A High-frequency, Low-power Resonant Radio-frequency Neutron Spin Flipper for High-resolution Spectroscopy

TL;DR

This paper introduces a superconducting rf neutron spin flipper that achieves high efficiency at 4 MHz for high-resolution spectroscopy, with potential for further improvements in frequency and performance.

Contribution

The paper presents a novel superconducting rf neutron spin flipper design that combines high efficiency and high frequency operation for neutron spectroscopy.

Findings

Achieved 96.6% neutron spin-flip efficiency at 4 MHz

Demonstrated high-resolution spectroscopy capabilities

Identified magnetic field homogeneity as a key limitation

Abstract

We present a resonant-mode, transverse-field, radio-frequency (rf) neutron spin flipper design that uses high-temperature superconducting films to ensure sharp transitions between uniform magnetic field regions. Resonant mode allows for low power, high frequency operation but requires strict homogeneity of the magnetic fields inside the device. This design was found to efficiently flip neutrons at 96.6$\pm 0.6\%$ at an effective frequency of 4 MHz with a beam size of $2.5~\times~2.5$~cm and a wavelength of 0.4 nm. The high frequency and efficiency enable this device to perform high-resolution neutron spectroscopy with comparable performance to currently implemented rf flipper designs. The limitation of the maximum frequency was found due to the field homogeneity of the device. We numerically analyze the maximum possible efficiency of this design using a Bloch solver simulation with magnetic fields generated from finite-element simulations. We also discuss future improvements of the efficiency and frequency to the design based on the experimental and simulation results.