The Effect of Transverse Pressure on the Inter-Strand Coupling Loss of Rutherford Type of Cables

Abstract

In the framework of the LHC magnet development program at CERN, the effect of transverse pressure on the inter-strand coupling loss of Rutherford type of cables has been investigated. For this purpose a special measuring set-up is designed to measure calorimetrically the AC loss of a stack of keystoned cable pieces for an applied transverse pressure of up to 130 MPa. An AC dipole produces a varying magnetic field with a maximum amplitude of 1 T; the stack of cable pieces can be rotated with respect to the AC dipole in order to distinguish the inter-filament coupling loss from the inter-strand coupling loss. Measurements are presented of a NbTi cable with tinned strands as envisaged to be used for the inner layer of the LHC main bending dipoles. The inter-strand coupling loss increases strongly for higher pressures. The contact resistance Rc between crossing strands, as determined using a network model for the cable, varies between about 7 and 1 μΩ for pressures between 5 and 100 MPa respectively. The small Rc value at 100 MPa corresponds well with AC loss measurements on a model magnet in which a similar cable is used.