An ultra-compact in-situ³He polarizer for high Q-range SANS: on-beam test and future upgrades

Abstract

He polarizer to be used as a polarization analyzer for separation of incoherent background for soft matter research. The 3 He will be polarized in-situ within a very compact, 18 cm long, magnetic cavity that can be placed between the sample and the detector tank of small-angle scattering diffractometer KWS2 at MLZ [1]. This allows for the angular coverage of 38°, that corresponds to the maximal momentum transfer Qmax=0.85 Å -1 for neutrons with wavelength λ=4.5Å. TheQmax can be extended to 1.28 Å -1 following the recent upgrade of KWS2 for neutron wavelength λ=3Å. The optical pumping will be done by the diode laser array bar frequency narrowed by the ultra-compact volume Bragg grating. The full system will be readily hand transportable and thus useful as an instrument add-on.

in-situ 3He neutron spin filters at JCNS, status and updates

“…This value of polarization was indeed confirmed in commissioning tests using TOF transmission [19] on the ROG instrument at TU-Delft (65%) [20] and in scattering measurements at on the ZOOM instrument at ISIS (62%) [21] within measurement errors. One of our standard chirped volume brag grating lasers [11,7] is used and run at a nominal 40-50W output power. All of the control electronics for temperature control, and NMR FID and AFP are JCNS standard as described previously [7].…”

“…3 He in-situ polarizers currently in construction or planning include the polarization and polariztion analysis for hot neutrons on POLI, polarization analysis for cold neutron SANS on KWS-1 using a magic-box geometry for implementation in conjunction with a high field sample magnet (3 T horizontal and longitudinal) and also KWS-2 using a solenoid geometry for ambient external fields, i.e. no/low sample field, in soft matter applications [11]. Further a thermal beam polarizer is in the planning for the ESS [12] for the T-REX instrument [13] and a similar device for a cold beam polarizer option, funded externally by a Röntgen Ångstrom cluster grant, for the DREAM instrument [14,15].…”

The high-intensity option of the SANS diffractometer KWS-2 at JCNS – characterization and performance of the new multi-megahertz detection system

“…This is a very special correction which, for an unambiguous characterization of the protein morphology, would require measurements using polarized neutrons and polarization analysis. In this way the incoherent free signals from the protein buffer solution and from the buffer solution can be acquired separately from the Q-independent incoherent background (Salhi et al, 2017;Chen et al, 2017). The use of a 3 He spin analyser, as is planned to be used in the near future on KWS-2, should take care of a proper treatment of the inelastic scattering from protonated components in the sample, as reported by Chen et al (2017).…”

“…Moreover, in the case of biological samples, the use of a sample thickness of about 1 mm is required owing to intensity needs. This makes it necessary to involve TOF data acquisition in future polarization analysis experiments on KWS-2 (Salhi et al, 2017). For this purpose, further developments at the sample position are needed, including the installation of a dedicated mini chopper to enable proper TOF acquisition of data at different L D and in order to properly detect the elastic scattering from such samples.…”

Separation of the inelastic and elastic scattering in time-of-flight mode on the pinhole small-angle neutron scattering diffractometer KWS-2

“…This new option will pave the way for a more accurate detection of weak scattering signals from small structures, e.g. from small proteins or short polymer chains in solution, when combined with the wideangle detection option, for reaching Q max = 2 Å À1 , and with the polarization-analysis option using spin-exchange optical pumping (SEOP) polarized 3 He neutron-spin filters (Salhi et al, 2017), which are currently in development at KWS-2.…”