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efficiency as given by the Rankine cycle, the possibility of extremely high coolant temperatures in a plasma reactor are particularly attractive.

        A brief survey of recent plasma reactor* research will be indicative of the wide range of problems which are being studied. The basic plasma core concept is simple. A heavy, low velocity gaseous fuel and a light, high velocity gaseous propellant are injected into a reaction chamber having walls composed of some suitable neutron reflecting material. Fissions in the fuel heat the propellant which is then exhausted through a nozzle to give thrust. The gaseous state of the fuel gives the previously mentioned advantage of high temperatures, but also causes a serious problem of fuel separation and containment. Some of the fuel will mix with the propellant and be exhausted from the reactor. In order to maintain a critical fuel mass, additional fuel must be continually injected into the reaction chamber. This is an inefficient use of expensive nuclear fuel which also results in a reduction of specific impulse, due to the increase in the mean mass of the propellant. Several approaches to the fuel containment problem have been proposed. Four of the concepts which have received attention are the vortex flow,


        The plasma core reactor is also referred to as a gaseous core or cavity core reactor.