Some experiments, especially in fundamental physics, require the complete absence of magnetic fields. The only places you would find such a spot would be either in intergalactic space or inside a superconductor. Now an international team of researchers claim to have created such a space with a magnetic field that is the weakest in the solar system.
In the Journal of Applied Physics of 14 May the researchers report that by building a box consisting of metal shields arranged in a "Russian nesting doll" structure, they have been able to attenuate changes in the ambient magnetic field caused by man, such as passing cars, or of natural origin, such as solar flares, by a million fold, a factor they have increased to seven million since the acceptance of their paper. In practical terms, the shielded box can reduce magnetic disturbances from passing cars to below one pico Tesla. In comparison, the magnetic field of the Earth averages 48 microtesla at the surface.
This million-fold attentuation is an increase of two orders of magnitude over the previous best magnetically shielded space, the BMSR-2 in Berlin, explains Peter Fierlinger, a physicist at the Technical University Munich, Germany. "There is a very fundamental experiment that we are intending to do. It will allow us to look at the origin of the universe much closer to the Big Bang than the Large Hadron Collider," says Fierlinger.
The team of 19 researchers from Germany, Switzerland and the United Sates used an industrial alloy of nickel and iron, Magnifer, that responds to external magnetic fields by becoming easily magnetized and redirecting the magnetic field lines towards the inside of the metal. The complete magnetic shield has a large external chamber consisting of three alloy shields and an aluminum shield for stopping RF radiation. A second box, also consisting of three Magnifer shells, called the "insert," is mounted on rails and can be rolled in and out of the external shield. The total space available for experiments is slightly more than 4 m3.
"You can lock yourself in this room, but you will be the most magnetic item inside," says Fierlinger.
Although such magnetic shields have been built in the past, an efficient design, with optimized spacing and thickness of the metal sheets, became possible with advances in numeric modeling over the last few years, explains Fierlinger. "It took us several years of elaborate work to achieve this improvement," he says.
The magnetic field the researchers achieved is now low enough to tackle an experiment that will allow them to probe the Standard Model of Particle Physics beyond the capabilities of the LHC.
"We are trying to measure the electric dipole moment of the neutron, and this is a very fundamental quantity, it is a quantum effect inside the neutron which is forbidden by the laws of nature that are part of the Standard Model of Particle Physics, but it is an effect required to explain physics beyond our Standard Model,” says Fierlinger. “And this physics must exist because it would explain why the universe, as we see it, has more matter than antimatter."
However, he is quick to add that their magnetically shielded room will profit other areas of science and technology, such as measuring magnetic signals from the brain with SQUIDs, the design and testing of SQUIDs, superconducting detectors, and low-noise electronics. "Our chamber will not be a user facility, but experiments will be collaborative."