#teller-ulam

In the Teller-Ulam hydrogen bomb design, high explosive compresses fission fuel in the "primary" stage. Intense X-rays from the atomic explosion move through the radiation channel, vaporizing the uranium pusher-tamper, which acts like an inside-out rocket, compressing the fusion fuel and spark plug to extreme density. The spark plug becomes a second fission bomb, heating the fusion fuel and igniting the fusion reaction. The uranium shield protects the secondary from destruction while fusion occurs; the explosion is over in microseconds.