Any easily-magnetized objects (e.g. screwdrivers, wrenches) in the vicinity of high magnetic fields may be attracted very strongly to the magnet. This may result in entrapment and injury as well as cause damage to the instrument, which would lead to quenching, as described later.
High magnetic fields may also cause disruption of medical devices (pacemakers, etc.).
Taking measures for avoiding incidents such as those mentioned above is necessary. It is also desirable to prepare an experimental procedure sheet describing guidelines for safely working around the magnet.
While the magnet is in excitation, only authorized experimental members should be allowed to enter the site. Entry restriction is required for fields of 5 gauss or higher. Please provide the information in advance on the strength of the leakage field around the equipment. It is also required to notify personnel in the vicinity when the magnet is in excitation by posting a notice and using indicator lights. MLF is preparing to install such indicator lights.
MLF standard is
In operation : Lighting RED
Malfunction (generation of quench) : Flashing RED + beep
Please refer to the Cryostat, Refrigerator section for notes on handling cryogen.
A superconducting magnet uses superconducting coils, which are cooled to very low temperatures to achieve zero electrical resistance, to provide for large current and high magnetic field. If the superconducting state is suddenly broken, a phenomenon known as a “Quench”, a large amount of heat is produced, which may vaporize the cryogen. This vaporized cryogen will displace the oxygen in the vicinity of the magnet and produce an asphyxiation hazard. An oxygen content meter must be installed near the magnet or carried by any personnel working near the magnet.
Even if there is no danger of asphyxiation, we require the continuous monitoring of the magnet by personnel at MLF, as a quench generally involves the production of white smoke and may be confused with fire by others in the vicinity. When an indicator light is set to indicate a “Quench” condition and the reporting procedure is stipulated in advance, the operation can be conducted without arranging a watch. Please consult us for the details at the Safety Review.
In the case of an electromagnet power supply, we shall check the standards and specifications of the cables for the power supply input and for the power output to the electromagnet and their connections. We also shall check the operation of an interlock system to shut down the main power in case of any faults causing a current overload above the specification values both of the magnet and the cable connections.
For a cryogen-free superconducting magnet that uses a compressor for cooling, the cabling, etc., of the compressor will be checked for safety.
For details concerning safety measures for electrical equipment, please visit 5. General Notes on Electrical Wiring.
大学共同利用機関法人 高エネルギー加速器研究機構 独立行政法人 日本原子力研究開発機構 J-PARCセンター