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

Neutron EDM: Polarized 3 He D. Beck, UIUC LANL Apr 03 Outline 1. Context 2. Relaxation studies 3. Source development

Polarized 3 He: Context • Role of 3 He in experiment 1. Measure spin precession of neutrons - detect scintillation of p, t from capture reaction 2. Measure (local) magnetic field - detect 3 He precession frequency with SQUID P 3 = P n = 1.0 • Require high 3 He polarization P 3 = 0.5, P n = 1.0 - maintain P 3 > 95% to minimize P 3 , P n = 0.5 500 impact on final uncertainty Φ Scint (Hz) 400 300 200 100 20 40 60 80 100 t (s) DHB, NSAC Neutron Review, 17 Apr 03

3 He in L 4 He • Important first step: measurements using n + 3 He → p + t at LANCSE • See uniform distribution of 3 He in L 4 He - Hayden, et al., Physica B , in press • Important first step for relaxation of 3 He pol’n (P 3 ): measurement of diffusion coefficient - Lamoreaux, et al., Europhys. Lett. 58 (02) 718 - D ~ T -7 below 0.7 K DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: Relaxation • To maintain high polarization require long relaxation times - “longitudinal”, T 1 (decay of P 3 ) Need ~10 4 s - “transverse”, T 2 (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: T 1 = 4x10 5 s for - X 3 = 7x10 -4 , T = 4.2 K, B = 3 mG, r = 1 cm Pyrex, solid H 2 coating • Transverse relaxation time - important contribution from diffusion in field gradient - in this case, depends on absolute gradient G i = dB/dx i DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: Relaxation Studies Duke/Caltech/ . . . • Measure relaxation times in range 2 – 4 K - “spin exchange” optical pumping to polarize 3 He - pumping of alkali in 440 K cell - glass, acrylic system - NMR detection of precessing 3 He spins - requires larger X 3 • Manpower - Dutta, Gao, Ye (g.s.) + 1 u.g. - McKeown, Hannelius (g.s.), Singler (u.g.) DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: Relaxation Studies Duke/Caltech/ . . . Helmholtz coils for holding field Diode laser for pumping alkali (Gao, Duke) (Gao, Duke) DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: Relaxation Studies UIUC/Duke/Caltech/ . . . • At UIUC, extend initial measurements at Duke - lower temperatures - smaller concentrations X 3 - perhaps SQUID detection cryostat - ultimate goal to duplicate target cell conditions as insert closely as possible • Perhaps incorporate LANL 3 He ABS • Developing multi-purpose test facility expt. - T ≥ 0.3 K by pumping L 3 He space - ½ scale neutron target cells - ¼ scale magnet, shields Test system at UIUC DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: Relaxation Studies UIUC/Duke/Caltech/ . . . • Instrumentation cryostat - thermometry to < 0.3 K - cryogenic Hall probe • Manpower cryostat - Beck, Williamson, Hubler (u.g.), insert Kenyon, Thorsland (tech) experiment space Test system at UIUC DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: 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 L 3 He - 1.25 m long quadrupole cryogenic 3 He source quadrupole state selector Assembled 0.7 K nozzle at LANL DHB, NSAC Neutron Review, 17 Apr 03

Polarized 3 He: Source • Simulated performance - P 3 > 99% - I 3 > 10 14 s -1 • Test - build two quadrupole sections - r.f. spin flip in-between - use second section as analyzer • Manpower - Lamoreaux, Torgerson, Boissevain Assembled spin selection quadrupole at LANL DHB, NSAC Neutron Review, 17 Apr 03

Neutron EDM: Polarized 3 He Summary 1. Polarized 3 He 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) DHB, NSAC Neutron Review, 17 Apr 03