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PRODUCTION AND QUALITY CONTROL OF CMS END CAP
HADRON CALORIMRTER OPTICAL ELEMENTS
Victor KRYSHKIN
9th Topical Seminar Innovative Particle and Radiation Detectors,
Siena, 24 May 2004
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INTRODUCTION
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End cap hadron calorimeter (НЕ) of CMS (Compact Muon Solenoid)
detector consists of brass absorber plates interspersed with optical
elements and covers |1.3|≤≤|3.0|. We describe here:
• requirements to CMS End cap hadron calorimeter;
• calorimeter and optical elements design;
• fiber input control;
• production and quality control of optical bundles;
• control of optical elements;
• summary.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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REQUIREMENTS TO CMS END CAP HADRON CALORIMETER
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General requirements:
• absorber with minimal inter;
• minimal calorimeter length 10 inter;
• sampling must correspond to the required energy resolution;
• minimal dead zones to measure missing energy;
• high transverse granularity (must be similar to one of Ecal) to have
good spatial separation of 2 jet events and mass resolution;
• during the experiment – 10 years – the radiation hardiness must be
sufficient to withstand absorbed dose of 6 Mrad .
Calorimeter is placed inside of 4 Т magnet.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
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The calorimeter is fixed to stainless
steel plate. Electromagnetic calorimeter
(ЕЕ) with a preshower (SE) is fasten to the
front face of calorimeter.
The calorimeter absorber is self
supporting, has no dead zones and can be
many times assembled and disassembled –
important feature taking into account
necessity
for
transportation
and
dimensions (6 m diameter and 350 t
weight).
Calorimeter is divided into 18 sectors
200 each. A sector is divided into two parts.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
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Brass plates (70% Cu/ 30% Zn) are connected by bolts and collets (to
minimize a backlash). 9 mm gaps in the absorber for optical elements
(megatiles) for each half of the sector is shifted by ½ of the period (88
mm). In transverse direction the gaps are overlapped (16 mm) to
compensate the thickness of optical element frames (8 мм).
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
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Simulation shows that the calorimeter energy resolution
described as
 / E  120% / E  5%
does not determine the jet energy resolution defined by
other types of fluctuations.
The stochastic term defines sampling – 79 mm thick brass
plate.
5% constant term corresponds to 10% light collection
uniformity in depth.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
Cut in the absorber for photodetectors and
electronics. Additional layer.
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TOWER NUMBER
Layers of different color are read out separately to
optimize the coefficients in case of radiation
damage.
Tower 28 has additional transverse and
longitudinal segmentation to correct degradation
of most loaded part.
Points show tiles illuminated by UV laser.
Zero layer in front of HE is intended for improving
of
energy
resolution
operating
with
electromagnetic calorimeter (PbWO4).
Ratio e/ for EE much bigger than for
significantly
worsen
the
combine
resolution.
HE that
energy
To correct the influence of dead
introduced by support structure of EE.
material
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LAYER NUMBER
A quadrant cross section view of calorimeter
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calorimeter optical elements, Kryshkin V.
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
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OPTICAL CONNECTORS
MEGATILE 1
Each 200 sector is divided into two 100 parts
and has odd and even megatiles.
Trapezoidal shape megatiles are not mirror
images because they
are located at
different depth (44 mm shift).
MEGATILE 2
1
2
16-1
16-2
3
4
16-3 16-4
17-1 17-2 17-3 17-4
18-1 18-2 18-3 18-4
19-1 19-2 19-3 19-4
Towers and optical connectors of the same
color are connected with fibers.
Dimensions of the towers correspond to
dimensions of EE to simplify trigger.
20-1 20-2 20-3 20-4
TILE
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23
23
24
24
25
25
26 26
27 27
28 28
29 29
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
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a) design of tiles;
b) 1-17 layers, Kurary SCSN81 scintillator 4 mm thick, 1 fiber;
c) 0 layer, Bicron scintillator BC-408 9 mm thick, 2 fibers.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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9th Topical Seminar, 24 May, 2004
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DESIGN OF CALORIMETER AND OPTICAL ELEMENTS
Tiles wrapped into reflective
paper and into light tightening
material are inserted into box
limited from 3 sides by brass
planks and fixed above and below
by 1 mm thick duraluminum
plates.
Optical
connectors
terminate fibers from tiles.
Two
connectors
radioactive source
illuminate all tiles.
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a)
LAYER 0 SCINTILLATOR
for
wire
tubes to
DURALUMINUM PLATE (1.0 mm)
AIR GAP (1.8 mm)
TYVEK (0.17 mm)
SCINTILLATOR (9 mm)
OPTICAL FIBER
TYVEK (0.17 mm)
AIR GAP (1.8 mm)
DURALUMINUM PLATE (1.0 mm)
b)
One optical connector (for two
layers) – to fan-out UV light from
laser to each tile.
SCINTILLATOR OF LAYER 1-17
DURALUMNUM PLATE (1.0 mm)
AIR GAP (1.8 mm)
TYVEK (0.17 mm)
SCINTILLATOR (4 mm)
OPTICAL FIBER
TYVEK (0.17 mm)
DURAMINUM PLATE (1.0 mm)
c)
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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INPUT CONTROL OF FIBERS
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Quality control of Kuraray Y11 optical fibers (WLS and clear) :
fiber diameter is 0.94 мм 0.02 мм;
no mechanical defects (cracks or scratches);
flexibility (no cracks for 5 cm bending radius);
for m. i. p. Np.e.= 3 with WLS fiber 25 сm length and scintillator
with dimensions 50 mm x 50 mm x 1 mm;
• attenuation length of WLS and clear fibers must be close to
standard fibers;
• variation of parameters (light yield and attenuation length) from
batch to batch must be within 10%.
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Fibers that passed the control were cut according to table and used
for production of optical bundles.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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PRODUCTION AND CONTRO OF OPTICAL BUNDLES
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The fibers were machined from both ends by flying diamond
cutter and the surface quality was controlled by a
microscope.
One end of WLS fibers was mirrored by aluminum
sputtering and covered with varnish. Coefficient of
reflection was measured for each batch of 200 fibers: light
yield of 10 fibers illuminated with UV source was measured.
Then the aluminized ends were cut at 450 , covered by black
paint and measured again. If the reflection coefficient was
≥85% the batch was used for further production.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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PRODUCTION AND CONTRO OF OPTICAL BUNDLES
Distance from scintillator to photodetector
varies between ~20 сm and 100 сm.
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N
200
If all path to photodetector is made of WLS
fibers then there will be appriciable
difference of light collection from the first
and the last scintillator.
WLS fibers exiting from scintillators are
thermally spliced to clear fibers other end of
which was glued into optical connector and
machined by diamond flying cutter.
Two WLS fibers were spliced and the light
yield was measured in dependence on
distance.
Light yield jump defines the loss on the
boundary. In average this value was about
5%.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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150
100
0
200
400
600
800
1000 1200
1400
L (mm)
Light yield in dependence on
distance for spliced WLS fiber.
9th Topical Seminar, 24 May, 2004
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Calorimeter has projective
geometry.
Scintillator
dimensions are increasing
with depth and absorption of
light in scintillator and WLS
fibers is increasing.
To circumvent this effect the
WLS fiber length for each
tower was the same and
defined by the fiber length
for the scintillator of the last
layer.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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Light yield (a.u.)
PRODUCTION AND CONTRO OF OPTICAL BUNDLES
Layer
Variation of light yield in towers in
dependence on depth ( layer number).
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PRODUCTION AND CONTRO OF OPTICAL BUNDLES
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2-9 fibers were glued into optical connectors
(2880 pieces). Quality control of the bundles
was carried out with a test bench which was
also used for quality control of splicing and
mirroring of fiber ends.
The fibers were placed into grooves
machined in aluminum kept by vacuum
pump.
A fluorescent lamp was moving along the
fibers. Light exited in fibers was detected by
PIN diodes.
Normalized
light
yield
distribution for optical bundles
.
The data are compared with standard and if
they are within allowed range the bundle is
used for further assemblage.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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QUALITY CONTROL OF OPTICAL ELEMENTS
a
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b
PM current from tiles vs. distance a) collimated source and b) wire source.
Assembled megatiles were controlled with collimated radioactive source
60Co. Light signals from each scintillator were fed by optical cable to
PMTs. The current from each PMT along with radioactive source
coordinates was recorded in data base. After installation of megatiles into
absorber control is realized with wire source. Therefore measurements
with wire source were also made using the test bench.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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With decreasing of tile size
increasing part of wire source
radiation exceeds the bounds
of scintillator and ratio Rw/Rc
also decreasing. The ratio is
used to transfer calibration
coefficients obtained with fixed
target beams to collider
installation.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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Rп/Rк
QUALITY CONTROL OF OPTICAL ELEMENTS
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Tower
Signal ratio for wire and collimated
radioactive sources for different
towers.
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QUALITY CONTROL OF OPTICAL ELEMENTS
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Absorber
A
No absorber
R (0.1 mm)
Influence of absorber : due to backscattering (albedo) wire
radioactive source rises 9% if a scintillator is surrounded by
brass plates 4 cm thick each.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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COMBINATORIAL ANALYSIS
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Normalized distribution for collimated
radioactive source variation of light
yield in depth for all towers (1368
megatiles). The distribution is well
described by Gaussian with =10%.
Further improvements was achieved
by
combinatorial
analysis
–
calculation of megatile combination
providing minimal variation of light
yield.
The analysis allows to reduce it to
=8%.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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SUMMARY
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• Hadron calorimeter without dead zone was designed.
• Optical elements are easy to produce and assemble,
have rigid structure to install in any position.
• Thorough quality control of optical elements (1368
megatiles containing 21096 scintillators) at all stages
allowed to minimize variation of light yield in towers.
• Further improvement was achieved by combinatorial
analysis.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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SUMMARY
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Now megatiles are transported to CERN, again tested with collimated
and wire sources, part of them calibrated with fixed target beam and all
of them inserted into absorber of both End caps.
Production and quality control of CMS End cap hadron
calorimeter optical elements, Kryshkin V.
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