Bumpy torus

It is based on a discovery made by a team headed by Ray Dandl at Oak Ridge National Laboratory in the 1960s.

Over a macroscopic time, individual ions bounce back and forth between the two mirror coils, remaining confined within the device.

Actually making such a field arrangement that does not leak fuel for other reasons is difficult, but by the mid-1960s several promising designs had emerged, notably the "tennis ball" or "baseball" configuration, and later, the yin-yang concept.

The bumpy torus is an attempt to correct the mirror's problems both with the interchange instability as well as its natural leakage out the ends.

This may seem obvious at first glance, but the problem with this approach is that the resulting magnetic field is no longer linear down the axis, but curved, which increases the rate of interchange instability.

However, when the machine as a whole is considered, as opposed to examining a single mirror cell, the overall field can be arranged as a net minimum-B configuration.

The ELMO team at Oak Ridge National Laboratory proposed controlling this by injecting high-energy ("hot") electrons into the space between the outside of the mirror confinement field and the outside of the reactor itself.

In particular, the electron shell concept was nowhere near as powerful as predicted, and to add to the problems, the microwave heating system proved to have far lower efficiency than expected.

In 1988, a review of the entire field suggested that the electron confinement simply did not create the conditions needed, and further interest in the concept ended.