's death ray
or particle beam weapon, was actually based on a very large Van de Graaff generator
. These generators are designed to put out very high voltages. Tesla's design was to shoot charged microscopic pellets of tungsten
through a cannon like apperatus, using the electrostatic repulsion between the particles and the generator as the source of their kinetic energy
Telsa himself claimed it would be able to destroy planes and tanks over 100 miles away. Whether or not this claim was true (as Tesla and Thomas Edison made some exaggerated claims back then) is up in the air. The design was never built into a working model. Both because it's functionality was in question, and the fact that it called for a Van De Graaff generator larger than a water tower.