The Layer Cake

Andrei Sakharov had arrived at Arzamas-16 in 1948 with his mentor Igor Tamm. Kurchatov had asked Tamm if he could help confirm the mathematical results that other scientists had already calculated. Sakharov, who recently received his Ph.D. under Tamm, followed him to Arzamas-16 to assist with the plans.

Sakharov found some faults in the "tube" plan that Zeldovich's team had formulated. He designed his own plan, which he called the "layer cake." His idea was to place alternating layers of the fusionable material (tritium and deuterium) between layers of fissionable fuel (uranium). Vitalii Ginzburg, another of Tamm's students, added one improvement, and everyone including Zeldovich agreed with the new plan.

The Soviets had a workable idea by the end of 1948, before they had tested their first atomic bomb. But they waited until after the test before they started to build their hydrogen bomb.

Zeldovich was the head of the theoretical department at Arzamas-16.