ATLAS Transition Radiation Tracker

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ATLAS Transition Radiation Tracker

• End-cap Quality Control
• and the Characterization of
• Straw Deformations

Michael Kagan University of Michigan Supervisor
Mar Capeans CERN REU 2004
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Outline

• ATLAS and the Transition Radiation Tracker (TRT)
• Quality Control and Commissioning End-Cap
  Acceptance Tests
• Straw Eccentricity and Ellipticity Distortions
• Conclusions
• Acknowledgements

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ATLAS Inner Detector
Inner Detector pixel, silicon and straw
tubes Combination of Central Tracker and TR for
electron identification
ATLAS Experiment
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The TRT Detector
Detecting element Straw Tube 4 mm O.D. 30 mm W/Au
wire
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TRT Barrel End-cap
Detecting element straw tube 4 mm diam., 30 mm
W/Au wire Robust operation conditions safe and
fast gas Xe/CO2/O2 (70/27/3)
End-cap
Layers of straws radiators
End-cap
HV signal readout
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Transition Radiation
Transition radiation is produced when a charged
ultra-relativistic particle crosses the interface
between different media, PP (fibres or foils)
air for the TRT. TR photons are emitted at very
small angle with respect to the parent-particle
trajectory.
Energy deposition in the TRT is the sum of
ionization losses of charged particles (2 keV)
and the larger deposition due to TR photon
absorption (gt 5 keV)
TR threshold electron/pion separation
5.5 keV
0.2 keV
e-
e-
MIP threshold precise tracking/drift time
determination
Radiator Foil
Straw tube
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End-cap production QC steps
Straw installation Gas leak tightness
Wiring
Wheel transfer
Wire crimping Wire tension HV
Wheel sealing Gas leak tightness HV
Wheel Test Wire eccentricity
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End-Cap Acceptance Tests

• At assembly sites and after reception at CERN
• Gas tightness
• HV
• Wire Tension
• Wire eccentricity

• Wheel Test Station
• Precise measurement of gas gain (1 accuracy) to
  derive eccentricity value per straw
• 6 points of measurements along each straw
• Slow control ( T, P, H, HV)
• Monitoring straws (6 points of monitoring)
• Electronics calibration
• Online/Offline analysis
• 4-plane wheel (3000 ch) characterization takes
  13 h

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Geometric Deformations
The straw tube signal amplitude spectrum from a
point ionization depends on the wire offset with
respect to the straw center (eccentricity) and on
the straw wall shape deformation (ellipticity).
Field lines in a straw tube with no wire offset
Field lines in a straw tube with 500 µm offset
Field lines in an elliptically deformed straw tube
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Experimental Setup
Precision magnetic support arms and a clock gauge
were used to bend and squeeze the straw with a 10
micron accuracy.
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Eccentricity Results
For straw eccentricities greater than 400
microns, the straw operation is observed to be
unstable. However, we can not directly measure
the wire offset. Thus, one must use measurable
parameters in order to examine the quality of a
straw, such as the signal amplitude and the straw
tube resolution. These two parameters change
considerably with eccentricity.
The change in signal amplitude for various
eccentricities. By 400 micron eccentricity, the
amplitude has clearly increased by nearly 10.
The resolution is the width of the pulse height
distribution from Fe 55 X-rays as they are
converted in the straw tube.
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Eccentricity Results Continued
To find bent straws, acceptance tests will record
amplitude and resolution using Fe 55 X-rays at
six point along the length of the straw. This
profile can then be analyzed in order to
determine the quality of the straw. For this
reason, a controlled straw deformation has been
performed and the resulting signal amplitudes for
13 points along the straw have been recorded and
analyzed.
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Ellipticity Results
While eccentric wires are a more common problem,
it is important that straws with deformed wall
shapes can also be recognized and examined. Thus
straw tubes were elliptically deformed, and the
signal amplitude and straw resolution were
recorded for 11 points along the length of the
straw. These profiles could then be used to
characterize possible deformations encountered
during acceptance tests.
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Conclusions
Using multiple data samples, one can create a
reproducible relationship between amplitude
variations and resolution changes for both
eccentric and elliptic deformations. These
relations can be used when searching for deformed
straws and assessing straw quality. Note that
the elliptic data is still under analysis.
Summer Conclusion on Hardware Experiments I
was told to expect 90 set-up, 10 data
acquisition and analysis Are these statistics
accurate? Of 45 days, it took 2 days for data
collection, and 3 days for data analysis. So
11 of my time was spent retrieving and
analyzing data. Most days were spent building
the equipment, and debugging hardware in order to
create a working and usable experiment.
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Acknowledgements

• Mar Capeans and Peter Cwetanski
• Xavier Pons, Neil Dixon and Andreas Ekstroem
• Jean Krish, Homer Neal, and Jeremy Birnholtz
• CERN Summer Student Program, University of
  Michigan CERN REU, and NSF

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Questions?