R & D studies on mechanical stress of 1GHz NMR magnet

In order to make a 1GHz NMR magnet compact, it is operated under high hoop- stress conditions, In our design the hoop-stress of a 1GHzNMR magnet exceed s 180 MPa. We prepared two types of sample coils. One of them was construct ed with niobium-tin superconducting wire, which has a tantalum core. The ot her one was wound with niobium-titanium superconducting wire. These wires a re rectangular in cross-section. The niobium-tin sample coil was energized in a backup magnetic field of 13.5 T and 14 T, It was possible to operate i t up to a hoop-stress of 272 MPa. The niobium-titanium sample coil was test ed up to 99% of its critical current where the hoop-stress was 226 MPa. The se results confirm that our design of the 1GHz NMR magnet is appropriate.