Monitoring of static magnetic field and variable electromagnetic fields in a large magnetic fusion plasma experimental facility

The environmental static magnetic field and electromagnetic fields of various frequencies were measured around the Large Helical Device (LHD), a fusion plasma facility located in Japan. The LHD uses a superconducting magnet coil system and high-power plasma heating devices. Usually, leakage of the static magnetic field strength was less than 0.1 mT, but it varied according to the experimental conditions and protection of the operating coils. Leakage of the electric and magnetic fields from the Ion Cyclotron Range of Frequency (ICRF) plasma heating sources of 25-100 MHz were observed in bursts of either a short time or a long time according to particular plasma experiments, but the measured leaks were less than occupational regulation levels. Also, extremely low frequency (ELF) electromagnetic levels were measured near the magnetic coil power supply boxes, and high magnetic strength was observed. As a whole, the electromagnetic fields of the magnetic fusion experimental facility have various frequencies and time-dependent variable fields. Therefore, this facility should be precisely monitored to make proposal for a suitable safety management system.