Progress in the development of an 88-mm bore 10 T Nb3Sn dipole magnet

A 10 T, 2-layer cos(θ)-dipole model magnet with an 88 mm clear bore utilizing an advanced powder-in-tube Nb₃Sn conductor is being developed for the LHC. A dedicated conductor development program has resulted in a well performing Rutherford cable containing strands that uniquely exhibit both an overall current density of 600 A/mm² @ 11 T and filaments with a diameter of 20 μm. The resistance between crossing strands amounts to 30-70 μΩ by insertion of a stainless steel core. After being exposed to a transverse pressure of 200 MPa identical cables show negligible permanent degradation of the critical current. The mechanical support structure is further optimized in order to reduce the peak stress in the mid-plane to below 130 MPa at full excitation and to control the pre-stress build-up during system assembly. Prior to the manufacturing of the final coils a dummy 2-layer pole is wound, heat-treated at 675°C and vacuum resin impregnated. This paper presents the current status of the magnet development program and highlights in particular the successful conductor development