03/22/2007 HCal Electronics Meeting

HO LIGHT GUIDE SIMULATIONS

Justin Parsons, University of Iowa Jim Freeman, FNAL

HO LIGHT GUIDE SIMULATIONS

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03/22/2007 HCal Electronics Meeting

Outline

• Problem and proposed solution• Light guide material, and geometry • Simulation software : LITRANI• Testing the software• Simulations• Results and future plans

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03/22/2007 HCal Electronics Meeting

Motivation for Simulations

• HO HPDs must be replaced• SiPMs are best option but are not equal in

active area or shape of HPDs

• Need a LG which will couple fiber bundle with SiPM

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03/22/2007 HCal Electronics Meeting

Material of Light Guide

• Bench tests @ Iowa show Mylar and HEM to be not rad hard enough– 17% reduction in eff after 10Mrad exposure IEEE Transactions on Nuclear Science, Vol. 53, No. 3, 1547

• Two options, Aluminum or “German Mylar” (HF)• Chose Al for these simulations

– Most common light guide material– May be processed to prevent oxidation and polished to

improve reflectivity– Easy to work with

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03/22/2007 HCal Electronics Meeting

Geometry and Source• Source emits at 520nm, laser or fiber with 30deg aperture• SiPM active area is 4.41mm2 => Ru=1.485mm

• Fiber bundle diameter is 3.5mm => RL=1.75mm

(wrong FB diameter, will correct in future)

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Software TestsHO Simulations

03/22/2007 HCal Electronics Meeting

Simulation Software

• Need capable and accessible simulation software option– LITRANI

• Extension of ROOT• Used for simulations in GLAST and ECAL• http://gentit.home.cern.ch/gentit/litrani/

– GEANT4, for future simulations• Slightly simpler to build simulation• Alleviates a few problems

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03/22/2007 HCal Electronics Meeting

Testing Software

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[cm]

- 1cm long, RU/RL=1, 520nm laser X-Y scan

- Aimed laser for single scattering at Z=1/2 the total length, varied reflectivity

03/22/2007 HCal Electronics Meeting

Testing Software - Mask Test

• Created mask with aperture same size as fiber diameter (0.094 cm), did X-Y scan with laser

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[cm]

03/22/2007 HCal Electronics Meeting

Testing Software - Summary

• Straight tubular LG transmits light as expected• Beam angled for a single scattering gives

efficiences ~ reflectivity• Masking of most of detector also responds as

expected• => LITRANI passes these simple tests• Results found to be symmetric with respect to

+/- and X/Y for used LG geometries

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03/22/2007 HCal Electronics Meeting

Simulations

• Simulations performed for 4 combinations of geometry and LG core– ACC = Air Core Conical LG – FC = Filled Conical LG– ACT = Air Core Trapezoidal tube LG– FT = Filled Trapezoidal tube LG

• 3 simulations run for each– E vs. Length EEfficiency– ∆E vs. Length where ∆EEcenter - Eedge

– XY Scan (really +X scan, symmetry allows)

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03/22/2007 HCal Electronics Meeting

Simulations - ACC

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-3.5mm to 2.96mm diameter taper

- Note graphs at 0.2mm

- 0.2mm => ∆E = 7.5%

03/22/2007 HCal Electronics Meeting

Simulations - FC

- Same LG filled with n=1.59 material

- 0.4cm notable compared to 0.2cm for ACC

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03/22/2007 HCal Electronics Meeting

Simulations - ACT

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- ∆E references chosen to be center and corner of LG

- E down, but ∆E also down compared to ACC

03/22/2007 HCal Electronics Meeting

Simulations - FT

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-As before, previous geometry is now filled with n= 1.59 material

-Same similarities between plots as FC

-Boost in E and decreased ∆E as in FC

03/22/2007 HCal Electronics Meeting

Simulations - XY Scans

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Zfilled=4mmZair=2mm

03/22/2007 HCal Electronics Meeting

Simulations - Summary

• ACC: E~70% ∆E~7.5% for Z=0.2cm

• FC: E~ 73% ∆E~3% for Z=0.4cm

• ACT: E~55% ∆E~5% for Z=0.2cm

• FT: E~60% ∆E~0.8% for Z=0.4cm

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03/22/2007 HCal Electronics Meeting

Results

• ~0.5cm too much scattering• < 0.2cm “masking effect”• Filling LG w/ n=1.59 boosts E allowing for

larger Z => lower ∆E • If filling LG done effectively, also protect Al

from oxidation

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03/22/2007 HCal Electronics Meeting

Results

• FC or FT => E or ∆E but ∆E diff small compared to E gain in FC geometry

• Also, trapezoidal involves more complex machining

• Research/Bench tests => Al best material

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03/22/2007 HCal Electronics Meeting

Future Work

• Bench tests at Iowa possible during late May / early June, Quarknet program

• Include QE and other effects in simulations

• Re-run simulations for correct, 2.7 mm diameter fiber bundle

• Possible to test composite LG shapes– Although, conical LG simulations were actually truncated cone

with square opening mating with SiPM

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