Polarization optimization of spin-echo small angle scattering instruments

Abstract

The polarization optimization in a small angle scattering spin-echo setup is considered, under the depolarization and phase errors that occur in field transition regions by improper adjustment of inclined magnetized foils as -flippers. Various correction procedures are discussed. In these setups with precession fields perpendicular to the beam directions, corrections can be reduced strongly by the use of -flippers, and for the remaining errors, correction coils can be constructed.

DCD USANS and SESANS: a comparison of two neutron scattering techniques applicable for the study of large-scale structures

“…In principle a much larger divergence can be used. Detailed descriptions of the instrument and its performance are given by Rekveldt et al (2005Rekveldt et al ( , 2008. Other options to realize a SESANS instrument with other precession arms are, for example, discussed by Dalgliesh et al (2011) and Bleuel et al (2008).…”

“…In addition, increasing the instrument operation wavelength from = 2.37 Å to = 4.74 Å would result in a five times higher scattering cross section, because the scattering power is proportional to 2 . Although current SESANS setups, as described by Rekveldt et al (2008) and Plomp et al (2007), often have reduced spinecho polarization at longer wavelengths, these usually arise because long wavelengths are used to reach large values of the spin-echo length z. For measurements made at a particular value of z, echo depolarization due to Larmor phase aberrations is roughly independent of neutron wavelength, whereas echo depolarization due to sample scattering is proportional to the neutron wavelength squared.…”

The use of symmetry to correct Larmor phase aberrations in spin echo scattering angle measurement

“…Each film has the same thickness and is designed to act as a flipper for neutrons of a particular wavelength when it is inclined at a particular angle to the neutron beam. 11 For this reason, the symmetry of the field line integrals in their case should be the same as that of the triangular prisms analyzed here, although it is much less straightforward to calculate the magnitude of the field integrals because finite element codes have to be used. This is equivalent to a geometry in which the flipping action is suppressed and some applied magnetic fields are reversed to yield a pattern of field directions that is exactly the same as Fig.…”

“…In our case, the magnetic field was induced in a thin layer of Permalloy ͑Py͒ electrodeposited on silicon wafers. In fact, the method used by the Delft group makes use of various symmetries to achieve cancellations of phase aberrations that result from noncontainment of the magnetic fields 11 and their architecture turns out to share some symmetry properties with the equipment described here. Unfortunately, the high field has turned out to be a two-edged sword because it places strong constraints on the required thickness uniformity of the magnetic film.…”

Present status and prospects for Spin-Echo Small-Angle Neutron Scattering (SESANS) at PIK neutron source

“…G(δ) is called "SESANS correlation function", which for systems with inhomogeneous density (for example, particulate systems) is related to the density correla tion function ρ(r) [12,13]. Because of its statistical character, a high resolution in δ is often not necessary, especially for δ larger than Fig.…”