Large magnetic fields in small spaces

The Search and Discovery story about hypermagnetized neutron stars (Physics Today, May 2005, page 19) says that 10¹⁶ G is the strongest magnetic field found anywhere in nature or in the laboratory. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory now produces magnetic fields of 8 × 10¹⁸ G. RHIC creates collisions between two 100-GeV beams of gold ions. The magnetic field midway between two gold nuclei that are passing at a distance of 20 fm so that there are no nuclear interactions is 8 × 10¹⁸ G. Within two years the Large Hadron Collider at CERN will smash lead ions together with a total energy of 1000 TeV. The magnetic field there will be 2 × 10²⁰ G. The volume of these magnetic fields is small compared to that in a star, but it is still large enough for elementary-particle studies. As pointed out in the story, the large fields are interesting because they are greater than 4 × 10¹³ G, the critical quantum-electrodynamic field strength at which the vacuum becomes strongly birefringent and displays a number of interesting effects involving photons and electrons.