The "death ray" was one version of the charged-particle-beam weapons he cooked up in the late '20s and the '30s. The US Air Force worked on the big version of it, which was supposed to shoot down airplanes and missiles, in the early '50s. Then they dropped it. The official reason was that it was too expensive and would consume too many resources.
However, the Soviets picked it up and were working hard on it during the '70s. Ronald Reagan was responding to CIA reports of how hard the Soviets were working on it when he came up with his response: SDI, or "Star Wars."
-- Ed Huntress