Beam Me Up: Using Plasma To Cool Electronics in Space
Researchers have discovered a way to cool spacecraft electronics using a cooling effect caused by high-energy plasmas.
Earth's matter exists primarily as a liquid, solid, or gas. There is, however, a fourth state of matter called plasma. While relatively rare on Earth (it exists in lightning bolts, for example), it is the most common form of matter in the universe, as it is the stuff stars are made of. Plasmas are created when gases are energized to the point where a chemical reaction occurs that untethers electrons from their orbits around atomic nuclei, releasing a flow of photons, ions, and electrons as well as other highly energetic subatomic particles.
Freeze ray technology for the Air Force. Image used courtesy of the University of Virginia
Plasmas are usually known for their high-temperature characteristics, so it is somewhat surprising that researchers at the University of Virginia (UVA) are exploring ways to use plasma beams to cool electronic devices inside spacecraft and high-altitude jet aircraft.
Keeping Electronics Cool
Keeping electronics cool within the Earth's atmosphere is usually a matter of flowing more air over a device using ducting. At extremely high altitudes where the air is very thin or in the vacuum of space, airflow can’t be used to cool vital electronic components, and another method must be employed. Liquid coolants can be brought onboard the craft, but this increases weight and reduces performance and efficiency. One typical solution is to place electronics on a “chill plate” that conducts the heat away from the electronics toward radiators that release it by radiation. However, this may not always be sufficient for high-powered electronic systems.
Plasma Effects on Electronics
The UVA team fired a purple jet of plasma generated from helium through a hollow needle encased in ceramic. A gold-plated surface was used as a target. The researchers were surprised to see that the surface cooled first, then it would heat up. They eventually realized that the surface cooling must have resulted from the evaporation of an ultrathin, hard-to-see surface layer composed of carbon and water molecules.
This process is similar to when cool water evaporates off of our skin after a swim. The evaporation of water molecules on the body requires energy, which is taken from the body, making us feel cold. In the case of the plasma, the plasma rips off the absorbed species, releasing energy and cooling the surface.
The team used a microscope process called "time-resolved optical thermometry" to observe the effect and measured something called "thermoreflectance." Hot surfaces reflect light differently than cold surfaces, and this difference can be used to detect cooling. The specialized microscope is needed because the plasma would otherwise obliterate any temperature gauges in contact with the surface.
The researchers were able to reduce the temperature of the surface by several degrees and for a few microseconds. The effect, while small, is enough to make a difference in some electronic devices.
The team is still exploring the potential applications of their discovery. They are interested in using plasma cooling to improve solar cell, LED, and other electronic device performance and for cooling spacecraft surfaces and other objects in space.
What's Next for Plasma Cooling Technology?
The team is working on several projects to develop their plasma cooling technology further. They are exploring using different gases to see how they impact the cooling effect. They are also experimenting with other materials, such as copper and semiconductors, to see how they react to plasma cooling.
The team is also developing a more portable version of their microscopes to allow them to conduct experiments in a wider range of settings, such as in the field or factories.
