Composite superconducting wires for fast ramped magnets

Recently the need for fast ramped superconducting magnets in new particle accelerator pushed the development of a new class of NbTi wires able to operate at magnetic ramp rates in the 1T/s range with ac losses that can be handled by ordinary cryogenic systems, e.g. few W/m in long dipoles. During the last decade INFN, in the framework of an international cooperation for the developments of fast ramped superconducting dipoles, launched a wire development program which stepped in three phases of wire design and industrial production. The aim of the program was to develop superconducting wires to be used in the construction of a full size superconducting fast ramped magnet (namely a dipole). This paper describes the main steps towards the development of a low loss superconducting multi filament wire. Three main ideas were the pillars of the development activities: the reduction of the geometrical filament size down to 2 μm, the use of CuMn resistive barriers to reduce the inter filament coupling currents, and the reduction to the minimum allowable value of the twist pitch.