Magnetic fields yield to a battery of tests

Simulating the mechanics of solar flares produces a surprise. Barry Keily reports.

Collision of two magnetised plasma plumes showing Biermann battery-mediated reconnection.

Jackson Matteucci and Will Fox

A common reaction between interstellar plasma and magnetic fields has been revealed to be more complex than previously thought.

The discovery that the reaction – known as the Biermann battery effect – plays a key part in an astrophysical phenomenon known as magnetic reconnection arose when scientists managed to overcome a primary obstacle in studying it.

Magnetic reconnection is the process in which magnetic field lines tear apart and then snap back together, releasing large amounts of kinetic energy as they do. It occurs throughout the universe and is responsible for several huge and sometimes destructive outcomes, including aurorae, geomagnetic storms and solar flares.

The problem for researchers trying to better understand the forces involved is that these phenomena are huge – requiring mechanics on the scale of a solar system – and are thus impossible to recreate in a laboratory.

Now, however, scientists using the Titan supercomputer at the US Department of Energy's Oak Ridge National Laboratory have succeeded in simulating magnetic reconnection – and the results contained a surprise.

The researchers, led by Jackson Matteucci of the Princeton Plasma Physics Laboratory, also in the US, expanded on recently published ground-breaking Chinese work that studied high energy density plasmas – matter under extreme states of pressure.

The experiments used lasers to blast a pair of plasma bubbles from a solid metal target.

Working with the data produced, Matteucci and colleagues modelled the expansion of the bubbles and found that the Biermann battery effect was deeply implicated in collisions between the expanding plasma and magnetic fields.

The findings showed that the effect can play a significant role in the reconnection occurring when the Earth's magnetosphere interacts with these astrophysical plasmas. The effect first generates magnetic field lines, but then reverses roles and cuts them like scissors slicing a rubber band. The sliced fields then reconnect away from the original reconnection point.

Matteucci says the work of he and his colleagues represents a new platform upon which to study astrophysical phenomena. He will present the findings this week at the Annual Meeting of the American Physical Society’s Division of Plasma Physics, in Fort Lauderdale, Florida.

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