polarizing devices
3D CAD model of V shape cavity
multi-channel V-cavity – KWS1, FRM-II
The SANS instrument KWS1 at FRM-II utilizes the concept of a V shape cavity to polarize the neutron beam. In order to realize this concept for the desired wavelength range and within the geometrical specifications (width, length), three parallel channels are assembled.
The plot of the transmission properties across the width of the device is depicted below. The device provides an average polarization of > 93%. Features of the dividing walls and of spots of leakage of the wrong spin state can be identified. The leakage can be avoided in a next generation using a more elaborate design.
- type: multi-channel V-cavity polarizer
- path/profile: straight
- cross-section: 50.00 x 50.00mm˛
- width of channels: 16.47mm
- length: 650mm
- coating: Fe/Si, m = 3.6; non-magn. Ni/Ti, m = 1.2
- substrate: Si-wafer (300 µm), Borofloat
- the polarizer comprises 3 channels with V-cavities
plot of transmitted neutron intensity and beam polarisation as a function of the location across the width of the device
Super-flat polarizer – BL04 magnetism reflectometer, SNS
The specific requirements for the new polarizer for the BL04 magnetism reflectometer at the SNS were: i) highest beam polarization and ii) a super-flat mirror. For i) the latest coating technology for Fe/Si polarizing supermirror was applied providing an excellent reflectivity (R = 80% @ m = 4) yielding a very high polarization of ≈99.5%. In order to achieve the super-flat mirror three particular contributions were taken into count:
- elaborated sample preparation
- dedicated assembly concept
- supermirror coating with virtually zero internal stress to avoid any deformation of the substrate by the coating
In addition to the standard measurement of the waviness the flatness was tested with neutrons, measuring the profile of the reflected beam and comparing it with the profile of the direct beam. Plots at various reflection angles are shown below. The average additional broadening is smaller than 1%.
- type: polarizing mirror
- path/profile: mirror
- width: 60mm
- length: 400mm
- coating: Fe/Si, m = 4
- waviness: 0.04 × 10-4rad (4 × 10-6rad)
- substrate: super-polished Borkron glass
spin dependent reflectivity and polarization of Fe/Si supermirror coating
profile of the neutron beam reflected from the polarizer at various reflection angles compared to the incident beam
V shape cavity - RESEDA FRM-II
V-cavity for RESEDA
pre-assembled elements of V-cavity
The resonance spin echo spectrometer RESEDA utilizes a V shape cavity in front of the instrument to supply a polarized neutron beam. This component is a straight guide unit with silicon wafers inserted in the shape of a V covering the complete width of the beam. The wafers are coated with polarizing Fe/Si supermirror (m = 3) which select the neutrons according to their spin. One spin state is reflected out of the beam and is absorbed in the Borofloat substrate of the side walls. The other spin state is transmitted to the instrument.
- type: V shape cavity polarizer
- path/profile: straight
- cross-section: 36.7 x 36.7mm˛
- length: 2000mm
- coating: Fe/Si, m = 3; non-magn. Ni/Ti, m = 1.2
- substrates: Si-wafer (300 µm), Borofloat
spin dependent transmission and polarization of Fe/Si supermirror coating
polarizing bender - JRR-3M
Polarizing Bender
The compact polarizing beam bender comprises 23 thin glass vanes (0.2 mm) which are bent to a radius of 24m. The vanes are coated with polarizing FeCoV/TiN supermirror. In order to suppress total reflection of neutrons from the substrate an absorption layer is initially deposited. Permanent magnets are incorporated in the casing to provide the vertical guide field.
- type: multi-channel polarizing bender – 22 channels
- path/profile: truly curved - R = 24m
- cross-section: 20 x 20mm˛
- length: 440mm
- coating: FeCoV/TiN, m = 2.8
- substrate: 0.2 mm glass vanes
- aluminum / soft iron casing with permanent magnets incorporated
spin dependent reflectivity and polarization of FeCoV/TiN supermirror coating
