ATLAS Transition Radiation Tracker TRT

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ATLAS Transition Radiation Tracker (TRT) By
Byron Johns
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What is the ATLAS TRT?

• Tracks particles in a magnetic field to measure
  momentum.
• Detects transition radiation to identify
  particles.
• When protons collide, other particles can be
  created, leaving tracks. Each collision is an
  event.
• The tracks from each event are electronically
  recorded .
• Analysis of the events may lead to discovery of
  a new type of particle.

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Who deals with this stuff?!

• Hampton University is a partner in the ATLAS
  experiment at CERN (European Organization for
  Nuclear Research).
• We are helping to build one of the detector
  systems.
• One of the biggest experiments being built today.
• Last October, a serious flaw in the design was
  discovered
• Hampton must help fix the problem...

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How does this thang work?

• 420,000 detectors are inside to detect passage of
  the charged particles. The TRT detectors are
  drift tubes.
• Drift tubes - consist of a plastic straw-like
  tube, with a thin tungsten wire stretched down
  the center.
• Amplifiers placed at end of each wire pick up
  electric signal from wire.
• Signal caused by ionization due to passage of the
  particle.

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What Else?

• Tubes are filled with a gas Xe-CO2-CF4 (xenon,
  carbon dioxide, carbon tetrafluoride) that can be
  easily ionized by passage of particles.
• High voltage between straw and wire increase
  amount of ionization for amplifier to pick up.
• By collecting all the data from the tubes,
  particle paths in space can be reconstructed.

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Inside the Atlas Detector Model
Beam Pipe runs along the center of the detector
and carries the beam of protons. Protons
traveling in opposite direction through the pipe
collide at the middle of the detector Tracking
Detector filled with highly segmented sensing
devices made from strips of silicon so that
charged particle trajectories can be accurately
determined Muon Detectors only muons and
neutrinos get this far the muons are detected,
but the neutrinos escape. Hadron Calorimeter
measures the total energy of hadrons Solenoidal
Magnet large coil of wire wound cylindrically
to generate a straight uniform magnetic field
inside the coil. Electromagnetic Calorimeter
measures the total energy of e, e-, and photons.
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Get to the problem already!

• The thin wire is split in two parts connected by
  an insulating wire joint.
• This results in a lesser (half) number of pulses
  for the amplifiers to handle.
• Need a strong wire joint to sustain 60g tension
  (0.588N) for 10 years (planned length of ATLAS
  experiment).
• The first design has failed an important test.
  We must test a new design in 6 months, so
  construction can proceed.

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Previous Test(glass wire joint Duke design)

• Top Manufactured glass wire joint
• Middle glass wire joint before wire insertion
• Bottom Glass joint corroded to failure after
  test in realistic conditions for only two weeks!

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Whats That Joint Look Like?
Hampton design chosen! Wires are epoxy glued into
a plastic tube. Type A - wire placed in joint
straight Type B - Wire placed in joint with knots
on end for stronger hold.
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What Needs To Be Tested?

• Need to know if the new design will hold a wire
  tension of 60 g for ten years. (Note g is SI
  symbol for grams.)
• Do shorter tests (6 mos.) under higher tensions
  (90 g and 140 g), looking for loss of tension or
  joint slip or stretching.
• The 90-g test is a tension test -- measure the
  tension in 11 wires and look for changes over
  time due to joint.
• Temperature variation is one source of change in
  tension, due to different expansion of aluminum
  frame and tungsten wire. This effect must be
  corrected for in analyzing the data.

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Current Tests(pictures are COOL!)
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Principle of Tension Measurement - 1

• Stretched wire has a resonant frequency that
  depends on the tension
• When the wire is driven by an oscillating force,
  it will have maximum amplitude of oscillation at
  its resonant frequency.
• Detect the amplitude electrically, by using the
  varying capacitance between the wire and a plate
  maintained at constant voltage.

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Principle of Tension Measurement - 2
Oscillator/Amp (adjustable frequency)
speaker
Oscillo-scope
Capacitance between wire and plate
Constant Voltage (500V)
q CV C varies, V is fixed, so q varies. So a
current i flows in resistance R (in scope),
generating a voltage variation displayed by scope
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Test Setup

• Loudspeaker used to vibrate each wire to its
  resonant frequency.
• Observer adjusts frequency to get maximum
  amplitude of signal
• Time, resonant frequency of each wire, and
  temperature of aluminum base is recorded.
• Tension can be calculated from these measurements

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Calculations

• ?We have ? (T/?)1/2 ?, and ? ? ?, where
• is speed of wave on wire, T is tension, ? is
  wire mass / unit length, ? is frequency of wave,
  ? is wavelength.
• So ? (T/?)1/2 / ?
• Solve for T (tension in wires) to find the
  tension in the wires at each wires resonance
  frequency.
• Correct tension for temperature (see next slide)

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Data for finding temperature correction
Slope of each data set (see lines) gives
correction to be used in correcting each reading
to a standard temperature (correction will be
slope x temperature difference).
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Results (temperature corrected)
This plot shows results from the first three
days. Although there are variations, there does
not seem to be a general trend. The variations
may be due to different individuals making
different judgements as to resonant frequency
(observer bias).
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Another Test Recently Begun

• Wires are hung with 140g (1.372N) to test further
  strength of wire joint.
• Under this tension, it is known that some wires
  will break in time, but we are not concerned with
  that, just with the joint.
• So far, no joints have broken.
• Test will continue.

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Conclusions

• New design has so far passed the tests
• Tests need to continue over several months to be
  sure that good performance is maintained
• Other tests are needed and will be done,
  including tests in LHC conditions (CF4 gas, high
  voltage, etc.)

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Shout Outs!

• I would like to acknowledge those who helped me
  during this project
• Dr. Kenneth McFarlane
• Dr. Baker

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Any Questions?(Dont Ask Me!)
Go to http//pdg.lbl.gov/atlas/index.html
Thank You. You may now eat your PIZZA!