Neutron Electric Dipole Moment

1. D. Beck (Intro)2. S. Williamson (He3 Services construction and testing)3. L. Yang (Light collection)

with J. Blackburn, J. Nicholson, T. Rao, S. Sharma, P. Sobel, E. Thorsland

nEDM@SNS Status Ongoing development project Currently in year 2(of 4) of “Critical

Component Demonstration” phase Successful completion of Critical

R&D phase in Dec. 2013 Continued Annual Reviews,

Technical Review Committee meetings

15 critical component activities GOAL: reduce risk, build from

inside out

Equipment funding from NSF for He3 Services (UIUC), Magnet Systems (Caltech) at ~$1.4M/year

Equipment funding from DOE for Central Detector System, Cryogenics, Neutronics at ~$1.8M/year

Lessons learned modified design

He3 services

Central Detector

2

Measure neutron precession frequency in NMR-style experiment

Experiment OverviewConcept: Golub and Lamoreaux, Phys. Rep. 237 (1994) 1

Measurement cell cutaway

HV

Ground

MeasurementCells (7.6x10x40 cm)

BE

n

n

Scintillation signal (B/40)

h=2(BdE)

• (n + 3He) ~ 0, (n + 3He) ~ 2 Mbarns 3He co-magnetometer

3

Experiment Statistics

Incident neutron fluence cold ~ 3x108 n/s: ~ 0.3 Å FWHM

UCN density at beginning of measurement

nUCN ~ 100 cm-3

Polarized 3He density n3 ~ 1012 cm-3, n3/n4 ~ 5x10-11

Cell volume x·y·z = 7.6·10·40 cm3 = 3100 cm3

Holding field B0 ~ 30 mG x

Electric field E0 ~ 50 kV/cm x

Precession frequencies fn ~ 100 Hz, |fn – f3| ~ 9 Hz

Operating temperature Top = 0.45 K

Refrigeration ~80 mW @ 0.25 K

Official sensitivity (3 years) d = 3-5x10-28 e·cm (90% CL)

4

nEDM Activities

UIUC responsible for “3He Systems” Getting the polarized 3He both in and

out

• Source is existing Atomic Beam Source

• Use “heat flush” to remove(3He transported using phonons)

3He enters some distance from measurement cells plumbing including valves, etc.

He3 Services Critical Component Demonstration activities (Williamson) Dilution Refrigerator Injection System Purification System

WLS fiber light system readout (Yang)

Atomic Beam Source

to Central Detector

He3 Services System

Dilution Refrigerator

Injection system

Purification system

5

nEDM Activities in Support (DHB)

1. Theory of transport coefficients of dilute solutions of 3He in superfluid 4He (heat flush)

Baym, Beck and Pethick Phys. Rev. B 88, (2013) 014512; JLTP 178 (2015) 200, and to be published

2. Design and performance of magnetic shielding for nEDM experiments (with TUM)

I. Altarev, et al. Rev. Sci. Instrum. 85 , 075106 (2014)

3. Possible test nEDM experiment at ILL (Illinois student?) CryoEDM cancelled at ILL

4. Development of external atomic vapor magnetometry for TUM experiment1. Require array of magnetometers

2. Proof of principle of all-optical vector magnetometry (B. Patton, et al. PRL 113 (2014) 013001)

l Development of cryogenic NV-diamond magnetic and electric field sensor STTR DE-SC0011266 with Southwest Sciences & Sarvagya Sharma

6

Introduction

Injection system

Film-burner test

The InjVol/IV1 conductance test

Radiation heat-load test

Purification system

Heat-flush test

Dilution refrigerator

Steve Williamson

nEDM@SNSHelium-3 Services

7

Polarized 3He in nEDM@SNS

The experiment relies on efficient…

injection of polarized 3He into isotopically purified 4He

transport of the polarized 3He to the measurement volumes

maintenance of polarization during the measurement

removal of unpolarized 3He when a precession measurement is complete.

Inject3He and n

Move 3He to Measurement

Cell

Measure

Remove Unpolarized

3He

8

Where are we? Critical Component Demonstration (CCD)

A working dilution refrigerator meeting the nEDM@SNS operational

and material requirements

Critical components for the injection and purification systems

individually tested at operating temperature

All testing, including full He3 services cryostat, at UIUC

2014

Pre FY12Pre FY12 Critical Component DemonstrationCritical Component Demonstration

Large Scale IntegrationLarge Scale Integration

Conventional ComponentsConventional Components

2012 2018 2021

R&DR&DData Collection

Assembly and Commissioning …

Helium-3 Services (He3S) CCD Goals

9

Injection SystemABS

Film-burner

InjVol

IV1

InjVol valve

Prepares polarized 3He in isotopically purified 4He for transport to the measurement cells.

Some of the CCD challenges :

Control superfluid film from bulk LHe in InjVol.

Cooling InjVol and IV1

• Plastic (no metal), no sinter

• InjVol is coldest point in He3S (300 mK)

• IV1 must come to equilibrium quickly

Thermal isolation and seal of InjVol valve

10

Evaporation of film into beam line must be prevented Produces large heat load to injection volume

(HeVAC)

4He gas can block the beam (3He-4He atomic scattering)

Film-burner concept Evaporate the film with a heater.

Then re-condense it where …• cooling is efficient and

• gas conductance to beam line is low

Film-burner Heater

Injection Volume

LHe, T= 0.3 K

Film-burner Assembly

Baffle

Bea

m li

ne f

rom

A

tom

ic B

eam

Sou

rce

To IV1 and the rest of the experiment

Superfluid Film Control

11

Detect film (or its absence) to measure

required heater power

Measure atomic “beam” transmission to be

sure vapor is trapped.

Superfluid Film Control Test

Film-burner Heater

Upper film sensor (dry if FB works)

The

rmal

Lin

k

Therm

al Link

Dilution Refrigerator Mixing Chamber

NTD Ge Bolometer

LHe, T= 0.3 K

Source ROX

Injection volume assembly

Film-burner Top flange assembly

12

Detect film (or its absence) to measure

required heater power

Measure atomic “beam” transmission to be

sure vapor is trapped.

Superfluid Film Control Test

Injection volume assembly

Film-burner Top flange assembly

Mixing chamber of Silvera DR (Harvard)

Film-burner assembly

Injection volume

assembly

Top flange assembly

13

Transmission at 0.310 K

14

Transmission at 0.310 K

15

The InjVol/IV1 Conductance Test

The results: Slope of each T vs P curve is

thermal resistivity

Extrapolates, for real geometry, to ~0.9 mW at Tfridge = 250 mK

But what will the actual heat load be?

Stainless outer wall

Top flange bolted to MC

19.3 mm OD, 77 µm wall Kapton

inner wall

Heater bobbin

LHe here

LHe here

Silver sinter

~11 cm

Bottom flange assembly showing Kapton tube0.0 0.2 0.4 0.6 0.8 1.0

0

20

40

60

80

200mK outside 220mK outside 250mK outside 275mK outside 300mK outside

delta

T in

side

(m

K)

inside heater power (mW)

change in inside temperature vs inside heater powerT vs. Inside Heater Power

The problem: Plastic injection volume (InjVol) and IV1 must be

cooled to 0.3 K. No metal or sinter allowed on InjVol What is the maximum power that can be removed

through the walls?

The test: Double-walled volume; LHe thermal link to DR. Temperature sensors in both volumes Inner wall of seamless Kapton tubing Heat inner volume Measure T vs heater power

16

Radiation Heat Load Test

Most of the InjVol heat load is from 300 K thermal radiation

Estimate is too uncertain COMSOL FEA: 0.066 mW

Ray-trace: 0.42 mW

A test would be prudent: Simple geometry, an “upper limit” for the beam line.

1. Pull copper plug to 300K.

2. Measure absorber temperature (with radiation).

3. Push copper plug to thermally connect at 4.2K.

4. Adjust absorber heater to obtain the temperature of step 2.

Results First test at ~15K 0.45 mW for the real geometry.

More analysis of this test is necessary.

Repeat test at lower temperature.

~115 cm

Absorber

Copper plug

Radiation test insert (for standard LHe storage dewar)

17

Purification System

Removes depolarized 3He from measurement

cells; provides isotopically pure 4He

CCD activities:

Heat-flush test• New capacitor (3He density sensor) design to be

tested in early 2015

Adjustable Thermal Link (ATL)• With greater DR cooling power, may be

unnecessary

• Analysis in progress

Sequestration Volume (SV)• Is 3He dumped with bulk 4He? test

SV

ATLs

18

The Heat-flush Test The concept:

Measure heat flush on “reasonably large” scale

Compare to theory (Baym, Beck, and Pethick)

Apply theory to the “real experiment” design

The test: Use osmotic pressure to measure X100 concentration

change

• For natural He, 0.45K, X100 concentration change,ΔP = 10-3 Torr

Capacitive pressure sensor• 0.5” diameter 25m-thick Kapton

diaphragm deflects by 0.57 m

• With 25m gap, capacitance changes from 44.16 to 44.49 pF (0.77%)

3 BP n k T

Heat-flush test assemblySection view of capacitive pressure sensor

Solid electrode (diaphragm not visible on this scale)

Superleak (not shown)

19

Dilution Refrigerator Some characteristics

Magnetic field gradient specs only non-magnetic materials allowed.

Close coupling with He3S

Hybrid operation as 3He evaporation fridge

Optimized to run at 85 mW of cooling power (30% reserve) at ~200 mK

Ultimately 2 DRs are needed (one for He3S, one for CDS)

Build first DR for He3S DR test bed at UIUC “barn”

• Space for large equipment

• LHe from UIUC Physics liquefier

• Helium recovery infrastructure

• Close to NPL technical support

DR will be critical to He3S component testing during last year of CCD CAD Model of the DR Test Stand setup in the

NPL High Bay Area20

Dilution Refrigerator CCD Activities

DR test-bed, 3He gas panel, slow control, cryostat, helium supply

Dewar and transfer line, He gas recovery, DR “Insert”

Substantial amount of commercial purchasing complete

Cryostat leak checked, fabrication tasks beginning

Low-temperature 3He circulation components (the still, mixing

chamber, heat exchangers, impedances)

Technically challenging multiple prototypes

Testing

The DR test-stand setup begins to take shape in the High Bay Area 21

In the next 3 years…

A working dilution refrigerator meeting the nEDM@SNS operational

and material requirements

Used during last year for He3S component testing

Critical components for the injection and purification systems

individually tested at operating temperature

Focus on most uncertain components first

The rest of the parts and assembly-level testing in the post-CCD phase

22

Measuring Neutron Precession using Helium Scintillation

• Neutron precesses at a slight different frequency than 3He, ~ 10%.

• Neutron absorption on 3He is highly spin dependent. Reaction products of n+3He→p+T generates UV scintillation (80 nm) in LHe.

• The UV photons are down-converted before detection.

• Spin dependent n - 3He absorption reaction measures the difference in precession frequencies between neutron and 3He.

L. Yang, UIUC

23

nEDM Light Collection R&D

Optimize the light collection using simulation given other system constraints on HV, magnetic field, neutron activation, etc.

Demonstrate the efficiency of the photon detection system with a full scale prototype.

An early conceptual design of light collection system

24

Full Scale Test Apparatus

• A full scale prototype was constructed at ORNL to test light collection

• Detection efficiency of 80 nm scintillation light significantly lower than expected.

• Collection of UV photons from LED agree with expectation.

• Suspect that some down-converted blue photons are not trapped in the cell wall.

25

Alternative Detection Scheme

• Adding wavelength shifting fibers at the outside the cell wall significantly increased the light detection efficiency.

• Supports the model of reduced optical capture efficiency for blue photons.

26

Light Collection Simulation

Light Guide, PMTs

WLS fiber, SiPMs

• UIUC and Miss. State are collaborating on the development of GEANT4 simulation of the light collection.

• Use the experimental data and simulation to better understand the UV photon down-conversion process and light propagation.

• In the process of determining unknown parameters.

27

SiPM Testing

• Silicon photomultipliers (SiPMs) offer better quantum efficiency and distinct P.E. peaks.

• KETEK evaluation package stopped working at 110 K. • UIUC is developing a front end readout package.

KETEK SiPMPreamp Box

Synergy with nEXO readout electronics R&D (Yang) and sPHENIX EMCal detector R&D (Sickles).

28

Future Light Collection R&D at UIUC

• Refine the light simulation and optimize WLS fiber readout.

– Improve detector energy resolution to reduce background events from beta decay and environmental gammas.

– Develop position reconstruction capability with fiber readout, a new handle on background reduction and systematics studies.

• Develop full scale readout with SiPMs

– Low noise front end readout

– Mechanical and thermal design for the SiPM system

– Upgrade the DAQ to handle a large number of channels.

29

nEDM Summary

In demonstration/construction phase “CCD” Strategy is still “design-build-test”, repeat as necessary Build internal (less expensive) components first; beamline, large

cryostats, magnetic shielding, infrastructure (more expensive) later

UIUC responsible for 1.He3 services: getting polarized 3He to measurement cells, removing

(de-)polarized 3He

• Dilution refrigerator construction

• Injection volume prototype (film burner, vessel, radiation heat load): @Harvard

• Heat flush test (demonstrate feasibility, compare to theory) @Harvard

• Need for postdoc to help manage and execute parallel activities

2.Fiberized light collection development (with ORNL, Miss. State)

• Synergy with development for nEXO30