Filling up the spin filter with polarised helium-3

See how anxious the experimental team is while preparing the very first spin filter bottle prior its installation on the instrument.

• W. Heil (left) and H. Humblot (middle) working on the ³He polariser.
• A series of cells are filled with 0.7 mbar of pure ³He atoms. The discharge applied in the cells put the ³He atoms in a metastable state. A laser light, circularly polarised with its axis parallel to the applied magnetic field, pump the gas and the obtained 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 removed from the compressor by W. Heil once filled with the polarised gas under a pressure of several atmospheres. 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 cell inside the Cryopad-II in which they had trapped a magnetic field (Meissner effect). At the time, they had no better magnetostatic cavity for maintaining the ³He polarisation for long times..
• F. Tasset is looking at the ratemeter to get a first estimate of the neutron-beam polarisation.

Reference
1- H. Humblot, W. Heil, E. Lelièvre-Berna & F. Tasset, Neutron News 8 (1997) 27. DOI: 10.1080/10448639708231997