A. Warhead before firing; primary (fission bomb) at top, secondary (fusion fuel) at bottom, all suspended in polystyrene foam. B. High-explosive fires in primary, compressing plutonium core into supercriticality and beginning a fission reaction. C. Fission primary emits X-rays which reflects along the inside of the casing, irradiating the polystyrene foam. D. Polystyrene foam becomes plasma, compressing secondary, and fissile uranium (U-235) sparkplug begins to fission. E. Compressed and heated, lithium-6 deuteride fuel begins fusion reaction, neutron flux causes tamper to fission. A fireball is starting to form...