Study on Magneto-Resistance Sensors for Low Magnetic Field Measurements

High-Q operation of a superconducting radio frequency cavity can reduce the power loss at the surface and is desirable for continuous-wave operation. To realize the high-Q operation, the surface resistance, which is a sum of the Barden-Cooper-Schrieffer resistance and residual resistance, needs to be reduced. The residual resistance has been found to originate primarily from the magnetic flux trapping in defects in the cavity during the cooling down process. A magnetometer called the “flux gate sensor” has been used to measure the ambient magnetic field; however, this is larger in comparison with the cavity and it is very expensive. Sensors based on the magneto-resistance effect, such as the Anisotropic-Magneto-Resistance (AMR) sensor, are smaller and much less expensive than a flux gate sensor. We examined the characteristics of the magneto-resistance sensors at room temperature and liquid nitrogen temperature. The results are reported in this paper.