In situ polarized 3He system for the Magnetism Reflectometer at the Spallation Neutron Source

Abstract

We report on the in situ polarized (3)He neutron polarization analyzer developed for the time-of-flight Magnetism Reflectometer at the Spallation Neutron Source at Oak Ridge National Laboratory. Using the spin exchange optical pumping method, we achieved a (3)He polarization of 76% ± 1% and maintained it for the entire three-day duration of the test experiment. Based on transmission measurements with unpolarized neutrons, we show that the average analyzing efficiency of the (3)He system is 98% for the neutron wavelength band of 2-5 Å. Using a highly polarized incident neutron beam produced by a supermirror bender polarizer, we obtained a flipping ratio of >100 with a transmission of 25% for polarized neutrons, averaged over the wavelength band of 2-5 Å. After the cell was depolarized for transmission measurements, it was reproducibly polarized and this performance was maintained for three weeks. A high quality polarization analysis experiment was performed on a reference sample of Fe/Cr multilayer with strong spin-flip off-specular scattering. Using a combination of the position sensitive detector, time-of-flight method, and the excellent parameters of the (3)He cell, the polarization analysis of the two-dimensional maps of reflected, refracted, and off-specular scattered intensity above and below the horizon were obtained, simultaneously.

Optically polarizedHe3

“…With TOF analysis, T 0 vs. wavelength can be fit, allowing extraction of the opacity and T e for a filled cell. Using this approach, determinations of P He at pulsed sources with uncertainties of 2% have been reported (Chupp et al , 2007; Tong et al , 2012). …”

“…An in-situ NSF has been operated routinely on the Magnetism Reflectometer at the SNS 21 (Tong et al , 2012) and smaller in-situ systems have been developed for the HB3 triple-axis spectrometer and the hybrid spectrometer (HYSPEC) at the SNS (Jiang et al , 2014). At LENS 22 , a continuously pumped analyzer has been demonstrated for spin echo small angle neutron scattering (SESANS) (Parnell et al , 2015).…”

Development of a compact in situ polarized 3He neutron spin filter at Oak Ridge National Laboratory

“…At Oak Ridge National Laboratory (ORNL), a first generation in situ system based on SEOP has been built and tested on the Magnetism Reflectometer at the Spallation Neutron Source (SNS). 11 Although this system provides good neutron polarization and transmission, its dimension along the neutron pathway (100 cm) renders it impossible to use on other instruments at ORNL. In an effort to make the system compatible with as many instruments as possible, we constructed a second generation compact in situ system also based on SEOP, which only occupies 50 cm along the neutron pathway.…”

Development of stable, narrow spectral line-width, fiber delivered laser source for spin exchange optical pumping

“…Highpower, spectral narrowed lasers with good stability are the key to the success of SEOP. In the in situ optically pumped NSF demonstrated at the Spallation Neutron Source at Oak Ridge National Laboratory [14], free-space delivered 500 W laser diode arrays with 0.6 nm spectral bandwidth were used to perform the optical pumping. However, such laser diode arrays are not the best choice for high-efficiency optical pumping applications.…”