An improvement of radiation hardness of CMS Hadron Endcap Calorimeters under increased LHC luminosity

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An improvement of radiation hardness of CMS
Hadron Endcap Calorimeters under increased LHC
luminosity

• Joint Institute for Nuclear Research, Dubna,
  Russia
• S.V. Afanasiev, S.E. Vasiliev, I.A. Golutvin,
  A.M. Makankin, A.I. Malakhov,
• P.V. Moisenz, V.A. Smirnov
• National Center for Particle and High Energy
  Physics, Minsk, Belarus
• I.F. Emeliantchik, A.V. Litomin, N.M. Shumeiko
• NSC Kharkov Institute of Physics and Technology,
  Kharkov, Ukraine
• L.G. Levchuk

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Radioactive exposure of HE detector.
Simulation of dose map (Gy per 500 fb-1) in HE
Scintillator tiles of HE, which are closer to the
beam, absorb the greater radioactive dose. Main
aspect is to provide operation of HE calorimeters
after upgrade phase II.
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Evaluation of dose in HE tiles
Normal operation of HE tiles up to integral
radiation level at 5 Mrad.
Radiation doses for period of time, which should
provide accumulation of experimental data for
integrated luminosity of 500 fb-1. It means 10
years of LHC operation. The most irradiated part
of HE corresponds to ? from 2.5 to 3.0 in the
first few layers of HE.
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Main factor of light loss

• Main factors of light loss with dose increase.
• Transmittance loss of scintillator (becomes
  yellow).
• Transmittance loss of WLS fiber.
• Degradation of scintillating ability.
• Reducing of conversion efficiency of WLS fiber.

Scintillator Kuraray SCSN81
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Scintillator irradiation
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Main concept
How to improve radiation hardness of HE
scintillators? We decided to improve light
collection from more irradiated tiles.
Proposed solution Divide tile to several strips.
Each strip (width W) has own WLS fiber in the
middle .
Advantages An average path of light inside a
strip becomes shorter. Length of each WLS fiber
becomes shorter. Losses of light
are decreased.
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Dependence from absorbed dose
Light output from irradiated sample
Degradation factor of scintillating ability
Attenuation factor in scintillator and its ?sc(D)
attenuation length
Attenuation factor in WLS fiber with length L and
its ?wls(D) attenuation length
Conversion efficiency of WLS fiber
Light output from non irradiated sample with
width W
Attenuation caused by optical OR. k
transmittance loss in one OR. N number of
stages of optical OR.
8 light inputs from WLS fibers
Light output from clear fiber go to megatile
optical connector
N 3 stages
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Test on electron beam
Radiation source is electron beam with E 4 Mev.
An irradiation of scintillator samples WLS
fibers with electrons of doses 0.5, 1, 5, 10 and
30 Mrad.
1/16
1/8
1/4
1/2
To define light attenuation factors with
different doses of irradiation.
Ten copies of each type. Radiachromic dosimeters
to measure absorbed dose (0.05-20 Mrad). Primary
check of transparency of radiachromic dosimeters.
Measurement of light yield of all samples.
Measure of transmittance loss in samples.
Measure of transmittance loss in WLS fibers.
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Dependence of signal amplitude vs. sample width
Results were normalized to the signal from the
tile (main sample) with the position of WLS
fiber as in the real tile of HE.
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Measurement results of attenuation factors
Dependence of WLS fiber attenuation length ?wls
vs absorbed dose
Dependence of scintillator attenuation length
?sc vs absorbed dose
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Measurement results of Jsc and Jwls
Degradation factor of scintillator light yield
Jsc vs absorbed dose
Dependence of conversion efficiency of WLS fiber
Jwls vs absorbed dose
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Introduction of optical OR
How to minimize the upgrade process of HE
megatiles? Just use as in original scheme one
clear fiber from one tile.
It means a necessity to combine the light coming
from several WLS fibers of tiles strips into one
clear fiber. We propose to use optical OR
scheme. kN - attenuation caused by optical
OR. k - transmittance loss in one OR. N -
number of stages of optical OR.
To Photo Detector
(PD) to PD
to PD to PD
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Test of optical OR
Scheme for measurement loss of light in optical
OR.
Three samples of optical OR scheme has been
made and tested. The best result of light loss
in optical OR scheme is k 0.7 Values of k
0.8 are quite affordable.
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Compare of light outputs A(D) of the upgraded and
standard options with equal absorbed dose
Light output from non irradiated sample S(WU) and
main tile S(WS) with width W
kN attenuation caused by opt OR k transmittance
loss in one OR. N number of stages of OR.
Attenuation length of scintillator ?sc(D)
Attenuation length of scintillator ?sc(D)
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Conclusions

• Series of measurements on several sets of SCSN81
  scintillator Y-11 WLS fiber with electron beam
  was performed and a set of experimental results
  was obtained
• Dependence of signal amplitude vs. the sample
  width.
• Transmittance loss in scintillator and its
  attenuation length in dependence of absorbed
  dose.
• Transmittance loss in WLS fiber and its
  attenuation length in dependence of absorbed
  dose.
• Degradation factor of scintillating ability in
  dependence of absorbed dose.
• Conversion efficiency of WLS fiber in dependence
  of absorbed dose.
• Possibility of combining several WLS
  fibers using the scheme optical OR.
• Making several pieces of optical OR and
  measurement of transmittance loss in one optical
  OR.
• Compare of light outputs of the upgraded and
  standard options with equal absorbed dose.
• It is shown that the proposed method will allow
  to increase the radiation hardness of most
  irradiated HE tiles up to 20 Mrad.

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Light yield with transmittance loss in one
optical OR 0.7
Measurements of light yield for all samples were
performed at the same conditions.
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Light yield with transmittance loss in one
optical OR k 0.7 and k 0.8
Measurements of light yield for all samples were
performed at the same conditions.
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Area of improvement of HE radiation hardness
Measurements of light yield for all samples were
performed at the same conditions.
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