If the x-ray emission always exceeds the total thermonuclear power, the plasmoid will not heat up fast enough to burn most of the fuel. Unless most of the fuel is burned up, the output energy from the plasmoid will not exceed the input energy, so net energy production will not be possible. The magentic field effect reduces the -ray emission sufficiently that the plasmoid heats up to a peak tempearture of aroudn 700-900keV and 80% or more of the fuel is burned, producing net energy.