High magnetic fields are integrated in our daily life. For example, they are used routinely in magnetic resonance services at many hospitals. Permanent magnets are found in many applications in industry and the search of new magnetic materials is a very active area relevant, for instance, to improve the energy efficiency in motors or generators.
The strongest field produced by a permanent magnet is 2T (Fig. 1). In order to generate higher magnetic fields, electromagnets need to be used, in general, solenoids made by winding an electrical conductor. The construction of solenoids faces two important problems. On the one hand, the field generated by the electromagnet produces stress in the conductor that increases as the field squared. On the other hand, the electrical resistance of the conductor generates heat, consuming large amounts of electrical energy and cooling.
The energy stored in the magnet, which is proportional to the volume integral of the field squared, is the parameter used to characterize the performance of a magnet. As a matter of fact, to build and operate an 8T magnet able to house inside it a human is as complicated as to make a 20T magnet for magnetic resonance analysis in applications that require a space of a few centimeters. The Field/Temperature (B/T) parameter is another parameter proportional to the complexity of the facility. Difficult magnets are operated in an adequate environment, a large facility laboratory, open to external users. Large High Magnetic Field Facilities are:
- European Magnetic Field Laboratory (EMFL, Europe) which coordinates four large European high magnetic field facilities:
- The Grenoble High Magnetic Field Laboratory (GHMFL) , Grenoble (France). DC field Facility. Maximum field of 35T. A 42.5 T hybrid magnet is under developing.
- The Laboratoire National des Champs Magnétiques Pulsés (LNCMP), in Toulouse (France). Pulsed Magnetic Field Facility. Maximum field 81.3T, offering the longest field pulse above 70T in the world (10.2 ms).
- The Hochfeld-Magnetlabor Dresden (HLD), in Dresden (Germany). Pulsed Magnetic Field Facility. Maximum field of 94.2T. Record magnetic field in Europe.
- The High Field Magnet Laboratory (HFML) in Nijmegen (Netherlands). DC field Facility. Maximum of field 33T. A 38T resistive magnet and a 45T hybrid magnet are being developed.
- National High Magnetic Field Laboratory (NHMFL, USA) with facilities at:
- The Magnet Lab at Florida State University ( Tallahassee site), Florida. DC Field Facility. The World’s strongest magnet, the 45 T hybrid magnet requires 33MW to operate and more than 15,000 liters of water every minute for cooling the resistive part.
- Los Alamos National Laboratory (LANL), Los Alamos (New Mexico). Pulsed Field Facility. World’s record for pulsed magnetic fields, in excess of 100 T, using non-destructive coils.
- Wuhan National High Magnetic Field Center (WHMFC), Wuhan (China). Pulsed magnetic field facility open for external users in 2013. Maximum field of 83 T.
- International Megagauss Science Laboratory (MGSL), Tokyo (Japan). Pulsed magnetic field up to 80T by non destructive magnets and up to 80 Tesla and from 100 up to 730 T (the world strongest as an indoor record) by destructive (the single turn coil and the electro-magnetic flux compression) methods.
Other magnetic field facilities are:
- Long Pulse Magnet Facility in Zaragoza, Spain (31T, 2000 ms).
- Wills Physics Laboratory, Bristol (UK). Pulsed fields up to 60 T
- Pulsed Field Facility in Leuven (Belgium). Fields up to 55 T.