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Production and quality control of the optical elements

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PRODUCTION AND QUALITY CONTROL OF CMS END CAP                             О
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    HADRON CALORIMRTER OPTICAL ELEMENTS                                           С




                           Victor KRYSHKIN
   9th Topical Seminar Innovative Particle and Radiation Detectors,
                         Siena, 24 May 2004
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                                                       INTRODUCTION                               О
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                                                                                                          С




    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         2        9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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           REQUIREMENTS TO CMS END CAP HADRON CALORIMETER                              О
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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   3   9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                 DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                                Д
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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   4   9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                  DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                           О
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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   5   9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                   DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                                          Д
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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    6              9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                   DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                                             О
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Cut in the absorber for photodetectors and                                                         TOWER NUMBER
electronics. Additional layer.
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                   HE that
significantly  worsen  the   combine                     energy
resolution.                                                             28
                                                                        29

                                                                               LAYER NUMBER
To correct the influence of dead                        material
introduced by support structure of EE.
                                                               A quadrant cross section view of calorimeter


 Production and quality control of CMS End cap hadron   7                     9th Topical Seminar, 24 May, 2004
 calorimeter optical elements, Kryshkin V.
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                  DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                                                    О
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                                                                 OPTICAL CONNECTORS

                                                           MEGATILE 1                                MEGATILE 2
   Each 200 sector is divided into two 100 parts
   and has odd and even megatiles.                                 1                 2
                                                                                         3           4


                                                                       16-1    16-2      16-3 16-4
   Trapezoidal shape megatiles are not mirror
   images because they         are located at                           17-1 17-2 17-3 17-4

   different depth (44 mm shift).                                        18-1 18-2 18-3 18-4

                                                                          19-1 19-2 19-3 19-4
   Towers and optical connectors of the same                              20-1 20-2 20-3 20-4
                                                                                                         TILE
   color are connected with fibers.                                            21             21

                                                                               22        22

   Dimensions of the towers correspond to                                       23       23

   dimensions of EE to simplify trigger.                                         24      24

                                                                                 25      25

                                                                                 26 26
                                                                                    27 27
                                                                                    28 28
                                                                                    29 29




Production and quality control of CMS End cap hadron   8                      9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                 DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                            О
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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   9   9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                DESIGN OF CALORIMETER AND OPTICAL ELEMENTS                                                                                  Д
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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                                                             a)
terminate fibers from tiles.                            LAYER 0 SCINTILLATOR   DURALUMINUM PLATE (1.0 mm)
                                                                                AIR GAP (1.8 mm)
                                                                                 TYVEK (0.17 mm)                                     OPTICAL FIBER
                                                                                   SCINTILLATOR (9 mm)


Two     connectors                    for   wire                                  TYVEK (0.17 mm)
radioactive source                     tubes to                                 AIR GAP (1.8 mm)
                                                                               DURALUMINUM PLATE (1.0 mm)

illuminate all tiles.
                                                        SCINTILLATOR OF LAYER 1-17
                                                                                               b)
One optical connector (for two                                                       DURALUMNUM PLATE (1.0 mm)

layers) – to fan-out UV light from
                                                                                      AIR GAP (1.8 mm)                               OPTICAL FIBER
                                                                                       TYVEK (0.17 mm)
                                                                                        SCINTILLATOR (4 mm)

laser to each tile.                                                                    TYVEK (0.17 mm)
                                                                                      DURAMINUM PLATE (1.0 mm)



                                                                                               c)
 Production and quality control of CMS End cap hadron           10                                          9th Topical Seminar, 24 May, 2004
 calorimeter optical elements, Kryshkin V.
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                                   INPUT CONTROL OF FIBERS                                 О
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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%.

       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   11      9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                   PRODUCTION AND CONTRO OF OPTICAL BUNDLES                                 Д
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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   12   9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                 PRODUCTION AND CONTRO OF OPTICAL BUNDLES                                                     Д
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 Distance from scintillator to photodetector
 varies between ~20 сm and 100 сm.
                                                            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.                                 150


 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.
                                                            100

 Two WLS fibers were spliced and the light                        0   200   400   600   800    1000 1200          1400
 yield was measured in dependence on
 distance.                                                                           L (mm)
 Light yield jump defines the loss on the                   Light yield in dependence on
 boundary. In average this value was about                  distance for spliced WLS fiber.
 5%.

Production and quality control of CMS End cap hadron   13                     9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                   PRODUCTION AND CONTRO OF OPTICAL BUNDLES                                               О
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Calorimeter has projective
geometry.           Scintillator




                                                       Light yield (a.u.)
dimensions are increasing
with depth and absorption of
light in scintillator and WLS
fibers is increasing.
To circumvent this effect the
                                                                             Layer
WLS fiber length for each
tower was the same and                                       Variation of light yield in towers in
defined by the fiber length                                  dependence on depth ( layer number).
for the scintillator of the last
layer.


Production and quality control of CMS End cap hadron   14                     9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                                                                                                    О
                    PRODUCTION AND CONTRO OF OPTICAL BUNDLES                                            Д
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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                    Normalized        light     yield
 fibers. Light exited in fibers was detected by
                                                            distribution for optical bundles
 PIN diodes.
                                                            .
 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   15               9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                  QUALITY CONTROL OF OPTICAL ELEMENTS                                        О
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         a                                                  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   16        9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                   QUALITY CONTROL OF OPTICAL ELEMENTS                                                  О
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With decreasing of tile size
increasing part of wire source




                                                       Rп/Rк
radiation exceeds the bounds
of scintillator and ratio Rw/Rc
also decreasing. The ratio is
used to transfer calibration
coefficients obtained with fixed                                          Tower
target beams to collider
installation.                                            Signal ratio for wire and collimated
                                                         radioactive sources for different
                                                         towers.




Production and quality control of CMS End cap hadron           17           9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                  QUALITY CONTROL OF OPTICAL ELEMENTS                                       О
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                         A                                  Absorber
                                                             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   18       9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                                      COMBINATORIAL ANALYSIS                               О
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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   19      9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                                                       SUMMARY                               О
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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       20    9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.
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                                                       SUMMARY                              О
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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       21    9th Topical Seminar, 24 May, 2004
calorimeter optical elements, Kryshkin V.

								
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