Construction of the new polarised hot neutrons single-crystal diffractometer POLI-HEiDi at FRM-II

A new hot neutrons single-crystal diffractometer for magnetic structure investigations with polarised neutrons is under construction now at FRM-II near Munich. The problems by implementing the polarised neutron option on the existing instrument HEiDi lead to the decision to build a parallel instrument especially designed for this purpose, called Polarisation Investigator-HEiDi (POLI-HEiDi). Both options, zero field for spherical polarisation analysis in complex magnetic structures and high magnetic field for flipping ratio measurements to study spin density distributions, should be available at the new instrument. We present the proposed design and construction of POLI-HEiDi. As neutron polarisation method, 3He spin filter cells (NSFC's) are planned to be used. Dedicated filter cell design as well as the results of the first experiments with a 3He NSFC, performed recently at the HEiDi diffractometer by means of compact magnetostatic cavities, are discussed. The novel multifunctional compact device Helium Rotating Polariser (HERO) is presented.