By Peter Weiss
When magnetic field lines of opposite orientation cross, snap, and reconnect, the tussle releases energy. Scientists have long suspected that such fierce encounters fuel dramatic temperature leaps in gases of charged particles, or plasmas, on the sun, near Earth, and in laboratory plasma studies.
New experiments at Princeton University establish a clear connection between magnetic reconnection and surging temperatures of plasma ions, the experimenters say.
“For once, we have a complete picture of that happening,” says Scott C. Hsu, now at the California Institute of Technology in Pasadena. “It’s a very promising thing for people hypothesizing what’s going on up there on the sun,” he adds. Hsu and his colleagues at the Princeton Plasma Physics Laboratory report their results in the April 24 Physical Review Letters.
The findings present an additional challenge to the so-called classical theory of how reconnection takes place, Hsu says (SN: 3/27/99, p. 200). Earlier experiments had already shown that reconnection happens more quickly and over a larger region of space than classical theory permits. In the classical view, plasma flows driven by reconnection are extremely fast. Their energy turns to heat as they interact with charges in surrounding space and push through background plasma.
The new experiments show that more than twice as much energy flows from magnetic fields into ions as classical processes can account for, says Princeton’s Hantao Ji. Unpublished work suggests that turbulence is heating ions and sapping magnetic field energy, Hsu says.
