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W. M. Snow Physics Department Indiana University/IUCF EDM collab meeting

Monitoring the Cold Neutron Beam (During Experiment). W. M. Snow Physics Department Indiana University/IUCF EDM collab meeting. What to measure (fluence [=n/sec], polarization) How to measure (some ideas)

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W. M. Snow Physics Department Indiana University/IUCF EDM collab meeting

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  1. Monitoring the Cold Neutron Beam (During Experiment) W. M. Snow Physics Department Indiana University/IUCF EDM collab meeting What to measure (fluence [=n/sec], polarization) How to measure (some ideas) Where to measure (upstream, before cryo/cell entrance, after cell, I hope not inside the cryostat!)

  2. Parameters ~5x106 n/A/cm2/s of 9A neutrons Polarization: >95% Upstream polarizer/splitter Separate beams into ~8cm x 10 cm EDM cells Phase space @apparatus ~ 3* qc

  3. Can we monitor the beam downstream of cryostat? Even if beam/polarization can get out, 9A beams will strongly overlap in space by end of apparatus without internal guide-> at most one could measure fluence of sum of beams 2.5 m 6.4 m

  4. Measure Between end of Guide and cryo vacuum? [space, magnetic constraints] Collimator Measurement Cell Be/Teflon Multi-Foil Window at LHe/Vacuum Interface Be Foil 4°K Shield Be Foil 50°K Shield

  5. Beam Monitor Example (Various Possibilities) n+ 3He  p + t + 765 keV  ionizes gas mixture [3He +4He(~.5 atm) +N2(~.5 atm)] Works in current mode for NPDGamma Other (nonmetallic, nonmagnetic) possibility: 6Li scintillator PANIC’05 BL

  6. How can neutrons be polarized/analyzed? B gradients (Stern-Gerlach, sextupole magnets) electromagnetic F=()B B Reflection from magnetic mirror: electromagnetic+ strong f=a(strong) +/- a(EM) with | a(strong)|=| a(EM)| f+=2a, f-=0 B L  Transmission through polarized nuclei: strong ≠ -  T ≠ T Spin Filter:T=exp[-L]

  7. diode laser fiber-optic cable Polarizer cube mirror Collimating lens mirror mirror quarter-wave plate quarter-wave plate 3He Cell Dielectric mirror on 1mm thick fused silica Dielectric mirror on 1mm thick fused silica Polarized 3He Spin Filter For 9A neutrons, cell~few cm thick, P~1 atm reasonable parameters (spin exchange): on-line pumping, oven, optics,etc. or circulation (metastability exchange): flow-through system <1E-3/cm B/B uniformity required 3He cell in magnetically shielded solenoid Apparatus for on-line optical pumping

  8. Magnet Box 28 cm White Neutron Beam Plate Curvature Radius ~ 10m “Supermirror” Neutron Polarizer/Analyzer • Neutrons are polarized through • spin-dependent scattering from • magnetized mirrors • Polarization: ~98% • transmission: ~35% polarized Neutron Beam B Permanent magnet box

  9. More Compact Possibility for Polarization Analyzer? • Long wavelength cut-off filter: stack of Ni/Ti supermirrors deposited on~100 Si wafers. qc = 3* qc(Ni); qc(Ni) = 21 mrad/nm and oriented at a small angle wrt beam Supermirrors Transmitted beam [kill this with absorber] Incident beam q Reflected beam ~few cm thick In our case: eat one spin state with absorber on rear of mirror surface, use remanent polarizing SM as for incident beam polarization, but will it be nonmagnetic enough to not interfere with B requirements?

  10. Remanent Polarizing Supermirrors Exist • Retains its magnetization in a weak opposite field.

  11. Monitoring Fluence and Polarization Between Guide/Cryostat Vacuum (Do we want to do this?) Not shown: n spin transport into vac ~20 cm? Beam 1 Adiabatic Spin Flipper Upstream Cryo Vacuum q Li glass Li glass SM Analyzer Beam 2 Move IC1, IC2, SM analyzer in and out of beams horizontally Nonmagnetic enough? Reliability/Access? But measures just before entrance and no guide cut

  12. Adiabatic flipper with B gradient upstream I z r=1-sin2f/[1+k2] B x neutrons y Adiabatic parameter k=gLDB/pv>>1 Bz B L x Precession in effective field in rotating frame: w=g B2+BRF2 Rotation frequency of effective field seen by neutron: W=pv/L Adiabatic Condition:w>>W. Easy to meet for cold neutrons

  13. Monitoring Fluence and Polarization Further Upstream Similar ideas will work BUT need to cut the guide->flux loss, moving objects in vacuum,… Insert a crystal to diffract 9A beam for analysis?

  14. Ferromagnetic Shield/RF: do we have a problem with metal objects messing with RF fields? Inner Dressing Coil 50°K Shield Outer Dressing Coil 4°K Shield Gradient Coil Superconducting Lead Shield Ferromagnetic Shield B0 cosθ Magnet

  15. EDM Experiment Horiz. Section View 2 Light Guide Measurement Cell HV Generator Ground Electrode Electric Field Return HV Electrode Support

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