Comparative Study of Magnetic Properties for CERN Beam Current Transformers

At CERN, the circulating beam current measurement is provided by two types of transformer, the Direct Current Current Transformer and the Fast Beam Current Transformer. Each transformer is built based on toroidal cores made from a soft magnetic material. Depending on the type of measurement to be performed these cores require different magnetic characteristics for parameters such as permeability, coercivity and the shape of the magnetisation curve. In order to study the effect of changes in these parameters on the current transformers, several interesting raw materials based on their as-cast properties were selected. The materials have been characterised to determine their crystallisation, melting and Curie Temperatures in order to determine suitable annealing processes to tailor their properties. They have been analysed by several techniques including Electron Microscopy and X-ray Diffraction. As-cast magnetic properties such as the permeability, the B-H curve and Barkhausen noise have also been measured to enable the study of the effect of thermal treatment in the microstructure of the alloys, and the correlation of this with the change in the magnetic properties.