Physicists usually rely on
magnetic fields to harness the power of plasma, the fourth state of matter, in fusion power experiments. But University of Missouri researchers have managed to create rings of plasma that can hold their shape without the use of outside electromagnetic fields—possibly paving the way for a new age of practical fusion power and leading to the creation of new energy storage devices.
Traditional efforts to achieve nuclear fusion have relied upon multi-billion-dollar fusion reactors, called tokamaks, which harness powerful electromagnetic fields to contain the super-heated plasmas resulting from the fusion reactions. The ability to create plasma with self-confining electromagnetic fields in the open air could eliminate the need for external electromagnetic fields in future fusion experiments, and with it, much of the expense.
The researchers created plasma rings about 15 centimeters in diameter that flew through the air across distances up to 60 centimeters. The rings lasted just 10 milliseconds, but reached temperatures greater than the sun's
fiery fusion core
surface at around 6600 to 7700 degrees K (6327 to 7427 degrees C). Plasma physicists suspect that magnetic fields are still involved—but that the plasma rings create their own.
"This plasma has a self-confining magnetic field," said Randy Curry, an engineer and physicist at the University of Missouri in Columbia. "If one can generate and contain it without large magnets involved, of course fusion energy would be an application." But the researchers' success in creating self-contained plasma rings came as a surprise. "We did not expect that," Curry says.
The researchers had been working with exploding wires that vaporize when pulsed power is applied and release a cloud of plasma energy. They had previously only succeeded in making clouds of plasma that lasted less than a millisecond, Curry said.
The breakthrough came from adding more pulsed power to the plasma. Curry and a graduate student injected the added energy into a "second acceleration region" of their lab device, and set up the conditions that allowed the plasma ring to be launched from the device.
Such basic physics research could also lead to better energy storage for both civilian and military applications. Curry's lab plans to examine the possibility of a "plasma capacitor" that stores tens of joules of energy per cubic centimeter, as opposed to traditional capacitors that hold less than one joule per cubic centimeter.
The self-contained plasma rings created in air could also benefit the manufacturing of metals, plastics and semiconductors. Plasma is currently used to help with semiconductor etching and the modification of other surfaces, but requires vacuum containment vessels and expensive electromagnets to remain contained.
The research was originally funded by the U.S. Department of Defense through the Office of Naval Research. Curry's lab aims to secure new funding to build a smaller version of the plasma device about the size of a bread box within the next three to five years.
But Curry also pointed out that such military funding for basic research has collapsed since sequestration took effect and slashed funding across the board for the U.S. government. In that sense, the plasma ring experiment's success also serves as a warning of what the U.S. could miss out on. According to an article in Science magazine published today, the administration's proposed 2014 budget would restore many of those cuts to scientific research.
Image credit: University of Missouri