1. 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

2. 6/2/2014Vitaly Smirnov - Alushta20122 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 1.566 1.4791.3921.305 3.000 2.500 2.322 2.172 2.043 1.930 1.830 1.740 1.653 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

3. 6/2/2014Vitaly Smirnov - Alushta20123 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 2.5002.500 η

4. 6/2/2014Vitaly Smirnov - Alushta20124 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.

5. 6/2/2014Vitaly Smirnov - Alushta20125 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 0.10.51 Relative light yield 110 Absorbed dose (Mrad) 0.15 HCAL TDR SCSN-81 & BCF-91A 10cm x 10cm x 0.4cm

6. 6/2/2014Vitaly Smirnov - Alushta20126 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.

7. 6/2/2014Vitaly Smirnov - Alushta20127 Dependence from absorbed dose Light output from irradiated sample Light output from non irradiated sample with width W Attenuation factor in scintillator and its λ sc (D) attenuation length Attenuation factor in WLS fiber with length L and its λ wls (D) attenuation length Degradation factor of scintillating ability Conversion efficiency of WLS fiber 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

8. 6/2/2014Vitaly Smirnov - Alushta20128 Test on electron beam 1/161/81/41/2 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.

9. 6/2/2014Vitaly Smirnov - Alushta20129 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., S(W)

10. 6/2/2014Vitaly Smirnov - Alushta201210 Measurement results of attenuation factors Absorbed dose (Mrad) 0.5151030 Λ sc (cm) λ wls (cm) Absorbed dose (Mrad) Dependence of scintillator attenuation length λ sc vs absorbed dose Dependence of WLS fiber attenuation length λ wls vs absorbed dose

11. 6/2/2014Vitaly Smirnov - Alushta201211 Measurement results of J sc and J wls Absorbed dose (Mrad) J wls =A/A 0 Absorbed dose (Mrad) J sc =A/A 0 Degradation factor of scintillator light yield J sc vs absorbed dose Dependence of conversion efficiency of WLS fiber J wls vs absorbed dose

12. 6/2/2014Vitaly Smirnov - Alushta201212 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. k N - 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: k 4 k 3 k 2 k 1 # of stages 4 3 2 1 To Photo Detector (PD) to PD to PD to PD

13. 6/2/2014Vitaly Smirnov - Alushta201213 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. LED WLS fibers Clear fiber Photo Detector position1 Photo Detector position2 L=14 cm

14. 6/2/2014Vitaly Smirnov - Alushta201214 Compare of light outputs A(D) of the upgraded and standard options with equal absorbed dose Light output from non irradiated sample S(W U ) and main tile S(W S ) with width W Attenuation length of scintillator λ sc (D) k N attenuation caused by opt OR k transmittance loss in one OR. N number of stages of OR. 0.5 1 51030 Absorbed dose (Mrad) 16 8 4 2

15. 6/2/2014Vitaly Smirnov - Alushta201215 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.

16. 6/2/2014Vitaly Smirnov - Alushta201216 Light yield with transmittance loss in one optical OR ~ 0.7 Measurements of light yield for all samples were performed at the same conditions. 0.10.5151030 Absorbed dose (Mrad) Main sample Assembly – 16 strips

17. 6/2/2014Vitaly Smirnov - Alushta201217 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. 0.10.5151030 Absorbed dose (Mrad) Main sample Assembly – 16 strips k ~ 0.7 k ~ 0.8

18. 6/2/2014Vitaly Smirnov - Alushta201218 Area of improvement of HE radiation hardness Measurements of light yield for all samples were performed at the same conditions. 0.10.5151030 Absorbed dose (Mrad) Main sample Assembly – 16 strips k ~ 0.7 k ~ 0.8