Improved Stability of Nb3Sn Superconductor by Increasing Specific Heat

This proposal is submitted in response to the SBIR/STTR High Energy Physics Topic 33a, “Superconductor Technologies for Particle Accelerators, Grant applications are sought to develop new or improved Nb3Sn superconducting wire for high field magnets that operate at 16 Tesla (T) field and higher. Cost-effective Nb3Sn superconducting magnets with operating fields of 16 T are being considered for the LHC energy upgrade (HE-LHC) or a Future Very High Energy pp Collider (VHEppC). However, the instability of superconductors due to perturbations is a key issue for the design and operation of superconducting magnets. Superconductors in operating magnets are inevitably exposed to a variety of disturbances (such as epoxy cracking or conductor motions) which generate heat and can raise temperatures of the superconductors above their critical temperatures – in which case superconductorslose the capability to carry supercurrents, so magnet operation must be terminated immediately. The currents and fields can increase gradually by quenching the magnets for a number of times (which is termed “training”). Efforts in developing Nb3Sn dipole and quadrupole magnets in recent years show that Nb3Sn magnets are less stable and have slower training rates than NbTi magnets: most Nb3Sn dipole and quadrupole magnets require long trainings (usually >20 quenches) to reach 80%–90% of theirshort sample limits. Magnet training is a very costly and time-consuming procedure, so complete training is not feasible for large projects (e.g., the planned Future Circular Collider – FCC, which has ~5000 dipole magnets, for which 14% operational margin is set for the baseline design to reduce magnet costs). Therefore, it is very desirable to minimize Nb3Sn magnet training by improving the stability of superconducting magnets. In this Phase I, we will develop techniques to introduce materials with extremely high specific heat at cryogenic temperatures in the Nb3Sn strand to present high-Jc Nb3Sn wires using schemes that are friendly for wire manufacture. We will use materials with very high specific heat at cryogenic temperatures. The specific heat of these materials is hundreds of times higher than Cu and Nb3Sn. The adding of these materials to Nb3Sn strands using the schemes developed by Fermi Lab and Hyper Tech is expected not to cause difficulty during strand processing, or impact the important strand parameters such as non-Cu Jc, or whole-wire Je, or RRR. The other commercial applications of this advanced Nb3Sn strands are high field 7-11T MRI, NMR systems, superconducting accelerators - protron radiation for cancer treatment, SMES, and high field magnetic separation. According to a U.S. EPA article, more than 97% of the 15,000 accelerators in use around the world have commercial applications, e.g. in the diagnosis and treatment of cancer, the locating of oil and minerals in the earth, the processing of semiconductor chips for computers, the determination of the age of materials through radiocarbon dating, the sterilizing of medical equipment and food products.