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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

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


Structure analyses using refsans
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


General requirements on refsans
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


Overview of design and construction of REFSANS

  • A: beam guides

  • B: overview of REFSANS in total

  • C: chopper system

  • D: sample


Refsans tilted neutron guide nl 2b ending at the chopper chamber of refsans
REFSANS: Tilted neutron guide NL-2b ending at the chopper chamber of REFSANS

chopper- chamber

NL-2b


Refsans in conv refl geometry peak and mean intensity at medium resolution
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


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



Time distance diagram of the refsans chopper
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)]


Refsans chopper 2 double discs mc and sc 800 mm
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°


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)


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)


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)


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)


Fourier chopper compared with the l filter
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


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


Structured pulse engineering spectrometer spes basic design and calculated fe spectrum for 2 q 90

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°


Comparison with other instruments

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 ~ [email protected]

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 €


Summary developments in jra pnt at gkss

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


Refsans chopper basics
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


Components inside the chopper chamber view in beam direction
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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