Abstract: A pellet injector for injecting pellets of condensed gas, such as hydrogen, tritium or deuterium, into a reactor comprises an arrangement of pipe guns in a cylindrical arrangement. Each pipe gun which may be made from stainless steel, has a freezing section and three axially spaced metal rings of a heat conductive metal arranged in good thermal contact with the outer surface of the pipe gun at the freezing section thereof. Each of the rings is thermally connected to a cryostat, for example by means of a copper wire. The center ring is cooled to a temperature below the condensing temperature of the gas so as to condense the gas in the freezing section of the pipe gun to form a pellet therein, and the temperature of the adjacent outer rings are maintained at temperatures exceeding the temperature of the center ring so as to obtain a pellet of a desired size. The pellets formed in the pipe guns may be expelled therefrom by a pressurized gas force pulse and injected into a reactor.