Superconducting magnetic Wollaston prism for neutron spin encoding

Area of Science:

• Neutron optics and instrumentation
• Condensed matter physics
• Superconducting devices

Background:

• Magnetic Wollaston prisms spatially split polarized neutron beams based on spin states.
• These prisms are crucial for encoding neutron trajectories into Larmor phase for applications like neutron phase-contrast radiography and SESAME.
• Existing devices face limitations in field uniformity, phase aberration, and neutron polarization preservation.

Purpose of the Study:

• To develop and characterize novel magnetic Wollaston prisms utilizing high-temperature superconducting (HTS) materials.
• To achieve highly uniform magnetic fields and minimize Larmor phase aberration for improved neutron spin manipulation.
• To enhance neutron polarization preservation and enable larger neutron beam capabilities for advanced scattering techniques.

Main Methods:

• Construction of magnetic Wollaston prisms using HTS films and current-carrying HTS tape wound on soft iron pole pieces.
• Utilizing the Meissner effect of HTS films to confine and shape the magnetic field.
• Cooling the device to approximately 30 K using a closed-cycle refrigerator for simplified operation.
• Measuring spin transport efficiency and Larmor phase variation at the NIST Center for Neutron Research.

Main Results:

• The HTS-based magnetic Wollaston prism demonstrated high spin transport efficiency (~98.5%), independent of neutron wavelength and current.
• The device produced a sharp, well-defined, and planar magnetic field transition due to the Meissner effect.
• Measured Larmor phase variation was linear with horizontal position, consistent with simulations, and showed minimal neutron depolarization.
• The prototype device accommodated a large neutron beam (20 mm × 30 mm) and extended SESAME's accessible length scales beyond 10 μm.

Conclusions:

• High-temperature superconducting magnetic Wollaston prisms offer significant advantages over existing technologies.
• These prisms enable precise control of neutron spin states, preserving polarization and minimizing phase aberrations.
• The developed device facilitates enhanced neutron imaging and scattering experiments, particularly for SESAME, with potential for further scaling.