Polarisers & Flippers

We propose two cryogenic devices for polarising the beam and flipping the neutron polarisation. The first one, called Cryopol for 'Cryogenic Polariser', is owned by the CEA and made available by the CEA-CRG team on request. The second one, called Cryopol-II, is a new cryogen-free version able to host much larger spin filter cells. Both consist of a superconducting Nb cylinder in which we trap a 8G homogeneous magnetic field upon cooling.

The second-generation Cryopol (i.e. Cryopol-II) has recently be commissioned on D20 for measuring magnetisation distributions in nano-scale and molecular magnets featuring weak magnetisation and anisotropy. Our colleagues from the Neutron Optics team have constructed very large spin filter cells covering the full section of the beam (6 x 20 cm2 at the cell position) and accepting pressures up to 3 bar. We have designed and constructed a special nutator that flips and transports adiabatically the neutron polarisation with better than 99% efficiency at the exit of Cryopol-II. The neutron beam polarisation is continuously recorded with two monitors located before and after Cryopol-II (see function Efficiency2).