Powdered TPBvs

TPB Embedded in Plastic Matrix

Takeyasu ItoLos Alamos National Laboratory

EDM Collaboration MeetingPasadena, Feb 14-15

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Light Guides and PMT’s

LHe

Neuv TPB coatingtpb:Solid angle subtendedby the TPB coating at thelocation of the 3He+n reaction

conv: conversion efficiency

Atrap: trapping efficiency

trans: transport efficiency

pmt: quantum efficiency

PMT

One or more thermal break(s)

Schematic of light collection / detection

• Requirements—20 p.e. per event (for particle ID)

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Number of Photoelectrons

• Npe: number of photoelectrons

• Neuv: number of extreme ultraviolet photons– Neuv = Edeposit fprompt / eeuv

– Edeposit = 760keV; eeuv = 16 eV– fprompt = 35% for , 9% for when E=0 kV/cm p, t should be somewhere in between– Using fprompt=9% gives Neuv = 4.3x103 euv photons

• tpb: solid angle subtended by the TPB coating at the location of the n+3He capture event

• conv: conversion efficiency of TPB (~0.3 for TPB in plastic matrix)

• Atrap: fraction of the visible photons that meet the condition for the transmission by total internal reflection in the light guide (~0.34-0.50 if readout from both edges )

• trans : efficiency of the light transport in the light guide

• pmt : quantum efficiency of the photocathode of the PMT (~0.15 )

€

N pe = NeuvΩ tpb

4πεconvAtrapε transε pmt

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• Extracting light from both edges of the side walls

• Need trans > 30%

• Operate PMTs at 4K to reduce loss due to thermal breaks (R&D underway)

A Possible Geometry (current baseline)

€

N pe ≈ 66 ×Ω tpb

4πε trans

≈ 66 ×ε trans

(for events that occur

near the center of the cell)

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Powder TPB vs TPB embedded in plastic matrix

LHe

Neuv

conv ~ 1

LHe

Neuv

conv ~ 0.3

Note: Powder TPB only possible for the top and bottom walls.

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Trapping fraction — readout from the ends

€

f trap =1− 4 ×2π sinθdθ

0

θ c∫4π

= 49.8%

Light source

Light that emitted into these cones is lost(There are two more cones coming out to the side walls that are not shown.)

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Trapping fraction — tube

€

f trap = 2 ×2π sinθdθ

0

π / 2−θ c∫4π

= 33.8%

c

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Trapping fraction — light source outside the light guide

c=41.5˚(n=1.508)

€

f trap =2π T(θ)sinθdθ

0

π / 2

∫4π

≈ 40%

c

T()

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Fresnel’s equation

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Powder TPB vs TPB in Plastic Matrix

Powder TPB TPB in Plastic Matrix

conv 1 0.3

ftrap 40% 35-50%

Area to be covered by PMTs (bottom and top only)

2032 cm2 103.2 cm2

# of 2” PMT’s 114 18

# of P.E.s ~123 x trans ~ 66 x trans

Remarks:•TPB in plastic matrix might give us enough PE.s depending on trans

•If that is the case, TPB in plastic matrix is more advantageous because of the smaller number of necessary PMTs•Both should be tested in the mockup, and also both should be modeled/simulated.

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Light guide test box

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Trapping fraction x transmission efficiency

Light source

3 in. .5 in.

1.25 m

€

f trapε trans =transmitted

generated= 26%

Assuming 1% loss per bounce

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Trapping fraction x transmission efficiency

Light source

1 cm 1 cm

1.25 m

€

f trapε trans =transmitted

generated=14.5%

Assuming 1% loss per bounce

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Trapping fraction x transmission efficiency

Light source

0.3 cm0.3 cm

1.25 m

€

f trapε trans =transmitted

generated= 2.9%

Assuming 1% loss per bounce