Plasma window

The plasma window (not to be confused with a plasma shield^[1]) is a technology that fills a volume of space with plasma confined by a magnetic field. With current technology, this volume is quite small and the plasma is generated as a flat plane inside a cylindrical space.

Plasma is any gas whose atoms or molecules have been ionized, and is a separate phase of matter. This is most commonly achieved by heating the gas to extremely high temperatures, although other methods exist. Plasma becomes increasingly viscous at higher temperatures, to the point where other matter has trouble passing through.

A plasma window's viscosity allows it to separate gas at standard atmospheric pressure from a total vacuum, and can reportedly withstand a pressure difference of up to nine atmospheres.^[2] At the same time, the plasma window will allow radiation such as laser beams and electron beams to pass. This property is the key to the plasma window's usefulness – the technology of the plasma window permits for radiation that can only be generated in a vacuum to be applied to objects in an atmosphere.^[3][4] Electron-beam welding is a major application of plasma windows, making EBW practical outside a hard vacuum.