Application of a Hall sensor for pulsed magnetic field measurement in the FAT-CM FRC experiments.

Collisional merging experiments of a field-reversed configuration (FRC) plasma at the super-Alfvénic velocity have been conducted in the FAT (FRC Amplification via Translation)-CM (Collisional Merging) device. In the experiments, two FRCs are collided and merged in a confinement section with a quasi-static confinement magnetic field. Therefore, it is necessary to measure the high-frequency pulsed magnetic field superposed on a quasi-stationary signal. The magnetic field is generally measured by a magnetic coil probe in the pulse discharge experiments; however, in such measurements, errors arise in the low-frequency band in the conducted FRC experiments. Therefore, a Hall sensor has been applied for low-frequency magnetic field measurements in the FAT-CM experiments. Calibration of the Hall sensor involves confirming that the sensor has a sufficient response speed and linear characteristics for the magnetic field with a rising time of approximately 240 s and that its output voltage does not saturate up to a magnetic field of 0.7 T. Combination of the Hall sensor and the magnetic coil probe ensures a comprehensive measurement of the magnetic field in the range of FAT-CM experiments. In this study, accurate magnetic measurements were performed in a collisional merging experiment in the FAT-CM device by using a combined magnetic diagnostic system.