Laboratory Equipment has more on the Helmholz coil (a bit of antique lab machinery) and how one of its strange qualities might help Sandia’s “Z machine” fusion experiment create the pollution-free power of tomorrow:
A Helmholz coil produces a magnetic field when electrified. In recent experiments, two Helmholz coils, installed to provide a secondary magnetic field to Z’s huge one, unexpectedly altered and slowed the growth of the magneto-Rayleigh-Taylor instabilities, an unavoidable, game-ending plasma distortion that usually spins quickly out of control and has sunk past efforts to achieve controlled fusion. “Our experiments dramatically altered the nature of the instability,” says Sandia physicist Tom Awe. “We don’t yet understand all the implications, but it’s become a different beast, which is an exciting physics result.”
Researchers placed the Helmholz coils around a liner containing deuterium so the coils’ magnetic field lines soaked both container and fuel over a period of milliseconds. The relatively slow process, like soaking bread in beaten eggs and milk to make French toast, allowed time for the magnetic field lines to fully permeate the material. Then the liner was crushed in tens of nanoseconds by the massive magnetic implosion generated by Sandia’s Z machine. In previous attempts to use Z’s huge field without the Helmholz coils, radiographs showed instabilities appearing on the exterior of the liner. These disturbances cause the liner’s initially smooth exterior to resemble a stack of metallic washers, or small sausage links separated by horizontal rubber bands.
But firing with the secondary field running clearly altered and slowed formation of the instability as the liner quickly shrank to a fraction of its initial diameter. Introducing the secondary magnetic field seemed to realign the instabilities from simple circles — stacked washers, or rubber bands around sausages — into a helical pattern that more resembled the slanting patchwork of a plaid sweater.
Laboratory Equipment is keeping its offices too cold, I think – that writer is dreaming of warm, comfortable things.
You can read more about Helmholtz coils here – they basically consist of two rings that help stretch out a magnetic field so that the lines of force between them are just about parallel.