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1996 D3 - 1st 3He polariser

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D3: 1st experiment at the ILL with a 3He neutron spin filter (nov. 1996)

Francis Tasset, leader of the 3He project
©2004 ILL, Serge Claisse

This spin filter was for 100 meV energy neutrons.

D3 is a spin polarized hot neutron diffractometer. It offers a unique way of accurately measuring the magnetization distribution within crystals at the atomic level. When equiped with CRYOPAD, very precise spherical polarimetric scattering measurements can be performed. However, the performances of the instrument depends strongly on its ability of producing an intense and well-polarised neutron beam, and then of analyzing the diffracted beams. This is why the ILL has made great efforts to develop new highly efficient polarisation techniques. One of the best successes is the development of a neutron spin filter based on polarized helium-3 gas (3He), in a close collaboration with the University of Mainz (Germany).

At that time, neutrons were polarised either by diffraction (e.g. Heusler monochromators) or reflection (polarising supermirors). Here neutrons were polarised by absorption in a polarised 3He gas, i.e. a gas the nuclear spins of which were polarised through a Metastability Exchange Optical Pumping (MEOP). Hence the experiment showed that passing a neutron beam through a bottle filled up with this polarised gas lead to a final beam which is of one polarisation, even for a wide range of neutron wavelengths (white beam polarisation).

Part-1: Filling up the spin filter with polarised helium-3

The movies below was recorded during the historical experiment of 1996 when the first spin filter was produced and then tested on the neutron diffractometer D3.
This part shows the anxious experimental team preparing the very first spin filter bottle prior its installation on the instrument.

(mp4 - 59 Mi)

©1996, E. Lelièvre-Berna, Institut Laue-Langevin, Grenoble, France.
Movie files (960x640 pixels, duration: 7'34": .mp4 (mp4 - 59 Mi), .webm (webm - 115 Mi).

Sequences of this first movie:

  •  W. Heil (left) and H. Humblot (middle) working on the 3He polariser.
  • The 3He filling station uses laser light to polarise metastable 3He atoms. The gas atoms at low pressure (0.7 mbar) are optically pumped. The resulting electronic polarisation is partially transferred to the nuclei through a hyperfine interaction. When enough nuclear-spins have been polarised, the 3He gas is then compressed in a two-stage non-magnetic titanium compressor. We see H. Humblot adjusting the assembly.
  • The neutron-spin filter cell is filled with the polarised gas at several atmospheres pressure and then is removed from the compressor by W. Heil. The polarisation remains for a long duration inside the bottle. With the help of T. Roberts, he puts the cell in a special container to transport it to D3 without loss of polarisation.
  • W. Heil and H. Humblot carry the filter to the ILL reactor hall where A. Leadbetter (ILL director) is anxiously waiting for them at D3.
  • F. Tasset, H. Humblot and W. Heil install the 3He spin-filter on D3.
  • F. Tasset is looking at the ratemeter to get a first estimate of the neutron-beam polarisation.

Part-2: Testing the 3He neutron spin filter on D3 (nov 1996)

This second movie shows F. Tasset, assisted by H. Humblot and W. Heil installing the spin filter on the D3 diffractometer at the ILL. After several years to develop the technique and the special bottle, this is now the moment of success in actually polarising a neutron beam.

During this experiment, the neutron-beam polarisation achieved by the filter was determined with high accuracy from spin dichroism measurements. It was verified that no significant relaxation was induced by neutron capture, and the wavelength variation of the polarisation down to 0.33 Å was in good agreement with the 1/v dependency of the absorption cross-section.

(mp4 - 10.59 Mi)
©1996, E. Lelièvre-Berna, Institut Laue-Langevin, Grenoble, France.

Movie files (940x360 pixels, duration: 1'40"): .mp4 (mp4 - 10.59 Mi), .webm (webm - 19.07 Mi)

Sequences of this second movie:

  • The cell filled with polarised 3He arrives on D3. The transport container includes two magnetic coils which maintain the polarisation. H. Humblot, F. Tasset, W. Heil and E. Bourgeat-Lami prepare for the measurements.
  • F. Tasset transfers the cell into CRYOPAD which provides a homogeneous magnetic field and also acts as a spin flipper.
  • The movie ends with a brief view of the zero-field polarimeter developed at PNPI (Gatchina, Russia). This polarimeter is capable of measuring very small rotations of the neutron polarisation.

References

  1. H. Humblot, W. Heil, E. Lelièvre-Berna and F. Tasset, "The 3He neutron spin filter at ILL", Neutron News 8, 4 (1997) 27-32.
  2. W. Heil, K.H. Andersen, D. Hofmann, H. Humblot, J. Kulda, E. Lelièvre-Berna, O. Schärpf and F. Tasset, "3He neutron spin filter at ILL'', Physica B 241-243 (1998) 56-63. W. Heil, J. Dreyer, D. Hofmann, H. Humblot, E. Lelièvre-Berna and F. Tasset, 3He neutron spin filter'', Physica B 267-268 (1999) 328-335.
  3. K.H. Andersen, E. Bourgeat-Lami, J. Dreyer, W. Heil, D. Hofmann, H. Humblot, S. Ivanov, J. Kulda, E. Lelièvre-Berna, A. Petoukhov, L.-P. Regnault, T. W. Roberts, J.R. Stewart, F. Tasset, M. Thomas and A.R. Wildes, "Recent news on ILL polarised 3He developments", Physica B 276-278 (2000) 65-66.
  4. T.W. Roberts, H. Humblot, F. Tasset, E. Lelièvre-Berna, A.R. Wildes, A. Ivanov, A.K. Petoukhov, L.-P. Regnault, A.D. Hillier, J. Kulda, J.R. Stewart, M. Thomas, P. Malbert, D. Jullien, Y. Gibert, R. Gay, E. Bourgeat-Lami and R. Chung, "The current status of the 3He neutron spin filter (NSF) project at the ILL", Physica B 297 (2001) 282-287
  5.  E. Lelièvre-Berna, "Novel polarized neutron tools", Advances in Neutron Scattering Instrumentation, Ian Anderson and Bruno Guérard, Editors, Proceedings of SPIE 4785 (2002) 112-125, ISBN 0-8194-4552-5
  6. A. S. Wills, E. Lelièvre-Berna, A. Sella, F.G. Cloke, P.L. Arnold, F. Tasset, J. Schweizer, R. Ballou, "Magnetisation distribution measurements from powders using a 3He spin filter: a test experiment", Physica B 356 (2005) 254-258
  7. A.K. Petoukhov, V. Guillard, K.H. Andersen, E. Bourgeat-Lami, R. Chung, H. Humblot, D. Jullien, E. Lelièvre-Berna, T. Soldner, F. Tasset and M. Thomas, "Compact magnetostatic cavity for polarised 3He neutron spin filter cells", Nuclear Instruments and Methods in Physics Research B 560 (2006) 480-484
  8. E. Lelièvre-Berna, "Mid-term report of the NMI3 neutron spin filter project", Physica B 397 (2007) 162-167
  9. E. Babcock, A. Petoukhov, J. Chastagnier, D. Jullien, E. Lelièvre-Berna, K.H. Andersen, R. Georgii, S. Masalovich, S. Boag, C.D. Frost and S.R. Parnell, "AFP flipper devices: Polarized 3He spin flipper and shorter wavelength neutron flipper", Physica B 397 (2007) 172-175.

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