Design and performance of a superconducting neutron resonance spin flipper

Abstract

Despite the challenges, neutron resonance spin echo still holds the promise to improve upon neutron spin echo for the measurement of slow dynamics in materials. We present a bootstrap, radio frequency neutron spin flipper using high temperature superconducting technology capable of flipping neutron spin with either nonadiabatic or adiabatic modes. A frequency of 2 MHz has been achieved, which would achieve an effective field integral of 0.35 T m for a meter of separation in a neutron resonance spin echo spectrometer at the current device specifications. In bootstrap mode, the self-cancellation of Larmor phase aberrations can be achieved with the appropriate selection of the polarity of the gradient coils.

The linear phase correction of modulation of intensity emerging from zero effort (MIEZE) with magnetic Wollaston prisms

“…With this approach, the resolution function of MIEZE can be modified such that the contrast of the intensity modulation can be maximized at any scattering angle of interest. In contrast to the approach of rotating the RF flippers (Dadisman et al, 2022), the approach with MWPs can shape the wavefront at the sample position precisely such that the correction efficiency is independent of the beam divergence and neutron wavelength. Such a correction approach with MWPs will be demonstrated in a future experiment.…”

“…An alternative approach to allow for the complicated sample environment that involves high magnetic field and depolarizing sample is to use modulation of intensity emerging from zero effort (MIEZE) (Ga ¨hler et al, 1992), which has been demonstrated or routinely operated at several neutron facilities, including Larmor at ISIS (Geerits et al, 2019), ORNL (Brandl et al, 2012;Dadisman et al, 2020;Zhao et al, 2015), CMRR (Liu et al, 2020), RESEDA of FRM-II and VIN ROSE at J-PARC (Hino et al, 2013). Depending on the direction of the static magnetic field inside the radio-frequency (RF) flippers with respect to the beam, there are longitudinal and transverse configurations for MIEZE.…”

“…In reality, the neutrons scattered by a specific location of the sample can be captured by any pixel of the detector and vice versa. The effectiveness of having the detector parallel to the sample surface has also been investigated with McStas simulations (Dadisman et al, 2022); this shows that, to minimize the Larmor phase aberration, the detector needs to be perpendicular to the scattered neutrons instead of the incoming beam. Another approach is to physically rotate the RF flippers (Dadisman et al, 2022) such that the wavefront of the intensity modulation can be shaped spatially to match the scattering angle without changing the neutron TOF from the sample to the detector, but its performance is sensitive to the beam divergence because the space focusing condition is coupled with the time focusing condition and they cannot be independently tuned to be focused towards different planes.…”

“…The employment of MWPs to steer the wavefront of the intensity-modulated neutron beam is very similar to a phased array radar, which can create a beam of radio waves that can be electronically steered to point in different directions without moving the antennas. With such analogy, the approach of rotating the RF flippers is similar to the conventional radar, which rotates physically and steadily to sweep the airspace with a narrow beam (Dadisman et al, 2022). As illustrated in Fig.…”

Optimized signal deduction procedure for the MIEZE spectroscopy technique

“…It is routinely available at the spectrometer RESEDA at the Heinz Maier-Leibnitz Zentrum (Franz & Schro ¨der, 2015) and BL06 at the J-PARC Materials and Life Science Experimental Facility (Kawabata et al, 2006;Hino et al, 2013). Furthermore, MIEZE is being actively developed at the Reactor Institute Delft, the ISIS neutron source (Geerits et al, 2019) and Oak Ridge National Laboratory (Dadisman et al, 2020). In Fig.…”