The interior of the
consists of either a vacuum or a helium gas at a very low pressure.
If these contraptions are surrounded by dense atmosphere, they must
be enclosed in a vacuum chamber. When the projectile leaves the
chamber, a large volume of air leaks in before the valve is closed.
To reduce the leak, plasma is placed between the chamber and the
valve. The low density and high viscosity of the plasma reduce the
leak by 3 orders of magnitude. A vacuum pump aided by a simple
plasma window made by Ady Hershcovitch reduced pressure
inside a vacuum chamber to 350 mTorr. Several plasma windows
arranged in a row would completely eliminate the leak. Plasmatron
may prove to be a better way to make plasma in large windows than
electrodes used by Ady Hershcovitch.
Gas guns located in outer space will leak too much gas propellant
unless they are sealed with plasma windows. The most likely
application for such a gun is transportation of raw materials from the
Moon to Earth orbit.
Plasma windows consume large amount of electric power, so
they should be aided by silencer-shaped baffles and gate valves.
"High-pressure arcs as vacuum-atmosphere interface and plasma lens
for nonvacuum electron beam welding machines, electron beam melting,
and nonvacuum ion material modification," Journal of Applied
Physics, Vol. 78, No. 9, November 1 1995, pp. 5283-5288.
Web page at Brookhaven National Laboratory.
Plasmatron at von Karman Institute in Belgium.