APS POSTER

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APS POSTER
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Introduction The Large Hadron Collider (LHC)
will operate at 14 TeV center of mass energy with
proton proton collisions every 25 ns. Compact
Muon Solenoid is one of the detectors at the LHC.
Its Hadronic Calorimeter is composed of three
parts HB (Barrel), HE (Endcap) and HF (Forward).
Hadronic Endcap (HE) is a sampling calorimeter
with 50 mm thick copper absorber interleaved with
4 mm thick scintillator plates in the original
design. After a few years of run, the LHC will be
upgraded to operate at 10 times higher luminosity
(L1035 cm-2 s-1) allowing new physics
discoveries. This period is called superLHC
(SLHC). The lifetime radiation dose at the HE
Calorimeter will increase from 2.5 MRad to 25
MRad. The scintillator plates used in the
original design of HE will lose their efficiency
due to high radiation. As a solution to the
radiation damage problem at the SLHC conditions,
we propose to substitute scintillators by quartz
plates. They will not be affected by the high
radiation, but with quartz plates, the light
comes from Cerenkov radiation which produces 100
times less light than scintillation. Our aim is
to find an efficient way to collect light from
quartz plates. At the University of Iowa, we
tested and simulated different sizes of quartz
plates with different fiber geometries embedded
in them to obtain maximum light.
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Radiation Hardness
Tests Seven sets of quartz in the form of fiber
are irradiated in Argonne IPNS for 313 hours. The
test setup is shown in Figure 1. The fibers were
tested for optical degradation before and after
17.6 Mrad of neutron and 73.5 Mrad of gamma
radiation. Polymicro manufactured a special
radiation hard solarization quartz plate. The
response of this plate to the radiation can be
seen in Figure 2.
Figure 1
Figure 2
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• Light Collection Tests
• We tested HE scintillator, UVT plates, different
  sizes of low OH and high OH quartz plates using
  different beams and different fiber geometries.
• Figure 3 shows the results of the tests performed
  at Fermilab with 120 GeV proton beam using
  different thicknesses of iron as the absorber
  material.

The original HE fiber geometry gave the worst
results. Collected Cerenkov light was at around 8
for some of the plates.
Figure 3
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The graph below shows the results of the second
tests performed at Fermilab. 3 GE quartz plates ,
6 high OH and 4 low OH Polymicro quartz plates
(10 cm x 10 cm) are put in front of 3 different
beam energies 16 GeV, 66 GeV and 120 GeV.
Figure 4
According to these tests, low OH collects
slightly more light than high OH. Smaller plates
size gives better results than bigger plate size.
By reading from both ends of the fibers, it is
possible to obtain 30 more light.
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When the unfocussed beam is sprayed to the
plates, we collected 20 of the HE plate. The
graph below shows the results of this test.
Plate Numbers 1 - Low OH Y Shape 2 - Low
OH HE Shape 3 - Low OH HE Shape 2 Fiber 4 - Low
OH S Shape 5 - High OH Y Shape 6 - High OH S
Shape 2 Fiber 7 - High OH S Shape 8 - High OH
HE Shape 9 - UVT and Quartz 10 -Quartz-Quartz 11
-Liquid WS 12 - UVT-GWSF 13 - High OH PEACE
Shape 14 - Original HE Plate
Figure 5
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Surface Uniformity Tests We
performed bench tests on all quartz fiber
geometries for surface light collection
non-uniformities using UV-LED (380 nm), Nitrogen
Laser (337 nm), and Mercury lamp. We concluded
that S-Shape gives more uniform signal.
(Non-uniformity is around 10 ). All the other
fiber geometries have a surface non-uniformity
around 60 . Figure 5 is the result of the
surface uniformity tests performed on the quartz
plate with Y Shape fiber geometry. z - axis
gives the amount of light collected.
Figure 6
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New Fiber Geometry To
address the light collection efficiency and
uniformity issues we designed a new geometry (see
Figure 6). It has 9 fibers, with 1 mm diameter,
placed 4 cm apart from each other. We prepared 5
mm thick quartz and UVT plates with the
dimensions of 20 cm x 20 cm. We tested them at
Fermilab Meson Test area, on February 2006. Tests
show that using this new geometry, it is possible
to collect light up to 70-80 of the original HE
plate. The blue line in Figure 8 is the light
collection ratio of the new geometry versus the
HE geometry obtained using 120 GeV positive
beam.
Figure 7
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Figure 8
Blue line is for 120 GeV positive beam. Pink line
gives the results for 66 GeV positive beam. Light
collection efficiency drops by around 20 with
decreasing beam energy.
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Different Fiber Geometries in Quartz
HE Geometry
S-Shape
Y-Shape
O-Shape
SO Shape
PEACE Shape
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Simulations
We used GEANT 4.7.1 in our simulations.
WaveLength Shifting (WLS) fiber, Bicron 91a, is
embedded in the quartz plate. Quartz plates are
wrapped with reflecting material of 95
efficiency. The Cerenkov photons reaching the
PhotoMultiplierTube (PMT) are counted. Currently
UVA, UVB regions are included (gt 280 nm). Figure
9 is an example of a simulated plate with O
shaped fiber. Cerenkov Photons are shown in
green. Photons emitted by WLS process are shown
in red.
Figure 9
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According to the first simulations the number of
Cerenkov photons created in quartz is 1 - 2
of the number of scintillation photons in a
regular HE plate (see Table 1). These resuts are
for plates without any fiber embedded in them.
The beam used is 120 GeV proton beam. Absorber
materials with different thicknesses are put in
front of the plates. At the end of our study,
using different fiber geometries, plate sizes and
beam energies, we were able to reach up to 75 -
80 of the scintillation photons.
Table 1
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We simulated the collected light with 4 GeV
electron beam and counted the number of
wavelength shifted photons reaching the PMT. The
figure on the left is the simulation of the plate
with S shaped fiber geometry. Y - shape has a
better light yield compared to S and O
geometries (O S Y 1 9.9 11.4) S -
shape has the best surface uniformity on light
collection O - shape Max/Min 614/14 44
RMS/Mean 0.62 S - shape Max/Min 253/48 5
RMS/Mean 0.36 Y - shape Max/Min 170/21 8
RMS/Mean 0.52
Figure 10
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Conclusion and Future Plans We have focused on
light collection techniques. We started from 1
photon production ratio with respect to the
original HE scintillators. At the latest design
we increased the Cerenkov signal from a quartz
plate to almost 75 of the original HE
scintillator. Using different fiber geometries,
making the quartz thicker (5-6 mm), and smaller
(10 cm x 10 cm) increased our light collection.
For more light we should increase the amount of
fiber in the plates. Polymicros special
production of solarization quartz is radiation
hard. We used plastic WLS fiber. We have not
tried a radiation hard WLS fiber. Increasing the
fiber diameter improved the light collection. The
simulations show that light collection uniformity
varies drastically with changing fiber
geometries. We believe the new geometry will give
the most uniform results. The generation 1
Quartz Plate Calorimeter prototype is being built
with the NEW fiber geometry, based on the
information we collected during these RD
studies. CHECK POSTER 00075 FOR MORE
INFORMATION ON THE CALORIMETER PROTOTYPE!?