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