1. Transverse RF Spin Rotator for the n-3He experiment
Christopher Crawford
University of Kentucky
for the n-3He Collaboration
n-3He Technical Review
ORNL, TN

2. Transverse RF spin rotator
Resonant RF spin rotator
P-N Seo et al., Phys. Rev. S.T. Accel. Beam 11, (2008)
Properties suitable for n-3He expt.
Transverse horizontal RF B-field
Longitudinal or transverse flipping
No fringe field - 100% efficiency
Real, not eddy currents along outside minimizes RF leaked outside SR
Doesn’t affect neutron velocity
Compact geometry
Matched to the driver electronics of the NPDGamma spin flipper
Construction
Development in parallel with similar design for nEDM neutron guide field
Few-winding prototype built at Uky; Real RFSF being built now
NPDGamma
windings
n-3He
windings
field lines
end cap windings

3. Inner / outer coil design
Windings calculated using scalar potential
Uniform transverse RF field inside
Zero leakage field enforced by B.C.’s
Copper wires run along equipotentials
Inner region:
Intermediate:
Outer region:
4:1 inside / outside winding ratio
By choosing appropriate radii
Perfect cos theta windings inside & out
48 inner loops of 18 AWG wire

4. Status
Waiting for winding grooves to be machined in nylon forms

5. Alternate winding patterns
Three possibilities all give same field in high-frequency limit INNER INNER/OUTER OUTER
easiest to wind no eddy currents no copper in beam
All three wound using same grooves
R&D: test RF fields of each winding

6. Electrical specifications
Holding field:
Resonant frequency:
Inductance: 4.5 mH
Capacitance: 7.5 nF
Resistance: 5.1 Ω
Maximum voltage:
Stored energy:
Dissipated power:
Quality factor: Q=151

7. Electrical specifications
RF field strength depends time spent in RFSF.
High energy neutron beams (~20 meV) will be travelling upwards of 1000 m/s
These neutrons will spend approximately 398 microseconds inside the RFSF and need to rotate π-radians
Flip rate:
The maximum value of the required rotational field is then,
The maximum value of the required RF field is exactly twice this,
To produce this field, we calculate the maximum value of required current given the winding spacing of the inner coils.
Proportionally Constant: