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Developments in JRA/PNT at GKSS

R. Kampmann, JRA/PNT-Meeting, May 18, Wien, Österreich. Developments in JRA/PNT at GKSS. REFSANS - GISANS development in PNT Devices for improving the resolution of a reflectometer mechanical Fourier Chopper, polarized device with a fast spin flipper,

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Developments in JRA/PNT at GKSS

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  1. R. Kampmann, JRA/PNT-Meeting, May 18, Wien, Österreich Developments in JRA/PNT at GKSS REFSANS - GISANS development in PNT Devices for improving the resolution of a reflectometer mechanical Fourier Chopper, polarized device with a fast spin flipper, polarized device with a wavelength filter Status and Perspectives

  2. Structure analyses using REFSANS Concentration profile perpendicular to the interface • Specular reflectivity: qi=qf Lateral structures • Off-specular reflectivity: qi ≠qf • Analysis of diffuse surface scattering Air/water interface • All measurements optionally to be performed at the air/water interface Horizontal reflectometer

  3. General requirements on REFSANS • Efficient „conventional“ investigations  e.g.Dl/l ~ 1% (optionally) • Optimal capabilities for the analysis of lateral inhomogeneities (~3nm < R|| < ~10mm) GI-SANS option withDl/l ~ 10 % • Comprehensive investigations on biological samples, especially at the air/water interface • Comprehensive characterizations • - in short time and • - thus by using of only one instrument REFSANS = REF + (GI-) SANS

  4. Overview of design and construction of REFSANS • A: beam guides • B: overview of REFSANS in total • C: chopper system • D: sample

  5. REFSANS: Tilted neutron guide NL-2b ending at the chopper chamber of REFSANS chopper- chamber NL-2b

  6. REFSANS in Conv. Refl. Geometry:Peak and Mean Intensity at Medium Resolution • First measurement • (preliminary result): • - horizontal slit-height smeared beam • collimation length: ~ 8m • divergence: ~ 0.01 mrad that is ~ 1% of 12 mrad • sample slit height: 0.8 mm (meets the demands of sample length of 60mm and qi = 12 mrad • Measured mean peak intensity: • ~ 15,000/s • - Measured intensity scales well with Dl/l, Dq/q

  7. Status of REFSANS and GISANS in JRA/PNT • We have neutrons at REFSANS • First experiments have been successful • All components tested so far work well • First GISANS tests have been started • GISANS development in the frame of JRA/PNT is being started and will be strongly supported by B. Toperverg the next months

  8. Development of polarized devices for improving the l-resolution of reflectometers

  9. Time - distance – diagram of the REFSANS chopper - basics of the double disk chopper: van Well et al. - wavelength resolution: Dl/l ~ [x(SC) – x(MC)] / [x(detector) – x(MC)]

  10. REFSANS-Chopper (2 double discs: MC and SC; Ø = 800 mm) - Fixed position of the MC (starting point of REFSANS) - Variable distance between MC and SC (from ~ 5 cm to 2.2 m) - Window of double discs variable between 0° and 120°

  11. Development of polarized devices for improving the l-resolution of reflectometers • Goal: Perform experiments with a beam of low l-resolution and high intensity • Way(s) - Mechanical Fourier chopper - Electronic Fourier chopper (pol. Neutrons) - wavelength filter (pol. Neutrons)

  12. Mechanical Fourier chopper • Basic technique: • beam is modulated, e.g. by means of a Fourier chopper with a triangularly shaped transmission function • Phase and frequency of the transmission function are varied • High resolution data are obtained by means of e.g. deconvolution or RTOF technique. • Device: Fourier chopper at large distance from the sample needed • Transmission: 50 % if slit height and beam width agree • Transmission: 25 % if slit height is smaller than the beam width (usual case) • Fourier chopper is operated different frequencies • High frequencies are needed to obtain high resolution • Costs, space and operation of the Fourier chopper set strong limits • Performance • resolution of Dl/l < 1% can be achieved • Excellent performance expected in combination with a coarse pre-monochromatization (selector or a special chopper as at REFSANS)

  13. Electronic Fourier chopper • Basic technique: • Beam is polarized and pre-monochromatized (e.g. by means of a selector) • Current sheet flipper replaces the Fourier chopper and allows of modulating the beam in spin-up and spin-down neutrons • Neutrons of opposite spin directions are reflected by (component parallel to the field) or pass through an analyzer mirror • Specular reflectivity of both spin components is observed on different positions of the detector • Phase and frequency of the modulation function are varied • High resolution data are obtained by means of e.g. deconvolution or RTOF technique. • Device: Current sheet flipper at large distance from the sample needed • Neutron loss: 50 % due to polarization • Fast electronic beam modulation is a rather easy task and high frequencies and thus high resolution can easily be achieved • Costs, space and operation of the electronic chopper set almost no limits • Performance • resolution of Dl/l < 1% should easily be achieved • Excellent performance expected in combination with a coarse pre-monochromatization (selector or a special chopper as at REFSANS)

  14. Alternative approach: A wavelength filter • Basic technique: • Beam is polarized and pre-monochromatized (e.g. by means of a selector) • Close to the sample position the neutron spin precesses in a coil between ~ 10 p and more than 100 p. • Neutrons of different spin directions are reflected by or pass through an analyzer mirror • Specular reflectivity of both spin components is observed on different positions of the detector • Phase and frequency of the transmission function are varied • High resolution data are obtained by means of e.g. deconvolution or RTOF technique. • Device: Besides polarized neutrons only a rather simple spin rotator close to the sample and a spin analyzer are needed • Neutron loss: 50 % due to polarization • Fast electronic beam modulation is a rather easy task and high frequencies and thus high resolution can easily be achieved • Costs, space and operation of the wavelength filter set almost no limits • Performance • resolution of Dl/l < 1% should easily be achieved • Excellent performance expected in combination with a coarse pre-monochromatization (selector or a special chopper as at REFSANS)

  15. Fourier Chopper compared with the l-Filter • Fourier chopper: At a given time neutrons of well defined wavelengths contribute to the scattering pattern. • l-filter: At a given coil current neutrons of well defined wavelengths contribute to the scattering pattern. •  Similar smearing of the patterns and thus similar deconvolution techniques

  16. Development of polarized devices for improving the l-resolution of reflectometers • Goal in 2006: • Insert and test an electronic Fourier chopper or a l-filter on a selector monochromated reflectometer such as PNR at GKSS. • Goal in 2007: • Insert and test an electronic Fourier chopper or a l-filter in a ToF reflectometer with a coarse l-resolution such as REFSANS at FRM II. • Goals in FP7: • Different forms of electronic spin modulations for applications in • Reflectometry • SANS and USANS • Elastic high resolution diffractometry • Inelastic diffractometry

  17. SP-Chopper (patent application): distance from sample: ~ 40 m resolution 0.1 % < Dl/l < 10 % flux: independent of resolution SP-Chopper, example: resolution: Dl/l: ~ 0,3 % transmission Tmax : ~ 4 % measurement: no frame overlap Structured Pulse Engineering Spectrometer (SPES)Basic design and calculated Fe-Spectrum for 2q=90°

  18. 1 Å 3 Å 20 ms Comparison with other instruments • SP-ToF: • intensity - independent of l - Independent of l-resolution • neutron optics: • vertical focusing • flexible collimation sample environment: • heavy, large, precise movement • detectors: • huge high resolution banks performance of SPES: • gain (SPES/ARES) > 100 • comparable to Engin-X/ISIS • SPES @ High Flux Reactor • gain (SPES) ~ 20 • performance ~ VULCAN@SNS Calc. fluxes for: dl/l=0,3%; Dqh=6 mrad; Dqv: sm (m=2) stationary source, flux: 1014 cm-2s-1, SP-ToF (FRG-1) pulsed source, flux: 1015 cm-2s-1, conv. ToF (e.g. ISIS) stationary source, flux: 1014 cm-2s-1, conv. ToF (e.g. FRG-1) Major Inv. 2.8 Mio €

  19. R. Kampmann, JRA/PNT-Meeting, May 18, Wien, Österreich Summary: Developments in JRA/PNT at GKSS REFSANS - GISANS development - strongly delayed due to delays with REFSANS - Strong activity in the near future and 2007 Devices for improving the resolution of a reflectometer a polarized device with a fast spin flipper or polarized device with a wavelength filter - will be manufactured and tested in 2006 at a selector monochromatized reflectometer (PNR/GKSS) - will be manufactured and tested in 2007 at the ToF- reflectometer (REFSANS) Proposals for FP7: Different forms of electronic spin modulations for applications in Reflectometry, SANS and USANS, Elastic high resolution diffractometry and Inelastic diffractometry

  20. REFSANS-Chopper: Basics t=0: MC closes t=0: SC opens • - time t=0: Neutron guide between MC and SC is filled with neutrons with l < l0. • this neutron package runs to the detector when the SC opens (t=0) • the longer the neutron package the higher the intensity and • the lower the wavelength resolution • - two double disks needed to define the wavelength range to be used

  21. Components inside the chopper chamber(view in beam direction) NGE-4 SC (movable on an x-y-table) NGE-3 NGE-2 MC (fixed position)

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