Neutron EDM: Polarized 3 He D. Beck, UIUC LANL Apr 03 Outline 1. - - PowerPoint PPT Presentation

Neutron EDM: Polarized 3He

• D. Beck, UIUC

LANL Apr 03

Outline

• 1. Context
• 2. Relaxation studies
• 3. Source development

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Context

• Role of 3He in experiment
• 1. Measure spin precession of neutrons
• detect scintillation of p, t from capture reaction
• 2. Measure (local) magnetic field
• detect 3He precession frequency with SQUID
• Require high 3He polarization
• maintain P3 > 95% to minimize

impact on final uncertainty

20 40 60 80 100 100 200 300 400 500

ΦScint (Hz) t (s) P3 = Pn = 1.0 P3 = 0.5, Pn = 1.0 P3, Pn = 0.5

DHB, NSAC Neutron Review, 17 Apr 03

3He in L4He

• Important first step for relaxation of

3He pol’n (P3): measurement of

diffusion coefficient

• Lamoreaux, et al.,
• Europhys. Lett. 58 (02) 718
• D ~ T-7 below 0.7 K
• Important first step: measurements using n + 3He → p + t

at LANCSE

• See uniform distribution of 3He in

L4He

• Hayden, et al., Physica B, in press

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Relaxation

• To maintain high polarization require long relaxation times
• “longitudinal”, T1 (decay of P3)
• “transverse”, T2 (decay of signal after π/2 pulse)
• contributions from wall interactions, diffusion in field gradients
• Longitudinal relaxation
• relative field gradients enter

G/B = d(logB)/dx

• measured value in most similar case:

T1 = 4x105 s for

• X3 = 7x10-4, T = 4.2 K, B = 3 mG,

r = 1 cm Pyrex, solid H2 coating

Need ~104 s

• Transverse relaxation time
• important contribution from

diffusion in field gradient

• in this case, depends on absolute

gradient Gi = dB/dxi

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Relaxation Studies Duke/Caltech/ . . .

• Measure relaxation times in

range 2 – 4 K

• “spin exchange” optical

pumping to polarize 3He

• pumping of alkali in 440 K cell
• glass, acrylic system
• NMR detection of precessing

3He spins

• requires larger X3
• Manpower
• Dutta, Gao, Ye (g.s.) + 1 u.g.
• McKeown, Hannelius (g.s.), Singler

(u.g.)

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Relaxation Studies Duke/Caltech/ . . .

Helmholtz coils for holding field (Gao, Duke) Diode laser for pumping alkali (Gao, Duke)

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Relaxation Studies UIUC/Duke/Caltech/ . . .

• At UIUC, extend initial measurements at Duke
• lower temperatures
• smaller concentrations X3
• perhaps SQUID detection
• ultimate goal to duplicate target cell conditions as

closely as possible

• Perhaps incorporate LANL 3He ABS
• Developing multi-purpose test facility
• T ≥ 0.3 K by pumping L3He
• ½ scale neutron target cells
• ¼ scale magnet, shields

Test system at UIUC cryostat insert expt. space

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Relaxation Studies UIUC/Duke/Caltech/ . . .

• Instrumentation
• thermometry to < 0.3 K
• cryogenic Hall probe
• Manpower
• Beck, Williamson, Hubler (u.g.),

Kenyon, Thorsland (tech)

Test system at UIUC cryostat cryostat insert experiment space

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Source

• Simple quadrupole atomic beam source (ABS) design
• should provide
• very high polarization
• modest (more than sufficient) flux
• overcome limitations of small nuclear

moment – long dwell time

• nozzle cooled by pumping L3He
• 1.25 m long quadrupole

Assembled 0.7 K nozzle at LANL quadrupole state selector cryogenic 3He source

DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3He: Source

Assembled spin selection quadrupole at LANL

• Simulated performance
• P3 > 99%
• I3 > 1014 s-1
• Test
• build two quadrupole sections
• r.f. spin flip in-between
• use second section as

analyzer

• Manpower
• Lamoreaux, Torgerson,

Boissevain

DHB, NSAC Neutron Review, 17 Apr 03

Neutron EDM: Polarized 3He

Summary

• 1. Polarized 3He used
• to measure neutron precession rate via capture reaction
• to measure local magnetic field
• 2. Relaxation studies
• present measurements set bounds on field gradients
• measure wall relaxation
• two stages: T > 2 K (Duke), T < 2 K (UIUC)
• 3. Source development
• beginning tests of high polarization atomic beam source (LANL)