Reducing the occupancies in the calorimeter endcaps of the clic detector
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Reducing the occupancies in the calorimeter endcaps of the CLIC detector . Suzanne van Dam Supervisor: André Sailer CERN, 6 March 2014. Introduction. Beam-beam interactions Background incoherent pairs Scatter in forward region of CLIC detector H igh occupancy in HCal.

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Reducing the occupancies in the calorimeter endcaps of the clic detector

Reducing the occupancies in the calorimeter endcaps of the CLIC detector

Suzanne van Dam

Supervisor: André Sailer

CERN, 6 March 2014


Introduction
Introduction

  • Beam-beam interactions

  • Background incoherent pairs

  • Scatter in forward region of CLIC detector

  • High occupancy in HCal

CERN-THESIS-2012-223


Occupancy reduction
Occupancy reduction

  • The high occupancy has to be reduced

  • Support tube can provide shielding

  • Optimize support tube material and thickness


Simulation of occupancy
Simulation of occupancy

  • Simulate background for each geometry

  • Estimate the occupancy

    • Need data from a few bunch trains (312 BX/train)

  • Find number of particles passing through support tube

    • Correlated to occupancy

    • Need data from ~10 BXs

  • Geometrical adaptations to the detector model:

    • Introduce a scoring plane around support tube

    • Make support tube geometry variable


Simulation of occupancy1
Simulation of occupancy

  • Simulate background for each geometry

  • Estimate the occupancy

    • Need data from a few bunch trains (312 BX/train)

  • Find number of particles passing through support tube

    • Correlated to occupancy

    • Need data from ~10 BXs

  • Geometrical adaptations to the detector model:

    • Introduced a scoring plane around support tube

    • Made support tube geometry variable through text file


Contributions to occupancy
Contributions to occupancy

Energy deposits in HCalendcap

  • Occupancy per particle type:

    • Photons and neutrons contribute

  • Compare to number of hits from different particles in the scoring plane:

    • Photons have a relatively large impact

  • Reflect this in the relation between hits in the scoring plane and the occupancy

Hits in scoring plane


Figure of merit
Figure of merit

  • To minimize the occupancy, minimize neutron (n) and photon (γ) hits (H) with a relative weight (w)

  • Assume linear dependence on each particle type

  • This can be expressed in a figure of merit (FOM):

  • Weights follow from the ratio of:

    • Number of energy deposits above threshold and within timing cut in the HCalendcap (N);

    • Number of hits in the scoring plane (H).


Energy
Energy

  • Energy spectrum for hits in the scoring plane

  • HCalendcap threshold is 300 keV


Support tube material
Support tube material

  • Iron

photons

neutrons


Support tube material1
Support tube material

  • Iron based:

    • Iron

    • Stainless steel

    • Cast iron

    • Borated steel

photons

neutrons


Support tube material2
Support tube material

  • Iron based:

    • Iron

    • Stainless steel

    • Cast iron

    • Borated steel

  • Neutron moderating and absorbing:

    • Pure polyethylene (PE)

    • PE + Li2CO3

    • PE + H3BO3

photons

neutrons


Support tube material3
Support tube material

  • Iron based:

    • Iron

    • Stainless steel

    • Cast iron

    • Borated steel

  • Neutron moderating and absorbing:

    • Pure polyethylene (PE)

    • PE + Li2CO3

    • PE + H3BO3

  • Short radiation length:

    • Tungsten

    • Lead

photons

neutrons


Combine materials
Combine materials

  • Polyethylene for neutron shielding

  • Iron-based materials for photon shielding

  • Tungsten for further photon shielding

  • To shield both photons and neutrons, materials should be combined.


Combine materials1
Combine materials

  • Polyethylene & stainless steel

Total thickness of support tube 100 mm


Combine materials2
Combine materials

  • Polyethylene & stainless steel

  • Tungsten & stainless steel

Total thickness of support tube 100 mm


Summary and conclusions
Summary and conclusions

  • The high occupancy due to incoherent pairs in the HCalEndcap is caused by neutrons and photons

  • Photons have relatively more impact on the occupancy

  • Minimization of the occupancy is based on minimizing the number of particles passing the support tube

  • Therefore a figure of merit is defined that reflects the higher impact of photons:

  • Simulations show that

    • Tungsten is suitable for photon shielding

    • Polyethylene is suitable for neutron shielding

    • To shield both neutrons and photons materials should be combined

    • A high contribution from photon shielding materials is needed


Outlook
Outlook

  • Maximize shielding by reducing inner radius of support tube

  • Use as much tungsten as structural strength allows

  • For neutron shielding add polyethylene to a structure of tungsten and stainless steel