A reactor is proposed in which the principal role of the magnetic field is to reduce the thermal conductivity. A purely toroidal magnetic field confines a plasma whose pressure is almost constant. The plasma is limited in height by two planar electrodes. The density rises as the temperature falls toward the material boundaries to maintain essentially isobaric conditions. Fueling the reactor is a simple by-product of the drift motion of the ions through the reactor, the confinement time being determined by the residence time of transport rather than by diffusion. As in many reactor schemes, the size is large, but not unreasonable. There are unsolved problems requiring research, but these seem addressable with modest temperature plasmas.