PLASMA WINDOW

The interior of the coilgun, gunsling relay and slingatron 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 via an explosively driven valve, 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. The plasma window lasts a fraction of a second -- long enough to open and close the valve and yet short enough to draw power from a large electromagnet. Plasmatron and shaped charge detonation may prove to be less expensive methods of making plasma than electrodes used by Ady Hershcovitch.

BIBLIOGRAPHY

Ady Hershcovitch, "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.

Discover Magazine, February 1997, p. 20 (Second half of the paper issue is missing.)

Plasmatron at von Karman Institute in Belgium.