Editing Inertial electrostatic confinement (section)

===Core focus===

In 1995, Nevins argued that such machines would need to expend a great deal of energy maintaining ion focus in the center. The ions need to be focused so that they can find one another, collide, and fuse. Over time the positive ions and negative electrons would naturally intermix because of [[electrostatic]] attraction. This causes the focus to be lost. This is core degradation. Nevins argued mathematically, that the fusion gain (ratio of fusion power produced to the power required to maintain the non-equilibrium ion distribution function) is limited to 0.1 assuming that the device is fueled with a mixture of [[deuterium]] and [[tritium]].<ref name=Nevins1995/>

The core focus problem was also identified in fusors by Tim Thorson at the [[University of Wisconsin–Madison]] during his 1996 doctoral work.<ref name="Tim Thorson 1996"/> Charged ions would have some motion before they started accelerating in the center. This motion could be a twisting motion, where the ion had [[angular momentum]], or simply a tangential velocity. This initial motion causes the cloud in the center of the fusor to be unfocused.