Development of quadrupole arrays for heavy-ion fusion

Extensive studies have been performed to optimize the design of superconducting quadrupole arrays for beam transport in future heavy-ion fusion accelerators. In these arrays, 20 or more quadrupole coils are densely packed with their axes aligned in parallel. Field strengths between 3 and 5 tesla at the inner coil diameters have been investigated. The aperture of the individual quadrupoles has been varied between 60 mm and 240 mm. The coils have a typical length of 1 m, and special effort has been made to minimize the length of the interconnect region between the array and adjacent accelerator components. The relative orientation of quadrupoles in the array is chosen to optimize field sharing between neighboring cells. In the presented design, field uniformity in the boundary cells is maintained by placing concentric correction coils onto these cells. A novel approach for the mechanical stabilization and alignment of the individual quads in the array has been developed. Since Inertial Fusion Energy has to compete with other long-term energy sources, cost and reliability are major issues of the magnet array. The presented design uses a round NbTi mini-cable, which allows for a cost-effective, highly automated manufacturing of the required superconducting coils. A flexible, 37-strand mini-cable has been developed and prototype manufacturing has started.