High magnetic field test of the ITER outer vessel steady-state magnetic field Hall sensors at ITER relevant temperature.

The ITER outer vessel steady-state magnetic field sensor diagnostics consist of sixty sensor units. Each sensor unit features a pair of ceramic-metal Hall sensors with a sensing layer made of bismuth. The sensors were tested simultaneously in the magnetic field ranging from -12 T to +12 T at the temperature range from 27 to 127 °C. The Hall coefficient and magnetoresistance of the bismuth layer related to the sensors were identified. In the sensor operating conditions, the Hall coefficient dependence on temperature was fitted with an exponential function with a relative error of less than 0.08%, and the dependence on the magnetic field was fitted with a Gaussian-like function with a relative error of less than 0.11%. An alternative expression based on the physical understanding of the free charge carrier transport in semimetals was derived to describe the dependence of the Hall coefficient on the magnetic field, and its fitting error of 1.2 mT in terms of the magnetic field measurement has met the ITER measurement accuracy requirements.