Development of MgB2 Current Distribution Systems for High Energy Particle Colliders

The DOE Office of High Energy Physics (HEP) seeks superconductor development technologies in support of magnets for use in accelerators, storage rings and charged particle beam transport systems. HEP is interested in improved current lead and current distribution systems based on high-temperature superconductors, such as magnesium diboride (MgB2), for application to superconducting accelerator magnets. MgB2 offers the possibility of the fabrication of long-length strand and cables from inexpensive starting materials using conventional metalworking processes. An important advantage of MgB2, especially when high radiation exposure is included, is that its critical temperature (Tc) of 39 K provides a high thermal margin. The two main objectives of the Phase II program are (1) developing MgB2 conductors for meeting the superconducting and mechanical specifications for low field, high amperage, current distribution applications for HEP and (2) demonstrating short lengths of model current distribution sub-cables using the improved conductor design developed in this project. Wires were fabricated using hot isostatic pressing for improving connectivity and current density. Strands doped with TiC were fabricated for improving flux pinning and critical currents. Strands with modified strand geometries were demonstrated and one wire bend test was performed to understand and improve strain sensitivity of MgB2 conductors. One model MgB2 cable was fabricated. We have planned an integrated materials development program that invests significant effort in improving the critical currents of MgB2 superconductors through various methods that aim to improve connectivity. We will also investigate making wires with nano-powder additions to improve properties and with higher copper content to improve stability. Modifications to strand geometry and a series of bend tests will be performed to understand and improve the strain sensitivity of MgB2 conductors. Finally, we aim to demonstrate the actual fabrication of MgB2 sub-cables with reacted wire. Commercial Applications and Other Benefits: The wire and cables developed under this program will have wide ranging benefits. Improving MgB2 will accelerate the wire being developed for commercial applications such as MRI systems, fault current limiters, transformers, generators, motors and military applications. Also, magnesium diboride strands with high Tc (thermal margin) and radiation tolerance may find other near-term accelerator applications in the winding of muon colliders, light-source wiggler and undulator magnets.