SIMPLE METHOD FOR MEASUREMENT OF DECAY-RATE IN SUPERCONDUCTING MAGNET

We have fabricated a simple and inexpensive sensor for measurements of decay rate of a magnetic field under a persistent mode in superconduc ting magnets using the magnetoresistance of a commercial copper wire o f 0.1 mm diameter. We have found that the magnetoresistance of the cop per wire has good reproducibility and no hysteresis up to 15 T at 4.2 K. Using this copper wire sensor, we can measure the decay rate with a n accuracy of 1 ppm in the persistent mode of 15 T at 4.2 K. We also f ound that commercial GaAs Hall elements can be used for low temperatur es experiments and that this copper wire sensor has advantages in term s of reproducibility and hysteresis compared with GaAs Hall elements.