Polarized 3He Relaxation Studies @ Low T

N. Boccabello, D. Dutta, H. Gao, K. Kramer, X.Qian, Q. Ye, X. Zong

(Duke)L. Hannelius, B. Heyburn, R.D. McKe

own, S. Singer (Caltech)

nEDM Collaboration 2 December, 2004 Meeting

Outline

Introduction Double Cell System Improvement On the Double Cell System Results 3He relaxation time T1 due to the d-TPB

coated surface Summary & Future Plan

Introduction

Study the relaxation rate of polarized 3He under actual nEDM experimental conditions:

At Duke

1. 300 mK temperature2. enclosed in a d-TPB coated acrylic cell3. in a bath of superfluid Helium-44. at low 3He concentrations5. low B field and high E field

1. relaxation study @ 300K, 4.2K, 2.4K, 2.0K2. in the presence of d-TPB coated acrylic sticks3. with various densities of 4He

Duke Setup

Improvements On the Double Cell System

AFP loss has been reduced both in the oven cell and dewar cell

Modified Narrow Transport Tubing

Results from “Nicole”

3He density , 3He and 4He ratio ~ 1:1 With d-TPB coated surfaces 31.9% of the glass

surfaceIn the oven cell @300K In the dewar cell @ 300K

The starting points: dewar cell is better than the oven cell (~ 0.9 hr)*

cc/103.8 19

Results from “Nicole”

cc/103.8 19

)( withdTPBT

cc/100.9 193He density , 4He density 2.4K, with d-TPB coated surface @ 7G

cc/103.8 19

Comparison with Previous Measurements

[C. P. Lusher, M. F. Secca, M. G. Richards, Journal of Low Temperature Physics, V72, Nos.1/2, 1988]

Spherical sealed cell, radius~1cm, n3=3.3*1017/cc (10.1 torr), n4=7.0*1016/cc (1.99torr), nH2=5.3*1016/cc (1.51torr), @ 45KHz, 2.4K, T1 ~ 600 sec

Our double cell systemradius~2.5cmn3=8.3*1019/cc(2350 torr)

n4=9.0*1019/cc(2550 torr)

@ 34KHz, 2.4Kwith d-TPB surfaceT1 ~ 510 sec

Comparison with Previous Measurements

Ad

BAd N

NTT

3

311

TK

W

Ad

B Bem

m

A

V

N

N 3

*3

3

33

3 1

T1Ad is the relaxation time in the adsorbed phase (assume the same in two cases)

N3B is the number of 3He atoms in the bulk

N3Ad is the number of 3He atoms in the adsorbed phase

A is the effective surface area;

V is the volume of the cell

λ3 is the 3He thermal de Broglie wavelength

m3* is the effective mass of the 3He adatom

∆W3 is the adatom-substrate binding energy (~15K for 4He, and ~13K for 3He on hydrogen)sTTT doubledoubleseal 660~1.1:1: 111

The double cell system works OK!

[C. P. Lusher, M. F. Secca, M. G. Richards, Journal of Low Temperature Physics, V72, Nos.1/2, 1988]

Results from “Nicole”

Measure the relaxation times @ 300K, 4.2K, 2.4K with / without the d-TPB coated surface

Extract T1 due to the d-TPB coated surface

BwithoutdTPdTPBwithdTPB TTT

111

Results from “Nicole”

)( withdTPBT sTdTPB min3.64

)( withdTPBT

2.4K, with d-TPB surface 2.4K, without d-TPB surface

Relaxation time = 6.64 mins

Corrected R. T. = 9.82 minsRelaxation time= 8.52 mins

)( BwithoutdTPT

BwithoutdTPdTPBwithdTPB TTT

111

But the error is pretty big

sTdTPB min3.64*Due to the deterioration of the double cell system

Results from “Nicole”

T1 due to the d-TPB coated surface at various temperatures

Temp(K)B0 (G) T1 due to d-TPB (mins)

300

4.2

2.4

151.4 32.1

17.1 8.1

64.3 20.6

7

7

7

Results from “Samantha”

Contamination sources have been identified Test experiments were done to reduce the

deterioration of the cell Procedures of gas filling and pump out have

been revised to prevent contamination

Results from “Heather”

Due to accidents while chasing Rb to the pumping cell, this double cell system did not provide any useful results

The new double cell system is ready and we will be working on it soon

Summary & Future Plan

T1 due to d-TPB coated surface has been extraced for the first time @ 2.4K

More measurements are needed to reduce the error in extracting T1 due to d-TPB coated surface

Plan to carry out same measurements below lambda point

More 4He, more d-TPB coated surface will be introduced

Estimation of T1 due to d-TPB coated surface for neutron EDM cell geometry