Post on 31-Dec-2015
Excess Radiation Damage of CMS Endcap Hadron Calorimeter and “Finger” Structure of Tiles as a Possible Method of Radiation Hardness
Increasing
I.Emeliantchik,CMS RDMS Collaboration
National Center of Particle and High Energy PhysicsBelorussian State University
International School-SeminarThe Actual Problems of Microworld Physics
Belarus, GomelJuly 26 - August 7, 2015
HCAL Radiation Hardness,Predicted and Real
CMS HCAL TDR prediction
CMS experimental result 2012(laser data)
Attempts to reproduce plasticbehavior at different irradiationconditions
Goals of Our Radiation Research
Two goals were set:• to explain the contradiction between expected and real
radiation damage of plastic scintillator;• to propose a method to improve radiation hardness
In current state the calorimeter will not even withstand the expected term ofoperation with current luminosity, not speaking about High Luminosity
Importance of Dose Rate
E. Biagtan, E. Goldberg et al., "Effect of gamma radiation dose rate on the light output of commercial polymer scintillators", NIM B93 (1994) p. 296-301
Dose rate influence was researched earlier, but that wasn’t taken into considerationduring HCAL developing
Production of Tiles
Tiles of SCSN-81Milling cutters for shifter grooves
Most radiation loaded tiles (sigma-tile #29) were produced using the samedesign documentation as in current calorimeter
Irradiation of tiles
• Tiles irradiation was done at gamma-installation UGU-240 of the Institute of Nuclear Energy Research – Sosny of National Academy of Science of Belarus.
• The installation is a radioactive source 60Co with activity 110 kCi, which can be submerged in water for the time of sample setting.
• The operative zone is a room 4 4 m2, in which one can walk freely (while the source is submerged), selecting a position with proper dose rate.
• We have chosen positions with dose rates close to real ones at working calorimeter.
• The light output was measured at JINR.
Explanation of excess degradation of plastic scintillator
Extrapolation of the obtained results to the dose rate of the first stage of calorimeter work (30 fbarn-1) gives light output decreasing comparable with observed one.
Graph drawing in semi-logarithmic frame of reference allows linear fitting
Radiation Hardness Improvement with Help of Additional Segmentation of Radiation Loaded Tiles
Existing segmentation Proposed segmentation
Radiation hardness improves due to decrease of the distance of light passing through the dim plastic
Number of photosensors is increasing, but SiPM (which will be implementedanyway) are very miniature, so it is not a problem
Production and Irradiation of Tile Segments
Tile segments were made and irradiated with doses up to 25 Mrad.Measurements had shown that the calorimeter in this configuration will withstand the whole term of operation in the mode of High Luminocity (3000 fbarn-1)
Current Version of Endcap Calorimeter for High Luminosity
Silicon ECAL Endcap
Silicon Forward HCAL Endcap Plastic Backward HCAL Endcap
Conclusion
• Excess plastic scintillator degradation is explained• New method of calorimeter radiation hardness improvement is proposed