A new type of radially cooled helices designed for a 25 T magnet

We designed a new magnet yielding a field of 25 T in a 50 mm room temperature bore for a consumed power of 11.2 MW. It consists of four coils electrically in series and hydraulically in parallel. The two outer coils are Bitter stacks which deliver together 14.7 T in a diameter of 163 mm. Two helics made of CuCrZr alloy with an elastic limit of 360 MPa and an electrical conductivity of 85% IACS constitute the inner part of the magnet. The helices are cut out of cylindrical tubes with an electrical discharge machine and produce a field of 10.4 T in 58 mm. The insulation between turns is obtained by a number of 125 μ thick sectors of Kapton, which are maintained by two fiber glass rods. The spaces between the insulators constitute the channels for radial cooling. The high water velocity (about 21 m/s) in the channel results in a relatively low average temperature for the copper. Since July 1994 the magnet has been in operation for several hundred hours and its performance is very encouraging. Presently, it is the only magnet in our facility in which more than 10 MW is dissipated