The long-term objective of this project is to qualify Bi-2212 superconducting coils for use in high- field NMR (> 1 GHz-class) magnets, thereby contributing to the mission of NIBIB by improving health by leading the development and accelerating the application of biomedical technologies. Under high magnetic fields, the windings of a superconducting magnet experience very high stresses, which can lead to magnet failure. Therefore, the mechanical design of superconducting wires and coils is key to the success of these high-field magnets. Preliminary research at Wentworth Institute of Technology has demonstrated the strength and ductility of a new super alloy material, designed by Solid Materials Solutions; more extensive testing will be conducted under this proposal. Also, Dr. Voccio is proposing a highly-innovative, lower-cost method of qualifying small 2212 coils by simulating these stresses by high-speed spinning (up to 100,000 rpm) in a cryogenic, vacuum environment. The following are the specific aims:
Specific Aim 1 is to optimize the 2212 wire reinforcement architecture. Dr. Voccio has performed some Preliminary Research in this area, using the WIT Instron testing machines to test the yield strength and ductility of the super alloy strip used by SMS to reinforce the Bi-2212 wire. We will test not only the reinforcing strip but also the fully-reinforced conductor both at room temperature and 77 K in our environmental chamber. These data will allow Dr. Alex Otto of SMS to optimize the Bi-2212 reinforcement strategy, including heat treatment, for these wires.
Specific Aim 2 is to fabricate and test representative 60-mm test coils. Several test coils, using both round and rectangular wire, will be wound by Dr. Voccio and his students. Dr. Rueckart will continue to make Bi-2212 disks to optimize the heat treatment conditions for these coils. Testing will be performed at WIT in the temperature range of 60-77 K using a new Portable Solid Nitrogen Test Station. Liquid helium testing at 4.2 K will be done by Dr. Voccio and the WIT students at the nearby MIT Francis Bitter Magnet Lab.
Specific Aim 3 is to perform spin testing at Barbour-Stockwell. Dr. Voccio and his students will test the 60-mm diameter test coils at speeds up to 100,000 rpm at BSI. After each test, the coil critical current will be measured at Wentworth and BSI using the WIT Portable Solid Nitrogen Test Station. After testing is completed, the best coils will be candidate test coils for future testing by such entities as the MIT Francis Bitter Magnet Laboratory (see Letter of Support).
High temperature superconducting (HTS) wires are an enabling technology for future high-field (> 1 GHz) NMR magnets, and Bi-2212 is the only HTS material which can be made as round wire in long lengths while also showing the promise of persistent-joining capability. Therefore, the purpose of this highly innovative R15 proposal is to use high-speed spin testing, at speeds approaching 100,000 rpm, to mechanically impose the hoop stresses which occur at high magnetic fields (i.e., Lorentz stresses), as this is a lower-cost method to test multiple coils. Successful completion of the project will culminate with candidate coils which can be tested further at high magnetic field at facilities such as the MIT Francis Bitter Magnet Laboratory (see Letter of Support).
