R&D Plan on Light Collection

1. R&D Plan on Light Collection Takeyasu Ito Los Alamos National Laboratory

2. Light Guides and PMT’s • Requirements—20 p.e. per event (for particle ID) Schematic of light collection / detection conv: conversion efficiency Atrap: trapping efficiency pmt: quantum efficiency trans: transport efficiency PMT One or more thermal break(s) Neuv TPB coating tpb:Solid angle subtended by the TPB coating at the location of the 3He+n reaction LHe

3. 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 (~0.17 ) • trans : efficiency of the light transport in the light guide • pmt : quantum efficiency of the photocathode of the PMT (~0.15 )

4. A Possible Geometry • Extracting light from both edges of the side walls • Need trans > 60% • Operate PMTs at 4K to reduce loss due to thermal breaks (R&D underway)

5. Questions that need to be answered by the R&D • Can we get Neuv > 20 (or trans > 60%) in the geometry that can be used in the EDM experiment? • How does the EUV scintillation light yield (for both prompt and afterpulse) change with the electric field? • What is fprompt for p and t from neutron capture on 3He?

6. Test #1 • Purpose: • Measure (geometry dependent factors) • Note: • Map the position dependence • Method: • Build a full scale mock-up/prototype of the measurement cell + light guide system • Fill the cell with Ar gas and use the 128nm scintillation light caused in the Ar gas by  particles • Measure the number of p.e.’s and compare it to that obtained from a more simple known geometry (control experiment)

7. Test #1 schematic Measurement cell ~1.2 m 2” tubes (upto12) ~0.6 m Light guide  source(s) Ar gas Light tight, gas tight box

8. A few remarks on Test #1 • The energy deposition necessary to create one 128 nm photon in Ar is 67.9 eV. • In principle, we know Neuv for  in Ar, but not conv. Therefore we need the control experiment, which determines Neuvconv. • ’s mean range is 3-4cm in 1atm Ar gas (for 241Am). • Need MC to calculate tpb to interpret the control experiment. • The photon yield is very sensitive to the contamination in Ar gas.

9. Test #2 • Purpose: see if the liquid helium scintillation light yield (both prompt and afterpulse) changes with the electric field • Method: • Stick light guide between the electrodes in the HV test apparatus • The front face of the light guide is coated with TPB • Place  (and  source(s) in front of the front face of the light guide • Measure the light yield as a function of the applied electric field • By keeping the electrode separation small (up to ~2cm), it is possible to generate a high electric field.

10. Test #2 schematic  or  source Light guide (Acrylic rod with rounded off edge) LHe 0.3-0.5K PMT existing10” port TPB coated surface

11. Test #2 schematic PMT housed in vacuum

12. Budget

13. Test #1 Schedule

14. Test #2 Schedule