AN EXPERIMENT to create a piece of the Sun on Earth may have helped solve one
of the great mysteries about our nearest star鈥攚hy its diffuse outer
atmosphere is much hotter than its surface.
Scientists have long puzzled over how the Sun鈥檚 corona reaches a million
kelvin when its surface beneath is only a few thousand kelvin. One theory is
that disturbances in the Sun鈥檚 magnetic field called Alfv茅n waves can
transfer heat to the cloud of electrically charged ions and electrons of the
coronal plasma without heating the surface. But testing this idea with a
spacecraft would be impossible because no vehicle could survive the trip.
To get around this, Masayuki Ono and his colleagues at the Princeton Plasma
Physics Laboratory in New Jersey recreated conditions in the corona inside the
National Spherical Torus Experiment, a spherical chamber designed to study
fusion. Inside the sphere, the researchers created a plasma constricted by
magnetic fields which they distorted to produce Alfv茅n waves.
Advertisement
The group saw the temperature of the plasma electrons soar from about 2
million kelvin to 40 million kelvin. They believe the temperature change is
caused by the Alfv茅n waves transferring their energy to the plasma
electrons. 鈥淧articles get kicked from one wave to the next, gaining energy from
each collision,鈥� says Ono. The group will present its work this week at a
conference in Long Beach, California.
Alan Title of Lockheed Martin Missiles & Space Operations in Sunnyvale,
California, says Alfv茅n waves may not be the end of the story. 鈥淚t is
probably the case that there is more than one mechanism involved in heating the
肠辞谤辞苍补.鈥�
