Biconic cusp

The biconic cusp was one of the earliest suggestions for plasma confinement in a fusion reactor.^[1] It consists of two parallel electromagnets with the current running in opposite directions, creating oppositely directed magnetic fields. The two fields interact to form a "null area" between them where the fusion fuel can be trapped.

Most early work on the cusp design was carried out at the Courant Institute in New York by Harold Grad in the late 1950s and early 1960s. Variations on the basic concept include the picket fence reactor built at Los Alamos in the 1950s and ring reactors. All of these devices leaked their fuel plasma at rates much greater than predicted and most work on the concept ended by the mid-1960s. Mikhail Ioffe later demonstrated why these problems arose.

A later device that shares some design with the cusp is the polywell concept of the 1990s. This can be thought of as multiple cusps arranged in three dimensions.