Dressed spin studies with polarized 3 he
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Dressed Spin Studies with Polarized 3 He. Andrea Esler & Jen-Chieh Peng (UIUC). Steve Lamoreaux & Chen-Yu Liu (LANL). Dressed Spin. Strong RF fields change the effective magnetic moments of neutrons and 3He First 3He spin dressing measurements performed in April 2005

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Dressed Spin Studies with Polarized 3 He

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Dressed Spin Studies with Polarized 3He

Andrea Esler & Jen-Chieh Peng (UIUC)

Steve Lamoreaux & Chen-Yu Liu (LANL)

Dressed Spin

Strong RF fields change the effective magnetic moments of neutrons and 3He

  • First 3He spin dressing measurements performed in April 2005

  • Change of 3He Larmor frequency with a dressing field has been observed.

In the B0<<B1 limit, the g factor modification has a simple formula

Effective g factor vs. RF field strength:

Dressed Neutron Spin already observed

Muskat, PRL 58(20), 1987

Numerical simulations reproduced these results

Fits the J0(gB1/w) prediction

Critical dressing equalizes precession rates

  • Reduce the effect of B0 [instability] on the two species

  • A check of gn=g3: scintillation no longer modulated

Crossing points equalize neutron and 3He g factors:

Effective dressed g factors:



Polarized 3He Source

Spin flip region



Injection nozzle



1 K cold head



4 m


Solenoid field 8 Gauss

3He detector


Spin polarizer

Spin analyzer


90 cm

Adding an RF dressing field slows down spin precession between the flip coils (or speeds it up…) & changes the minimum transmission frequency

Ramsey experiment technique (SOF)

Images courtesy Sussex Neutron EDM group

Free precession

Incoming 3He

p/2 pulse

Second p/2 pulse


Z component of nuclear spin

Analyzer & Counter


accepts P=+1 state

When the RF pulses are applied on resonance (at the Larmor frequency) the 3He spin direction is completely reversed (minimal transmission)

3He experiment setup

Ramsey coils and dressing coils are inside the solenoid



to analyzer and RGA detector


3He beam polarization: P > 95%

Unpolarized transmission

Full beam transmission

RGA pressure reading

” p pulse” field setting

Spin-flip magnetic field B1 x distance

Dec. 2004: P=99.6% was measured with better shielding

From Dec. 2004 meeting:

1 K “Maxwell” dist.

Accepted velocities

Img. courtesy S. Lamoreaux

  • Polarization (as fn. of B1) averages over 3He velocities

  • P(B1) measures Fourier cosine transform of velocity spectrum

  • Invert the FT to measure N(v):

Velocity spectrum deduced from April measurements needs to be calibrated, but we expect agreement

3He beam background pressure

open and closed shutter

6 nTorr

the same, log scale

0.01 nTorr

Mapping the dressing field

Dressing magnet coil

Dressing coil field map

Average field: 1.6 Gauss / Ampere

3He dressed spin results I

Dressing field frequency 43.5 kHz

Increasing dressing field

Minimal transmission rate observed at the 3He Larmor precession frequency

3He Larmor Freq. Dressed at 43.5 kHz

Max B field

5.8 G

Inconsistent with simple formula; B0~B1

43.5 kHz data vs. simulation

Rough agreement with Bloch-equation simulations

– I am working to refine the code

3He dressed spin results II

Dressing field frequency 8.1 kHz

Increasing dressing field

3He Larmor Freq. Dressed at 8.1 kHz

Max B field

1.6 G


  • Continue analysis

    • Understand observed Larmor freq. behavior

  • Upcoming measurements (this week) will emulate EDM experimental conditions

    • More intense dressing fields over smaller volume (new coils already built)

    • Smaller B0 (limited by earth’s field ~5 G)

    • Larger dressing field frequency ~50-100 kHz

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