The concept and development of fusion reactors based on the confinement of a high temperature plasma with magnetic fields has been approached from many perspectives. However, utilizing the effects of magnetic fields on charged particles has, in general, led to systems wherein the magnetic field lines are either open-as in the case of the magnetic mirror previously discussed-or closed-as for the case of toroidal devices. We first consider the former, following historically the development of magnetic confinement devices which began with open field line systems.