1000     &  0000 &    0 \\ \hline
\end{tabular}
\caption{\sl The table list for each scanned BOL chamber the residuals of
the wire coordiantes obtained in the X-ray tomograph. 
The numbers of the BOL chambers refer to their serial production number.  }
\label{tabres}
\end{center}
\end{table}


 In figure.~\ref{ztomras} we compare the layer Z-pitch deviations
 obtained by the X-ray tomograph
 with those derived from the RASNIK monitoring at the time
 the layers were glued.
The RASNIK deviations are shifted to set their
 average deviation to zero as appropriate for this comparison.
The distribution of the differences of the two measurements has an RMS of 6\um, indicating
 that the quality control during the assembly is well understood.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfysize=12cm\epsffile{ztomras.ps}}}
\end{picture}
\end{center}
\caption{\sl   Comparison of results from the tomograph scans for chambers
BOL0, BOL2 and BOL3 with RASAS data taken during glueing of the layers
of these chambers. For each chamber a set of 4 plots show the
deviations from the nominal Z layer pitch for the 3 layers within
each multilayer ( MLI and MLII) at the HV and RO side respectively.
xxxxxxxxxxxxxxxxxxkeep it? Then, renew itxxxxxxxxxxxxxxxxx
}
\label{ztomras}
\end{figure}



\section{Chamber services}
\paragraph{Alignment components}
As mentioned before, physical deformations of the chambers are monitored
 with the in-plane alignment system consisting of four RASNIK systems 
mounted during chamber construction.
The inter-chamber alignment consist of RASNIK systems monitoring the position of neighbouring chambers of the same type and RASNIK systems that monitor the
 projective alignment of the three muon chamber layers.
 In a test setup at CERN~\cite{DATCHA} it was demonstrated that an alignment
 accuracy better than 10\um (on the change of the relative chamber positions) can be achieved with this system. After chamber construction the mounting platform for these system are glued on the chambers.
The components for the in-plane RASNIK systems are shown in figure~\ref{rascomp}.
 The power and readout for all
alignments systems is provided by an on-chamber multiplexer, called
RASMUX, which itself is later connected through one D-25 cable 
to a master system that steers 
and collects information of several muon chambers. The RASMUX is also shown
in figure~\ref{rascomp}.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfxsize=14cm\epsffile{rascomp.ps}}}
\end{picture}
\end{center}
\caption{\sl   
Picture of several alignment components.
}
\label{gassystem}
\end{figure}


\paragraph{Temeprature and magnetic field sensors}
 A total of 16 temperature sensors provide supplementary information on
 possible chamber deformations. In addition, typical a few magnetic field
sensors probe the field for off-line corrections. These sensors
connect to the detector control system. The DCS is configured and readout with
the CAN protocol.


\paragraph{Gas system}
After the mechnical completion of the chambers, we started with
installing the gas system.
The on-chamber gas system consists of two gas manifolds for each multilayer.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfxsize=14cm\epsffile{gashvmask.ps}}}
\end{picture}
\end{center}
\caption{\sl   
Picture taken the HV side of a BOL chamber. 
Some individual tubes can be recognized together with the connections to
 the gasmanifolds. Also shown is a HV board and the backplate of the RASNIK mask
component.
}
\label{gassystem}
\end{figure}
Tubes of the same layer are grouped in series of three (tripplets) 
 to reduce the number
of gas connections to the manifold. Only the first and last
 tube in the tripplet connects to the manifold at the RO side and HV side
 respectively. 
After installing the 
gas system, the chamber is filled to 3~bar and its pressure 
(corrected for temprature effects) is monitored for at least 24 hours
to assure the gas tightness of the added components. The manifolds have only 
one input or output and can be quickly connected to the gas service in the
experiment.


\paragraph{Electronics}
All the tubes in the chamber are provided with a ground pin at the RO and HV
side respectively. The ends of the ground pins and the pins on the gas caps
all lie in the same plane as can be seen in figure~\ref{gashvmask}.
The  and HV electronic boards  are provided with xxxxxxxxxxconnetor
to connect to the pins robustly. The digital signal processing and the final
time measurement is embedded on so called 'mezzanine' cards that directly connect
to the analogue RO electronics and are housed in individual faraday cages.
The digitized signals are shipped to a central on chamber processor card (CSM)
as shown in figure~\ref{roend}. 
The CSM is configured via the DCS and  connects to the experiment data acquisistion 
system by optical fibers.


\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfxsize=14cm\epsffile{roend.ps}}}
\end{picture}
\end{center}
\caption{\sl   
Picture taken at the RO side of a nearly completed BOL chamber. 
The RO electronics of the top and bottom multilayer is enclosed in Faraday cages.
Also visible are the backplates of the RASNIK cameras, the DCS control box for
 the temperature and B field sensors, the readout motherboard 
 and two RASMUXes as required for this specific chamber.
 }
\label{roend}
\end{figure}





\section{Broken wires}
WHERE???????????????????????????
After the completion of the first chambers we detected a number of broken
wires in several chambers. Despite many dedicated studies, 
the cause of this problem has not been recovered. However, we observed that
broken wires seem to occur only  in chambers that
have 'seen' high gas flows (xxxbar/l).  Moreover, this problem is
 restricted  
to the first (or last) tube of a triplet connecting to the gas manifold.
To avoid such high  flows we put mechnical flow restrictors in the on
 chamber gas outlet tubing. In total we have xxxx chambers with broken
wires. Usually, the number of broken wires is limited to 1xxxxx,
except for one chamber, BOLxxxx, whch has the 24xxxx broken wires.
We repair the broken wires, using a procedure that uses the existing
o-ring and thus not requires any glue.
 This comes not for free. The accuracy of the 
wire position is estimated to a few 100\um. In principle, the wire position of
 such wires can be obtained later in the ATLAS experiment with a
 procedure that uses tracks xxxxxxxxxxxxxxxxmore?.



\section{Tests of completed chambers}
The main purpose of the test stand is to verify the electronic read-out
 of each chamber under ATLAS gas (Ar/CO$_2$= 93\%/7\% at 3~bar) and HV (3300V)
 conditions. 

\subsection{Cosmic ray test stand}
The cosmic ray test facility at NIKHEF 
 accomodates five BOL chambers and has a fixed trigger system as shown
in figure~\ref{cosray}. The trigger units (also visible in the figure) 
consist of two layers of scintillators, separated by
50cm thick iron block to filter out the low energetic muons
 (i.c. muon with energies smaller below 0.7~GeV). 
Since the summer of 2004 till the autum of 2005 we routinely
tested BOL chambers; usually we exhanged three chamber middle chamber and
kept the outer chamber in place to have a stable reference.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=10cm \epsffile{cosmicstand.ps}}
\caption{\sl
Picture of the cosmic ray stand with five BOL chambers. The chamber in the
in the highest position is a small type BOL chamber with a width of 48 tubes.
}
\label{cosray}
\end{center}
\end{figure}


\subsection{Results}
 Figure~\ref{drifttime} show a typical difttime distribution
for a single wire.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{xxxx.ps}}
\caption{\sl
Drift time distribution xxxxxxxxxxxxget it, if we want itxxxxxxxxxxxxxxxx
}
\label{drifttime}
\end{center}
\end{figure}
 The $t_0$ and $t_{max}$ for each individual wire
is extracted from its drifttime distributions. Large deviations are a good
indicator for problems. We often observed a pattern related to groups of 
three drift tubes constituting a gas-tripplet. After an extended period
of flushing (xxxxxxx liter) these structures disappear.
 One, and only one, severe problem remains, which  are
the broken wires observed in some chambers as mentioned above. xxxxxxxxxx

Further analysis of the data uses software being developped for ATLAS and
involves  driftdistance versus drifttime  calibration with 
corresponding track fits to drift circles in individual chambers.
The distribution of the residuals for a representative wire is shown
 in figure~\ref{residual}.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{xxxx.ps}}
\caption{\sl
Residual. xxxxxxxxxxxxget plot if we want it.xxxxxxxxxxxxxxx
}
\label{residual}
\end{center}
\end{figure}
The efficiency for single hits is 9xxxx\% and the resolution
is xxxxxx\um as expected for the current conditions. 


ONDERWERPEN/FIGUREN:
\begin{itemize}
\item hit distributions
\item drift properties: TMAX
\item efficiencies
\item tracks
\item problems
\item wire/layer locations (correlations XTOMO)
\end{itemize}
 

%We attempted to reconstruct the (relative) wire positions
%in some individual chambers. But as
%could be expected, the correlations between the positions and
%the essentially vertical direction of the muons limits the
%sensitivity to an estimated 100\um. No inconsistentices have been observed.
%In addition, we used tracks 
%to extract the relative position and orientation of individual chambers. 


\section{Chamber transport to CERN and instalation in ATLAS}
ONDERWERPEN:

handling tools, common supports, RCP assembly


Figures:
\begin{itemize}
\item Trasnport frames
\item Work at CERN: common support
\item BOL above magnet (photo exists already)
\item installed BOLs
\end{itemize}

 

\section{Conclusions}
chambers are within specs.

\clearpage

\begin{thebibliography}{99}
\bibitem{tdr}
The ATLAS MUON TDR, 
http://atlasinfo.cern.ch/Atlas/GROUPS/MUON/TDR/Web/TDR.html

\bibitem{DATCHA}
 First System Performance Experience with the ATLAS High Precision
      Muon Drift Tube Chambers
      Poster presented by  M. Vreeswijk at Vienna WCC 1998.
      Published in Nucl.Instrum.Meth.A419:336-341,1998 \\
http:\/\/atlasinfo.cern.ch\/Atlas\/GROUPS\/MUON\/datcha\/datcha.html

\bibitem{woudstra}
M. Woudstra, PhD Thesis, to be published
\bibitem{kloe}
 ELECTROSTATIC DIGITAL METHOD OF WIRE TENSION MEASUREMENT FOR KLOE DRIFT CHAMBER.
A. Andryakov et al.. 1998.
Prepared for 7th Pisa Meeting on Advanced Detectors:
 Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba, Italy, 25-31 May 1997.
Published in Nucl.Instrum.Meth.A409:63-64,1998 \\
MDT wire tension measurement using an electrostatic method,
 ATLAS internal note, ATL-MUON-38-264. 

\bibitem{emmi}
 An electromagnetic micrometer to measure wire location inside an
ATLAS MDT drift tube, Cambiaghi, M., Cardini, A., Ferrari, R., Gaudio,
G., ATLAS Internal Note ATL-MUON-1998-259, 1998 


. M. Cambiaghi et al., Proceedings of the 1999 IEEE Nuclear Science Symposium, IEEE Trans. Nucl. Sci. 47 (3) 2000. 



\bibitem{glaser}
ATLAS Internal Note MUON-NO-
29 September 1998 
A QA/QC system to monitor the planarity of the tube layers in MDT chambers
 construction
G. Ciapetti, G. De Zorzi, R. Giacalone, L. Montani, D. Pinci
Dipartimento di Fisica, Università di Roma "La Sapienza"
and
INFN, Sezione di Roma


\bibitem{spare}
%\cite{Bini:2001qf}
\bibitem{Bini:2001qf}
C.~Bini {\it et al.},
%``The Pavia-Roma1 ATLAS MDT Quality Control System,''
Nucl.\ Instrum.\ Meth.\ A {\bf 461} (2001) 65.
%%CITATION = NUIMA,A461,65;%%


 
\end{thebibliography}


\appendix

\section{Alignment system RASNIK}
\label{app:rasnik}
RASNIK is the acronym for Red ALignment System NIK(HEF). 
The 'red' refers to the color of the LEDs  used in the very first version
 invented at NIKHEF.
The system consists of a coded mask that is (partially)  projected
by a lense on a camera as shown in figure~\ref{rasnikprinciple}.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfysize=6cm\epsffile{rasnikprinciple.ps}}}
\end{picture}
\end{center}
\caption{\sl 
The principle of RASNIK.
}
\label{rasnikprinciple}
\end{figure}
 The basic binary blocks have
dimenesions  of 100\um $\times$ 100\um and form a chessboard like pattern
as can be seen in figure~\ref{mask}. 
An additional code on each nineth row and column, also visible in the figure,
allows to reconstruct the coarse alignment. 
This set-up measures relative transverse movements (X,Y)
with respect to the optical axis, the relative rotation ($\alpha$) over the optical axis  of the mask and the camera and the ratio of the distance of the 
lense-camera and lense-mask (the $scale$).
The resolution depends on several parameters, such as the quality of
the lense. Especially for large distances between mask and camera,
temperature gradients in the air affect the light path deteriorating the
resolution. However, for a setup of
 1~m long (in total), a precision of 1~\um on transverse movement,
 50\urad on the rotation and $10^{-4}$ on the scale is achieved. 
is measured with a resolution of 50\urad and the 
scale to $10^-4$. 
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfysize=12cm\epsffile{rasnikmask.ps}}}
\end{picture}
\end{center}
\caption{\sl 
The coded mask.
}
\label{mask}
\end{figure}


The alignment of the ATLAS muon system is completely based on the RASNIK
principle as can be read in detail in~\ref{atlasalign}. 


\end{document}



