Effect of Fast Neutron Irradiation at Low Temperature on NbZr Coil Performance

The effects of exposure to fast neutron radiation on the performance of a superconducting NbZr solenoid are reported. The irradiations and tests were carried out with the coil held near its operating temperature. Performance was determined by measuring the maximum current at which the coil quenched. Secondary irradiation from the 60-in ANL Cyclotron (1.2 × 109 neutrons/cm2/s at 3-13 MeV, peaked at 8 MeV) had no measurable effect upon the operation of the coil. At the ANL CP-5 reactor, a total dosage of 7.2 × 1017 neutrons/cm2 (fission neutrons above 0.7 MeV) caused no deterioration in the coil. A slight enhancement (2 to 3%) of coil performance was observed but this annealed out at room temperature. An exposure rate of 8.3 × 1011 neutrons/cm2/s produced sufficient nuclear heating to give severe degradation in coil performance to 20% of the initial quench current.