Cold Plasma Hovercraft

Back in 1997, researchers at Berkley National Laboratory developed a cold plasma generator dubbed the "Constricted Plasma Source" or CPS. "The beauty of our source is that it can run with virtually any gas," says physicist André Anders of Berkeley Lab's Accelerator and Fusion Research Division. Anders, along with Michael Rubin and Michael Dickinson, who also work at Berkley National Laboratory, won the R&D 100 Award for development of the device.

Anders describes the unique design of the CPS as "beautifully primitive. There's nothing to break." The device works by forcing gas and an electric current through a narrow constriction which may be a single hole, a series of holes, or a narrow slit in a plate between the source's negatively charged cathode and a positively charged anode. As pressure builds in the chamber behind the constriction, ionization of the gas molecules increases resulting in a gas of charged atoms and molecules mixed with free electrons— a plasma. But unlike most plasmas, this one is at room temperature.

The electrons stream through the constriction, attracted toward the anode, which may be a metal grid near the constriction or the target itself. Meanwhile the positively charged ions remain inside the chamber due to their attraction to the cathode. However, as the pressure builds inside the chamber, the less energetic ions are finally ejected through the constriction, the only means of escape.

The process is started when helium is injected into the tube and short high-voltage pulses (under one microsecond) are applied across the electrodes. The resulting discharge in the gap between the electrodes creates a blue plume of plasma up to 5 centimetres in length. Increasing the helium flow rate or the magnitude of the voltage pulses will increase the length of the plume. The plume remains at room temperature and can be touched by bare hands.

Because of the sterilizing effect of plasma and portability of the device, most applications will be in the biomedical industry to kill bacteria, heal wounds and treat plaque. However, if the plasma can be reinforced by an external magnetic field, it may find applications as gas flow restrictors and maybe even force-fields to contain pressure.

One example of a plasma force-field is the plasma window invented at Brookhaven National Laboratory. Plasma windows produced in the lab typically consume about 20kw for every inch in diameter (8kw/cm), but are capable of providing a transparent wall between the vacuum of space and the pressure within a spacecraft. You may not want to get too close though as the plasma temperature can exceed 15,000 Kelvins (26,540 F). Yet, given the significantly lower pressure differential needed to support a hovercraft, a plasma force field at atmospheric pressure and room temperature shouldn't be that far fetched.