Progress of the 3He neutron spin filter project at HMI

Abstract Recent progress in the various fields related to the project will be described. On the one hand, the development of suitable and reliable filter cells is a crucial task. Especially further decrease of the wall relaxation rate continues to be important. Therefore, we embarked on coatings made out of Cs suboxides, in particular, Cs 7 O, and compared such cells in an elementary neutron experiment with those simply coated with Cs. To enable wide-angle applications of the 3 He neutron spin filter technique, like reflectometry or small angle scattering, the cell design has been modified in order to get access to scattering angles up to 18°. A new type of transportation unit, well adapted to the requirements of those cells, has been constructed and tested. On the other hand, the construction of a filling station to supply filter cells is indispensable. Although a 3 He polarization degree of 80% during optical pumping had been achieved reliably, further improvements for a novel optical pumping cell has been evaluated prepared and tested. Moreover, progress in the compressor completion is discussed. To integrate it, the rebuilding of the filling station for a flow-through type of operation has been evaluated and afterwards the construction of certain parts upgraded, allowing determination of the polarization in each of the four optical pumping cells which will be part of the filling station in the future.