THE ATLAS Muon Drift Tube assembly site in
University of Athens
D. Fassouliotis, P. Ioannou and C. Kourkoumelis
University of Athens
Annual conference of the Greek Society for the Study of HEP
Ioannina,April 2000
Abstract
This talk describes the University of Athens Muon Drift Tube assembly line.
The nessecary tooling together with the procedure followed for the wiring is
presented. Experience and results of the performance are described based on the
assembly of 295 tubes used for the BIS module 0 prototype.
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Introduction
Three Greek institutions, the University of Athens, the National Technical
University of Athens and the Aristotle University of Thessaloniki have joinly
undertaken the responsibility of building part of the Muon Spectrometer for the
ATLAS experiment to operate in the new LHC accelerator,under construction at
CERN. More precisely,we are constructing the 128 muon chambers of the B(arrel) I
(nner) muon S(pectrometer).The muon chambers consist of M(onitored) Drift Tubes
(MDT’s),which are cylindrical drift tubes of finished length of 1671.5 mm and 30mm
diameter.The assembly of the 30,000 BIS MDT tubes is the responsibity of the
University of Athens. For this purpose we have set up a dedicated wiring line which
will be described below.
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General description of wiring site
The wiring procedure
In our wiring facility (1) we thread the 50 μm gold-plated wire through the
aluminum tube, place and crimp the end-plugs and crimp the wire after tensioning it.
This operation involves a number of precision steps since a) the wire must be
positioned with a 25 μm accuracy and be tensioned at (35017) gr, b) the tube has to
be assembled in such a way that the accuracy on the finished length is better than 250
μm and c) when operated at a pressure of 3 bar and a voltage of 3.4 kV, should have a
dark current below 3.5 nA and gas leak rate below 1x10-8 bar l/s.
The wiring table
The wiring table is placed in a dust free enviroment held at constant
temperature .It is an aluminum bench 50cm wide and 2.5m long (photo 1) on which
the various tools for wiring are installed. There are two basic tube stations/positions
used to accomplish the wiring and two additional positions for the QC checks plus
one fallback position, set up. Each position/station is used to accomplish a number of
different functions:
 Station 1:
The wire is threaded through the tube by a vacuum force and
through the end-plugs using compressed air. The wire is then crimped on one side
of the tube. The station houses the tube clamps, plus the wire spool and two wire
threading devices.
 Station 2:
The tube is crimped pneumatically on both sides. The wire is
tensioned by an automatic device and finally it is crimped on the other side of the
tube. The station houses the two gas crimpers and two tube clamps plus the
automatic tensioning devices.
 Station 3 (QC): Measurement of angle difference between the end-plug axis
and tube axis is performed.
 Station 4 (QC): Measurement of finished tube length is performed.
 Station 5 (presently not used, fallback solution): The wire can be tensioned using
weights. The station houses two tube clamps plus a frictionless pulley.
The tools used for wiring
Tube clamp: A simple mechanical clamp . The tube is clamped at a width of about
1 cm.
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Wire spooling and wire insertion: The plastic wire holder is mounted on a rotating
pulley. The wire is threaded through the tube by a vacuum force (photo 2). The wire is
attached to a frictionless light cylinder which is inserted into the tube. At the other
end a rubber cup is attached to a vacuum hose placed over the open end of the tube.
The vacuum pump is then switched on and the wire is pulled through the tube with a
speed of about 0.4m/sec.
Wire crimper: This is a simple “crocodile” spring plier At a later stage the spring
was replaced by a pneumatic cylinder.There are two such devices installed at each end
of the table.
Wire insertion devices: The endplug is positioned in a V-support (photo 3) and
pushed by hand against the air insertion device while, by means of a foot valve,
compressed air of about 2 atms from a gas bottle -in order to be oil free- is turned on.
There are two such devices installed at each end of the table.
Gas crimpers: They are built by Protvino ( photo 4 and 5). They perform four
different operations:
a) Crimp the tube pneumatically into the end-plugs using 200 bars of pressure.
b) Provide the clocking of the tubes (using guide pins which are
inserted into the end-plug threaded holes). The guide pins of both sides are
aligned during the alignment phase .
c) Provide the variable spacing between the end-plug and the tube end (both
sides) in order that the finished tube has at most a 100 μm fluctuation with
respect to the nominal length .
d) Determine the finished tube length as the fixed distance between the inner
back planes of the crimpers.
Wire tensioning system: It uses commercially available components: a three wheel
tension meter and a linear actuator pulling the wire (photo 6). A conventional PC
controls the tensioning process though a DAQ1 card using the LabView software.
Tube ruler: It consists of a precision aluminum through fixed on the table. A spring
mounted on the device is directly connected to a micrometer (10μm accuracy). The
contact of the spring with the end-plug is done by means of a hollow aluminum tube,
one end of which is in contact with the end-plug’s back surface and the other with the
spring2.
QA/QC procedure
After the completion of the tube wiring, two QC checks are performed on the
wiring bench:
 Measurement of the finished tube length.
This is performed by placing the tube in the tube ruler.
 Measurement of the coaxiality between end-plug axis and the tube axis.
The tube is supported by means of two jiigs, each made with two spheres
glued on the table. Each jiig supports the tube at the precision surface of the
end-plugs. The eccentricity is measured by means of a micrometer located 21
mm away from one of the spherical supports (photo 7). We measure the
1
2
National Instruments Co, PCI-MIO-16E-4
One measures differences only between the finished tube and a reference tube .
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difference in μm when the tube is rotated. This displacement is then converted
into angular difference.
Local Database
During the wiring and QC tests, all relevant data are entered in the local DDB.
All of them are inserted automatically using the LabView software. For the storage of
the information, we used the official Atlas MDT DB
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Results from Module 0
During June 1999, 295 tubes were wired for the BIS module 0 prototype,
following the procedure described above, without facing major production
difficulties. We achieved a goal of about 7.5 min/tube wiring time, of which about 11.5min/tube was devoted to the QC checks described above.
In figure 1 the number of wired tubes per production day is presented. Note
that the lower production rate during certain days, was mainly due to shortage of endplugs.
Both the length of the raw tube and the finished one were monitored. The
finished tube length, which has measured and registered for all tubes, is shown in
figure 2. The mean value of the distribution is, as expected, 1671.5 mm, while the
sigma is well below the precision requirement and found to be 50 μm. The raw tube
length, which actually reflects the tube fabrication precision is shown in figure 3.
The angle difference measurement for both end-plugs is shown in figure 4.On
one hand, our measurement of eccentricity provides an upper limit on the difference
of the coaxiality between end-plug and tube axis. On the other hand, our measurement
is the one that counts for estimating the interference between tubes on the jiig,when
tubes get prepared to be glued into chambers. Here one should note that out of the 295
tubes wired for module 0, only 1% had an angle difference between 2-3mrad.
However, no interference of tubes was observed during assembly at the Univ. of
Thessaloniki.
4 Conclusions
Using the wiring line described above we wired all the tubes of module 0
without facing any major problems. We used automatic feeding of the wire by a
vacuum force, high pressure gas for the tube crimping and an automatic wire
tensioning device. We implemented two additional QA tests on the wiring table.
Namely, the measurement of the finished tube length and a measurement of the
coaxiality between the tube and the end-plug axis. The net wiring time per tube,
including the QA tests was below 8 minutes. On May 1999,we were the first of the 12
construction sites who successfully passed the site review ,performed by a special
ATLAS committee,and the site was certified.
The standard QA/QC tests were performed in the NTUA and results are
presented elsewhere. The tubes were assembled at the Univ. of Thessaloniki during
July 1999. No mechanical problems related to construction accuracy, namely
interference in the jiigs were reported.
During winter 1999 ,as soon as improved end-plugs became available,we
continued the production, starting with module 1 . Few improvements were
implemented, but basically the production line is continously operating.Up to now
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(January 2001) we have produced more than 3,500 tubes (more than 10% of the full
production).
References
(1)
ATL-MUON-2000-014
Photo1: Side view of the wiring table. The storage racks inside the clean room can be seen in the
background.
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Photo 2: Wire insertion in the tube using the vacuum pump.
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Photo 3: Wire air insertion device (interior view).
Photo 4: the moveable crimper.
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Photo 5: View of the other crimper (on the right). Two of the tube clamps can be seen on the left.
Photo 6: View of the automatic wire tensioning system. Tension measurement device (foreground
left). Step motor (foreground right). Tension display unit (background left). Step motor control unit
(background right).
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Photo7: Tooling for measuring the tube end-plug axis angle difference.
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Figure 1: Distribution of the number of wired tubes per production day.
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Figure 2: Distribution of finished tube length.
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Figure 3: Distribution of raw tube length (Sub-sample of the wired tubes).
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Figure 4: Distribution of the angle difference measurement between the tube and end-plug axis. Both
end-plug sides were measured and are presented.
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