Difference in Stability Between Edge and Center in a Rutherford Cable

Keystoned superconducting Rutherford cables are widely used in accelerator magnets like in the LHC at CERN. An essential requirement in the cable design is its stability against local heat releases in the magnet windings originating from for example, strand movement or beam loss. Beam loss is the highest at the coil inner radius of the magnet, where also the magnetic field peaks. Also the local compaction of the cable is maximum here and hence the helium content minimum. When performing stability measurements on several superconducting Nb-Ti cables used in LHC dipole and quadrupole magnets, we observed that the stability against point-like heat disturbances is much worse very close to the cable edges as compared to the central part of the cable. The main reason is related to the geometry of the cable causing variation of many parameters across the cable width, like inter-strand electrical resistance, inter-strand heat conductivity, cooled strand surfaces and RRR. In this paper we show results of new stability experiments and thoroughly compare the data with results obtained with the numerical network model CUDI, which is updated for stability simulations.