An improvement of radiation hardness of CMS Hadron

Endcap Calorimeters under increased LHC luminosity

Joint Institute for Nuclear Research, Dubna, RussiaS.V. Afanasiev, S.E. Vasiliev, I.A. Golutvin, A.M. Makankin, A.I. Malakhov,

P.V. Moisenz, V.A. SmirnovNational Center for Particle and High Energy Physics, Minsk, Belarus

I.F. Emeliantchik, A.V. Litomin, N.M. ShumeikoNSC Kharkov Institute of Physics and Technology, Kharkov, Ukraine

L.G. Levchuk

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Radioactive exposure of HE detector.

3.000

2.868

2.650

2.500

2.322

2.172

2.043

1.930

1.830

1.740

1.653

1.5661.479 1.392 1.305

3.000

2.5002.3222.1722.0431.930

1.8301.7401.653

1.566

1.479

1.392

2.868

1.305

2.650

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.

Simulation of dose map (Gy per 500 fb-1) in HE

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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 η from 2.5 to 3.0 in the first few layers of HE.

Evaluation of dose in HE tiles

Normal operation of HE tiles up to integral radiation level at 5 Mrad.

R (cm)

3.000

2.868

2.650

2.500

η

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Main factor of light loss

Main factors of light loss with dose increase.

1. Transmittance loss of scintillator (becomes yellow).2. Transmittance loss of WLS fiber.3. Degradation of scintillating ability. 4. Reducing of conversion efficiency of WLS fiber.

Scintillator Kuraray SCSN81

WLS fiber Kuraray Y-11.

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Scintillator irradiation

Our recent measurements of scintillator + WLS fiber samples

irradiated by electrons (E ≈ 4 MeV)SCSN-81 & Y11

10cm x 10cm x 0.4cm

0.1 0.5 1

Rel

ativ

e lig

ht y

ield

1 10Absorbed dose (Mrad)

0.1 5

HCAL TDRSCSN-81 & BCF-91A 10cm x 10cm x 0.4cm

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Main concept

How to improve radiation hardness of HE scintillators? We decided to improve light collection from more irradiated tiles.

Advantages:An average path of light inside a strip becomes shorter. Length of each WLS fiber becomes shorter. Losses of light are decreased.

Proposed solution:Divide tile to several strips. Each strip (width W) has own WLS fiber in the middle .

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Dependence from absorbed dose

DJD wls scwlsscN J(D))L/(exp(D))(W/exp k(W) SA(D)

Light output from irradiated sample

Light output from non irradiated sample with width W

Attenuation factor in scintillator and its λsc(D) attenuation length

Attenuation factor in WLS fiber with length L and its λwls(D) attenuation length

Degradation factor of scintillating ability

Conversion efficiency of WLS fiber

Attenuation caused byoptical “OR”.k transmittance lossin one “OR”.N number of stagesof optical “OR”.

8 light inputs from WLS fibers

Light output from clearfiber go to megatile optical connector

N = 3 stages

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Test on electron beam

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.

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.

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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.

3.2

2.2

1.1

0.6

0

1

2

3

4

0 7 14 21 28 35 42 49 56

Sign

al, a

.u.

Width of strip, (mm)

Output signal from strip, S(W)

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Measurement results of attenuation factors

Absorbed dose (Mrad)0.5 1 5 10 30

Absorbed dose (Mrad)

Dependence of scintillator attenuation length λsc vs absorbed dose

Dependence of WLS fiber attenuation length λwls vs absorbed dose

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Measurement results of Jsc and Jwls

Absorbed dose (Mrad)Absorbed dose (Mrad)

Degradation factor of scintillatorlight 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 tile’s 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”. Surfaces are cut, polished and spliced

Inputs: 16 WLS fibers 8 WLS 4 WLS 2 WLS

Attenuation: k4 k3 k2 k1

# of stages 4 3 2 1

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 ≈ 0.7Values of k ≈ 0.8 are quite affordable.

LED

WLS fibers

Clear fiber

Photo Detector position1

Photo Detector position2

L=14 cm

L=14 cm

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Compare of light outputs A(D) of the upgraded and standard options with equal absorbed dose

(D) L- L

(D) W

212expk

)(W S)(W S

(D)A(D)A G(D)

wls

us

sc

sN

NN

s

u

s

u

Light output from non irradiated sample S(WU) and main tile S(WS) with width W

Attenuation length of scintillator λsc(D)

Attenuation length of scintillator λsc(D)

kN attenuation caused by opt “OR”k transmittance loss in one “OR”.N number of stages of “OR”.

0.5 1 5 10 30Absorbed dose (Mrad)

168

4

2

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Conclusions

1. 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.2. 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.

0.1 0.5 1 5 10 30Absorbed dose (Mrad)

Main sample

Assembly – 16 strips

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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.

0.1 0.5 1 5 10 30Absorbed dose (Mrad)

Main sample

Assembly – 16 strips

k ~ 0.7

k ~ 0.8

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Area of improvement of HE radiation hardness

Measurements of light yield for all samples were performed at the same conditions.

0.1 0.5 1 5 10 30Absorbed dose (Mrad)

Main sample

Assembly – 16 strips

k ~ 0.7

k ~ 0.8