# Presentation: 686574

## Light Guides and PMT’s (from T. Ito slides, Pasadena, Feb 2007)

- Light Guides and PMT’s (from T. Ito slides, Pasadena, Feb 2007)

- LHe

*N**euv*

- TPB coating
- *tpb*:Solid angle subtended
- by the TPB coating at the
- location of the 3He+n reaction

***conv*: conversion efficiency

*A**trap*: trapping efficiency

***trans*: transport efficiency

***pmt*: quantum efficiency

- PMT

- One or more thermal break(s)

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

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Light collection simulation

- From T. Ito’s slide 3
- (Pasadena, Feb 2007)

- Summary of results from litrani (details to follow):

- (with 1 thermal break)

- (assumes perfect surfaces)

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Acceptance of UV light on Cell walls

- Where does the UV light go, as a function of (x,y,z)
- of generation point?

-  For -15 cm < z < 15 cm, side walls see 90% of the light
-  When opposite walls summed, light collection does not depend much on (x,y) location

- 50 cm

- 10 cm

- 10 cm

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Adiabatic Guides attached to lucite cell

- downstream

- upstream

- 100K photons (400 nm) generated into 2** **from surface of sidewall
- downstream
- accepted = 14631
- upstream
- accepted = 10414
**total = 25%**

- Josh Rehak, U Md 1/22/2008

- if perfect optical coupling between guide and detector

- bend radius
- = 15 cm

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Adiabatic Guides attached to lucite cell

- downstream

- upstream

- 100K photons (400 nm) generated into 2 from surface of sidewall
- downstream
- accepted = 8694
- upstream
- accepted = 6832
**total = 15.5%**
**	**

- Josh Rehak, U Md /22/2008

- with (1 m) air gap between detector and guide

- bend radius
- = 15 cm

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Rectangular Guides vs Adiabatic Guides

- >300 shapes per adiabatic guide
- Very complicated to rotate into place
- in simulation
- Use much simpler rectangular guides
- for majority of tests and then scale

- 100K photons generated (**uniformly into 4******) along a single wall
- no other side walls are in optical contact, no endcaps

| 100K thrown | upstream (200 cm) | downstream (100 cm) |
| --- | --- | --- |
| rectangular | 6744 | 8581 |
| adiabatic | 6700 | 8662 |

- (w/ air gap between guide & det)

- bend radius = 15 cm

- bulk absorption length = 450 cm

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## How much is lost in endcaps?

- For side walls = 50 cm,  (lucite) endcaps = 1.27 cm and optically coupled to side walls (but no emission from ends)
-  15% reduction in accepted light

- detector

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Where does the (blue) light go?

- 100K photons generated along each wall (400K total)

- (1) lucite side walls (1.27 cm) in optical contact, lucite endcaps optically connected to side walls.   A single pair of (rectangular) guides sees (with air gap between guide and detectors)
- 		7600 photons from own wall
- 		2400 from each adjacent wall
- 		1000 from opposite wall										= 3.3% total
- 		(also, 3% lost into the two endcaps)
- (2) 8 lightguides, *** total collected = 13.5%**	**(3.3% per detector pair)*
*	**(no losses/bounce or surface roughness yet included)*
*	**	*

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Estimated Surface Losses (H.Breuer)

- Cast surface absorption:  .. 0.2%
- Machined surface abs.: .... 2.0%
- Bulk attenuation length:  450 cm
- Reflections:
-    0-100 cm: every 1.5 thickness
-    100-200 cm: every 2.2 thickn.
- Light guides:
-  - 1⁄4 inch thick
-  - 2 strips  2.5 cm wide
-  - 4 strips  5.0 cm wide
- Coated wall:
-  10cm x 50 cm, one piece

- Reflection survival:
-   100 cm guide:            0.55
-   200 cm guide:            0.39
-   100+200 guide:                  0.47
- (100+200 bulk attenuation:  0.60
-   already included in earlier slides)
- Components of attenuation:
-             guide (cm):    100     200
- - Cast surfaces:        0.81    0.74
- - 2.5 cm machined:   0.58    0.41
- - 5.0 cm machined:   0.76    0.64

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008

## Losses: 1 vs. 2 light guides (H.Breuer)

- 2 light guides (100 + 200 cm) survival:         0.330 {0.231}
- 1 light guide (100 cm + reflector) survival:    0.378 {0.328}
- ... 15% overall improvement {42% for replaced 200cm} due to
-             shorter path  length
-             much fewer surface reflections
- Using:
- 100 cm light guide + (100 cm +50 cm wall piece)
- 5% reflector loss
- Assuming wavelength shifter coating acts like a cast surface (99.8 reflectivity, very iffy!)
- Needs MC and test verification.

- E. Beise, U Md

- ASU  nEDM mtg, Feb 2008