polarized 3 he relaxation studies @ low t n. boccabello, d. dutta, h. gao, k. kramer, x.qian, q. ye,...
TRANSCRIPT
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