A new closed magnet circuit will be soon integrated into the experiment. The circuit design includes two discs of Sm2Co17 magnets, magnetized in opposite directions, as the flux source. The yoke is made of FeNi which has been selected for its high magnetic permeability and its mechanical stability at cryogenic temperatures. The mean diameter of the circular air gap is 250 mm and the width is 13 mm. The magnetic field will have radial symmetry and a magnetic flux density of about 0.5 T.
One of the properties of the system is that the magnets and the air gap are completely screened by a high permeability iron yoke. This should considerably reduce the level of external electromagnetic perturbations detected by the coil. The symmetry of the circuit with respect to the horizontal plane helps to improve the uniformity of the flux density in the air gap.