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DY: Fachverband Dynamik und Statistische Physik
DY 5: Soft matter
DY 5.6: Talk
Monday, March 23, 2009, 16:00–16:15, ZEU 255
A wedge-shaped polarizing analyzer for the TOF spectrometer FOCUS - Ray-trace MC simulations and experiments — •Ralf Ackermann1,2, Uwe Filges3, Michael Schneider1, Jochen Stahn1, Lothar Holitzner3, Thierry Strässle1, Jan Peter Embs1,2, and Rolf Hempelmann1 — 1Saarland University, DE — 2LNS, ETH Zurich and PSI, CH — 3LDM, PSI, CH
For the cold neutron TOF spectrometer FOCUS at the Swiss Spallation Neutron Source, we are developing a polarization option, which can be used, e.g., for the separation of coherent and spin-incoherent scattering contributions. Our design is based on a wedge-shaped stack of horizontally bent polarizing magnetized supermirrors covering continously the entire scattering range of 120 deg. In our setup, we use remanent magnetized FeCoV/NiN supermirrors produced at PSI. The supermirrors are surrounded by a magnetic guide field of 4.5 mT at the center position. Using the neutron ray-trace Monte-Carlo simulations, we calculated polarization and transmission properties of a 4.8 deg section. We performed test measurements on an analyzer prototype consisting of a stack of 30 supermirrors covering about 2 deg. On a polarized incoming beam of 1 mm x 40 mm dimension and varying wavelength we measured polarization values up to 95% and transmission coefficients up to 75% (6 Å). To further optimize the performance of our setup, we performed finite element calculations of the magnetic guide field and checked these results with a measurement after modifying the guide around the analyzer's entry. Results of our simulations and measurements will be presented and discussed here.