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\title{ATLAS muon chamber construction at NIKHEF}
\author{NIKHEF ATLAS MUON GROUP \\ 
Contact: Marcel Vreeswijk, h73@nikhef.nl} 
\date{November 2005}


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\maketitle



\begin{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{abstract}


\newpage

\tableofcontents

\listoffigures

\newpage

\pagestyle{plain}
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\section{Introduction}
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfysize=14cm\epsffile{adet.ps}}}
\end{picture}
\end{center}
\caption{\sl   
Picture taken in the fall of 2005 of the ATLAS detector under construction.
The coils for the toroidal magnetic field can be recognized togheter with their support structures that also carries the muon system. On the bottom-right 
part of the picture, 
 a drawing of a cross sectional view of the muon spectrometer is displayed,
together with the feet that carry the ATLAS detector.
  This gives an impression of the location and size of the three layers
of muon stations. 
The largest type of the outer layer, the BOL chamber is indicated.
 In the longitudinal direction (pointing in the paper)
12 muon chambers are positioned of each type.
 In the center of the picture, the calorimeter (not yet at its final
position) is visible.  
}
\label{atlasdet}
\end{figure}
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(0,0){\mbox{\epsfysize=14cm\epsffile{../auke/mv_measprinciple.ps}}}
\end{picture}
\end{center}
\caption{\sl   
Illustration of the MDT measurment principle. The figure shows two muons 
entering a drift tube. One of the muons (the one in the back) passes relatively close to the wire and thus has small drift distance as indicated by the circle with corresponding radius. The other muon passes wire at a large distance as indicated.
}
\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{atlasdet}. 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{mdtprinciple}. 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=../auke/mv_inplane.ps,height=8cm,angle=0}}}
\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}
For later use we define the coordinate systems.
 When the chamber is located on the assembly station 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.


\clearpage


\section{Drift tubes}
A schematic view of a drift tube is shown in figure~\ref{tube}.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=14cm \epsffile{../auke/mv_endplugtwister.ps}}
\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.ps}}
\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????


\clearpage

\subsection{Drift tube requirements}
\label{tubereq}
The meet the precision requirement on the total chamber, the 
contribution of individual drift tubes has to remain well below 20~\um to 
accomodate the finite accuray of the tube positioning during chamber assembly.
 
This imposes the accurate machining of the end-plugs and wire locators,
which determine the position of the wire near the tube ends. We required
the precision rings be machined within 10~\um with respect
to the axis of the endplugs.

Near the middle of the tube, away from the endplugs, the wire tension
determines the position of the wire (with respect to the precision ring).
The wires of the BOL chambers are tensioned at 285~gram, which corresponds to a maximal gravitational sag of 406\um. To limit the uncertainty (RMS) on this
value to 10\um precision an accuracy of 7~gram is required on the wire
tension.

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 south side (as we define it),  several components are indicated.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=8cm \epsffile{wmach.ps}}
\caption{\sl
Picture of the wire machine taken at the south side. On the left the empty tubes come in. The tube in the center is being wired and will roll off at the right, where futher quality checkes are performed.
}
\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.
 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~Hz corresponds to 285~gram.
 The results of the second tension measurmeent are shown in
 figure~\ref{fig:tens}. The precision of the wire tension over the full period of time is 0.33~Hz, which correcponds to about 6~gram (or 8~\um maximal sag).
We decided to reject tubes with deviations larger than 1.5~Hz away from the
nominal value, which led to the rejection of 21 tubes. 

 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{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.


\clearpage

\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.

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 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. A schematic view of the sag adjustment system is shown in figure~\ref{sagadjust}.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfxsize=14cm\epsffile{../auke/mv_sas_greyscale1.ps}}}
\end{picture}
\caption{\sl Schematic view of the sagadjustment system in the middle crossplate. Shown is the longbeam that is connected to this crossplate with a SPINDEL. By simply turning the SPINDEL the heigth of the middel cross plate 
with respect to the longbeam and is adjusted, enabling to align the middle crossplate with respect to the outer crossplates. }
\label{sagadjust}
\end{figure}

 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}.
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\psfig{file=../auke/mv_stacking.ps,height=5cm,angle=0}}}
\end{picture}
\caption{\sl Schematic view of a chamber with several tubes left out to illustrate the stacking of tubes into layers.  }
\label{stacking}
\end{figure}

Tubes of the same layer are grouped in series of three (tripplets) 
 to reduce the number of gas connections to the on-chamber 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. 
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. 


%\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.
%

\clearpage

\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.
A picture of a   mecanically completed BOL chamber on the assembly station 
is shown in figure~\ref{bolfoto}. Below, we describe in detail the 
setup and the assembly steps. 
\begin{figure}[htb]
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfxsize=12cm\epsffile{bol0af.ps}}}
\end{picture}
\caption{\sl finished BOL}
\label{bolfoto}
\end{figure}


\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfysize=10cm\epsffile{station.ps}}}
%\put(0,0){\mbox{\epsfysize=10cm\epsffile{bolglulastlayer.ps}}}
\end{picture}
\end{center}
\caption{\sl
Picture taken in the cleanroom showing the assembly table. Several key items are indicated. }
\label{bolroom}
\end{figure}
Figure~\ref{bolroom} shows the granite table equipped with precision mechanics.
The cartesian coordinate system and the north (N), south (S) and west (W)
 sides are also indicated.
All jigs are equipped with vacuum suckers to
hold the tubes firmly positioned.  The end-plugs are hold 
by the outer jigs, which  are constructed and positioned
 with a tolerance of 10\um. 
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}a.
These extension house a RASNIK-mask, monitored by the so called RASNIK monitoring system as indicated in the figure.
Using exchangable  blocks (also indicated in the figure),
 the stacking towers 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 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{\epsfxsize=8cm\epsffile{tower.ps}}}
\put(7,0){\mbox{\epsfxsize=8cm\epsffile{sagcomp.ps}}}
\end{picture}
\end{center}
\caption{\sl a) The picture shows the stacking tower
supporting the sphere in the extension of the spacer.
 The position of the extension is
monitored by a RASNIK alignment system. 
b) This pictures shows the stacking tower together with the
sag compensation tower.}
\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}b.

After the construction of 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.




\subsection{Chamber assembly}
 The assembly procedure starts outside the cleanroom  
with the construction of the bare spacer, 
with a 'loose' accuracy of typically 500\um. 
Then, in the cleanroom, the tubes are attached layer by layer using glue.
 This process typically takes half a working day,
 but the time needed for the glue to cure,
 constraints the production-speed to one layer a day.

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 gas jumpers
are temporary fixed  in a way such that tube length differences within
 a triplet are absorbed as illustrated in in figure~\ref{triplet}, which
ensures a tight connection of the jumpers on the tube. 
Additionally, to position the end-caps of an entire 
tube layer in-line,   we use jumpers  of appropriate thickness 
(in steps of 100\um, maximal 300\um), which later on facilitates the
the mounting of electronic boards.
\begin{figure}[htb]
\begin{center}
\mbox{\psfig{file=../auke/mv_triplet.ps,height=10cm,angle=-90}}
\end{center}
\caption{\sl Illustration of gastriplets.}
\label{triplet}
\end{figure}

After this procedure, the jumpers are loosened to avoid unwanted stress
between neighboring tubes that could prevent the tubes to fall into their
jig position. Then,  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} as indicted in figure~\ref{bolroom}.
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 in 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 as shown in picture~\ref{build}a.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,10)
\put(0,0){\mbox{\epsfxsize=7cm\epsffile{glumach.ps}}}
\put(8,0){\mbox{\epsfxsize=7cm\epsffile{bolinkraan.ps}}}
\end{picture}
\end{center}
\caption{\sl a) Glue dispension by the gluing machine. 
b) attaching another layer.}
\label{build}
\end{figure}

  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.
The correct positioning of the spacer is checked using the 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, one multilayer with three tube layers is finished.Figure~\ref{glueropes} shows the distribution of glues between the tubes in a
finished multilayer.
\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(12,5)
\put(0,0){\mbox{\epsfxsize=5cm\epsffile{../auke/mv_tubegluing.ps}}}
\end{picture}
\end{center}
\caption{\sl   
Illustration of the distribution of glue between the tubes in a multilayer.
}
\label{glueropes}
\end{figure}
The chamber is turned once more to finish it by attaching the sixth layer.  A picture of the final chamber still on the granite table was already shown in figure{bolaf}. 




 
\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}


\clearpage

\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 
this system achieves an alignment
 accuracy better than 10\um (on the change of the relative chamber positions).
 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{rascomp}
\end{figure}


\paragraph{Temeprature and magnetic field sensors}
 A total of 18 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 (DCS). 
The DCS is configured and readout with the CAN protocol.


\paragraph{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{gashvmask}
\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 temperature 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 xxxxxxxxxxxxxxxx
}
\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. 

\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{eff.ps}}
\caption{\sl
Efficiency for BOL002 as a function 
of the tube number.
}
\label{eff}
\end{center}
\end{figure}


\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{hits.ps}}
\caption{\sl
Hit distribution for BOL002 as a function 
of the tube number.
}
\label{hits}
\end{center}
\end{figure}


\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{resol.ps}}
\caption{\sl
Resolution for BOL002 as a function 
of the tube number.
}
\label{resol}
\end{center}
\end{figure}



\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{t0tmax.ps}}
\caption{\sl
The $t_0$ and $t_{max}$ distributions for BOL002 as a function 
of the tube number.
}
\label{t0tmax}
\end{center}
\end{figure}



\begin{figure}[htb]
\begin{center}
\mbox{\epsfxsize=6cm \epsffile{zposition.ps}}
\caption{\sl
Wire position deviation in the $z$ direction for BOL002 as a function 
of the tube number.
}
\label{zposition}
\end{center}
\end{figure}


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 

\bibitem{tomo}
tomograph


. 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{pavia}
%\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;%%



\bibitem{rasnikpaper} The RASNIK alignment system. To be published in Nucl. Instr. and Meth.
 
\end{thebibliography}


\appendix

\section{Alignment system RASNIK}
\label{app:rasnik}
The Red Alignment System NIKhef (RASNIK) consists of a coded mask, a lens
and a video image sensor~\cite{rasnikpaper}. The mask, illuminated with (infra-red)
LEDs from behind,
is projected by the lens onto the image sensor as illustrated in figure~\ref{rasnikprinciple}.
\begin{figure}[htb]
\begin{center}
\mbox{\epsfysize=5cm\epsffile{rasnikprincipleshort.ps}}
\end{center}
\caption{\sl 
The principle of RASNIK.
}
\label{rasnikprinciple}
\end{figure}
 A daylight-blocking filter
is placed before the
image sensor.
If the lens is displaced in the direction perpendicular to the optical axis,
then the image on the sensor will be displaced in the same direction,
magnified with a factor $(v+b)/v$,
where $v$ is the object distance and b the image distance.
If the lens is displaced along the axis, the image scale $S$ will change following $S = b/v$.
Finally, if the mask rotates around the optical axis with respect to the sensor,
the image rotates accordingly. From the analysis of a RASNIK image, four parameters
can be deduced: two tranversal displacements, one displacement along
the optical axis, and the relative rotation between the mask and sensor
around the optical axis. The changes are relative: a common shift of three
components does not change the readout values. The changes can be expressed,
for instance, in terms of a mask displacent or a lens displacement.

A typical RASNIK image is shown in figure~\ref{ima}, clearly displaying the chessboard pattern,
in which each 9th row and 9th column is carrying a digital code.
This code has the values (0,0) in the bottom left of the masks,
and increases linearely with the coded column and
row numbers into the direction of the top-right corner in the mask.
In this way the coarse position of the image, showing only a small part of a large mask,
can be identified.

The video signal of the sensor is digitised by means of a frame grabber in a pc.
After differentiating the image data, the contours of the chess fields appear as
an orthonormal grid pattern. From this, the 'fine' image position, image scale
and image rotation are obtained.
After detecting and decoding the 9th row and columns, the coarse image position
is obtained.

Due to the large summed length of chess field contour on an image (~ 100 mm,
in both directions),
a precision of 50 nm (RMS) is obtained in the two transversal directions in terms
of image position on the sensor, per image. The image scale is measured
with a resolution better than $5 \times 10^{-5}$ (RMS), and the resolution of the
image rotation is 20~\urad (RMS). When placed in air, the RASNIK performance is
limited by the gradients and fluctuations in the gradient of the air temperature.
The linearity of the system is exclusively determined by the precision of the mask.
For ATLAS, we applied low- cost 'contact copies' of mother-masks made in VRSI industry,
and their precision was guarantied to be better than 0.1~\um.
The range of a RASNIK system is determined only by the mask size, and can be
as large as 125 $\times$ 125 mm$^2$. For the InPlane systems we applied mask segments of 20 $\times$ 20 mm$^2$,
and for the projective systems masks of 50 $\times$ 50 mm$^2$ were used.

A RASNIK system can be calibrated by placing the three components in a well known
relative position, while recording the readout values. After that, the deviation from
the initial alignment can be obtained from the difference between the actual readout
values and the calibration values.

\begin{figure}[htb]
\begin{center}
\setlength{\unitlength}{1cm}
\mbox{\epsfxsize=8cm \epsffile{ima.ps}}
\end{center}
\caption{\sl 
Typical RASNIK image with the chess sboard pattern and the coded row
and columns. The light intensity of the pixels under the indicated line
is plotted, together with its derivative.  The Gaussian peaks
(positive and negative) determine the fine position of the image, as well as
the image scale.
}
\label{ima}
\end{figure}






\end{document}



