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 2013-01-08

Transverse RF spin rotator Resonant RF spin rotator P-N Seo et al., Phys. Rev. S.T. Accel. Beam 11, 084701 (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

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

Status Waiting for winding grooves to be machined in nylon forms

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

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

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: