Biconic cusp

The biconic cusp was an early method for modeling plasma confinement. They were studied at the Courant Institute in New York by Harold Grad in the late 1950s and early 1960s.
Description.
The magnetic fields in this system were made by electromagnets placed close together. This was a theoretical construct used to model how to contain plasma. The fields were made by two coils of wire facing one another. These electromagnets had poles which faced one another and in the center was a null point in the magnetic field. This was also termed a zero point field. These devices were explored theoretically by Dr. Harold Grad at NYU's Courant Institute in the late 1950s and early 1960s. Because the fields were planar symmetric this plasma system was simple to model.
Particle behavior.
Simulations of these geometries revealed the existence of three classes of particles. The first class moved back and forth far away from the null point. These particles would be reflected close to the poles of the electromagnets and the plane cusp in the center. This reflection was due to the magnetic mirror effect. These are very stable particles, but their motion changes as they radiate energy over time. This radiation loss arose from acceleration or deceleration by the field and can be calculated using the larmor formula. The second particle moved close to the null point in the center. Because particles passed through locations with no magnetic field, their motions could be straight, with an infinite gyroradius. This straight motion caused the particle to make a more erratic path through the fields. The third class of particles was a transition between these types. Biconic cusps were recently revived because of its similar geometry to the Polywell fusion reactor.
Further reading.
Biconic cusp simulation work