Invisible Door
Have you ever watched star wars or star trek and wondered how they can have a shuttle bay with no doors to allow vehicles to enter and exit while at the same time ensuring air doesn’t escape.
Is this technology actually science fiction? The answer is yes and no. While we do have the technology to produce an ‘invisible curtain’ separating atmosphere and vacuum, we do not, however, have the technology to build a big invisible shuttle bay barrier that allows spaceships to pass through.
There is a technology currently being used today that is similar to the ‘invisible door’ concept. It can be found in electron beam welding (EBW).
Electron Beam Welding
The simple concept of welding works by using extreme heat to melt the work materials as well as filler material to join them together. This traditional way of welding has many disadvantages. When exposed to air during welding, air can enter and cause air bubbles to form within the molten metal, thus creating a weak weld. Filler material would also need to be sourced and it must be compatible to the material of the components.
Therefore, German physicist by the name of Karl-Heinz Steigerwald developed EBW in the 1950s. to solve these issues. EBW uses a beam of high-velocity electrons to produce heat as it impacts the material and bonds them. A magnetic field is used to focus the beam.
The catch? EBW can only work in a vacuum as the presence of air particles can affect the beam. Electrons in a vacuum can also be accelerated. Although possible, using EBW in a vacuum chamber can be costly and impractical. The size of workpieces is limited by the size of vacuum chambers and onsite welding is not feasible. To solve this, Ady Hershcovitch invented the Plasma windows in the 90s.
Plasma Windows
Plasma windows use plasma that is confined by a magnetic field to create a boundary between a vacuum and the atmosphere.
Plasma is a soup of positively charged and negatively charged particles. It is produced when the negatively-charged electrons are stripped off the atoms which causes the gas to become ionized. It is known as the 4th state of matter. Just like how solid can turn into liquid and thereafter gas when heat is introduced, plasma can be produced by heating the gas to an extremely high temperature (above 10 000 K).
How does plasma produce a boundary layer?
The high temperature of the plasma causes it to have a low density while being more viscous. Since plasma becomes extremely viscous, it prevents plasma and the air to flow over one another. Thus, prevents air from entering the vacuum.
Gay-luissac’s law states that the pressure of a given amount of gas held at constant volume is directly proportional to temperature. Therefore, plasma is able to support large pressure differentials and prevent air from the atmosphere from entering the vacuum.
Since ions in the plasma are positively charged, they react to magnetic fields. By using a magnetic field, the plasma can be contained in a given space producing a ‘curtain’ as plasma is forced to travel around the field lines.
Why don’t we have plasma windows yet?
While we have accomplished the task of creating a boundary between air and vacuum there are still many limitations. High-temperature plasma is dangerous and prevents objects from passing through. Any object that passes through would simply disintegrate upon contact. Secondly, it requires lots of power and resources to sustain a small plasma window.
To the sci-fi nerds out there, we are still far away from having an open-concept shuttle bay. With the current technology, we can’t produce a plasma window that is big enough to become, a ‘window’.
References
Atteberry, J. (2009, March 24). How Welding Works. Retrieved July 11, 2022, from HowStuffWorks website: https://science.howstuffworks.com/welding3.htm
Brookhaven National Laboratory. (2019, September 5). Plasma Window Technology for Propagating Particle Beams and Radiation from Vacuum to Atmosphere. Retrieved July 11, 2022, from Techbriefs.com website: https://www.techbriefs.com/component/content/article/tb/supplements/etb/briefs/1834
Dekker, C. (2019, August 23). Types of Welding Gases & What They’re Used For. Retrieved July 11, 2022, from WaterWelders website: https://waterwelders.com/types-of-welding-gases
Liley, B. S. (n.d.). plasma | Physics, State of Matter, & Facts. Retrieved July 11, 2022, from Britannica website: https://www.britannica.com/science/plasma-state-of-matter
