Material is a key issue for the high field magnet development. For DC resistive magnets, copper alloys with high strength and high electrical conductivity from room temperature up to 200 °C are required.
Steady high field resistive magnets developed worldwide used mainly two technologies: the Bitter and the polyhelix one. Each technology encounters material limits.
In the case of Bitter, magnets are made of thin plates (from 0.2 to 1 mm) up to 1000 mm in diameter. High performance Copper alloys with a high content of Silver (classically 18 wt.%, with a yield strength ranging between 800 to 1000 MPa and a minimum of conductivity at room temperature of 50 MS.m-1) have been industrialized by one company up to 250 mm in diameter. For the need of larger diameters, copper plates with a possible addition of a low content of Silver are proposed by different companies. They give a lower yield strength (between 400 to 450 MPa) and a higher conductivity around 58 MS.m-1. This could be a limitation when optimizing Hybrid magnets where the external superconducting windings increase the forces on the outer most Bitter as compared to stand alone resistive magnets.
For the polyhelix technology a similar limitation is existing: the forged and heat treated tubes needed for the helix magnets exhibit decreasing physical properties with increasing diameters. To overcome this problem, the LNCMI has started a R&D program in 2012 to consolidate an alternative way of production. The Cold Spray technology, classically used for repairing purposes or layer deposition, was adapted for the production of thick tubes of copper alloys. We present the results obtained on a material point of view as well as the field production that was obtained using these new products.