reducing the occupancies in the calorimeter endcaps of the clic detector
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Reducing the occupancies in the calorimeter endcaps of the CLIC detector Suzanne van DamSupervisor: André Sailer
CERN, 6 March 2014
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Introduction• Beam-beam interactions• Background incoherent pairs• Scatter in forward region of CLIC detector • High occupancy in HCal
Suzanne van Dam, 6 March 2014
CERN-THESIS-2012-223
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Occupancy reduction
Suzanne van Dam, 6 March 2014
• The high occupancy has to be reduced• Support tube can provide shielding• Optimize support tube material and thickness
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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
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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
Suzanne van Dam, 6 March 2014
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Contributions to occupancy • 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
Suzanne van Dam, 6 March 2014
Energy deposits in HCal endcap
Hits in scoring plane
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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 HCal endcap (N);– Number of hits in the scoring plane (H).
Suzanne van Dam, 6 March 2014
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Energy• Energy spectrum for hits in the scoring plane• HCal endcap threshold is 300 keV
Suzanne van Dam, 6 March 2014
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Support tube material• Iron
Suzanne van Dam, 6 March 2014
photons
neutrons
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• Iron based:– Iron– Stainless steel– Cast iron– Borated steel
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Support tube materialphotons
neutrons
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• Iron based:– Iron– Stainless steel– Cast iron– Borated steel
• Neutron moderating and absorbing:– Pure polyethylene (PE)– PE + Li2CO3– PE + H3BO3
Suzanne van Dam, 6 March 2014 9
Support tube materialphotons
neutrons
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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
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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.
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Combine materials• Polyethylene & stainless steel
Suzanne van Dam, 6 March 2014 11Total thickness of support tube 100 mm
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Combine materials• Polyethylene & stainless steel
• Tungsten & stainless steel
Suzanne van Dam, 6 March 2014 11Total thickness of support tube 100 mm
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Summary and conclusions• The high occupancy due to incoherent pairs in the HCal Endcap 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
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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
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