It may offer an inexpensive new way to generate a freely movable microplasma, as well as yield insights into fundamental physics questions. It surprisingly also creates a mini light show, with the droplet sparking as it floats above a faint blue glowing gap. It is similar to Leidenfrost levitation — in which droplets dance on a hot vapor cushion. But by creating the vapor with a strong jolt of electricity instead of heat, the researchers found they could ionize the gas into a plasma that glowed a soft blue light.
“This method is probably an easy and original way to make a plasma,” said Cedric Poulain, a physicist at the French Alternative Energies and Atomic Energy Commission. The deformability of a liquid drop would let the researchers rig up a device to move the plasma along a surface.
In their lab, they devised a set-up to run electricity through conductive droplets and film the droplets’ behavior at high speed.. They suspended a small drop of weak HCl, which conducts electricity, above a metal plate and applied a voltage across the drop. When the drop touched the plate, electricity began to flow, and the water in the hydrochloric acid solution started to break down into hydrogen and oxygen gas.
Above 50 volts, the bottom of the droplet started sparking. It levitated, rising over the surface of the plate, and a faint blue glow emanated from the gap.
At first they believed the drop might be resting on a cushion of H2 from the breakup of water, but further analysis revealed that the gaseous cushion was in fact mostly water vaporized by energy from the electric current. The blue light emission was unexpected and probably the most exciting feature of the experiment. Although 50 volts is a relatively low voltage, Poulain explained that the tiny gap between the droplet and the metal plate is what gives rise to the very high electric field necessary to generate a long-term and dense plasma with little energy.
The researchers next plan to analyze the composition of the plasma layer. They say it appears to be a superposition of 2 types of plasma that is not well understood. They will also study the fast dynamics at the bottom of the drop just as the sparks begin to fly, which should yield additional insights into the plasma. Although plasma dynamics may seem far removed from the problem of film boiling in nuclear reactors, Poulain is happy about the path the curiosity-driven research has taken the team. http://www.alphagalileo.org/ViewItem.aspx?ItemId=155306&CultureCode=en
A blue glow emanates from beneath a levitating droplet of weak hydrochloric acid. The glow comes from a plasma created when researchers applied above 50 volts of electricity across the droplet.
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