- 166 -


when temperature distributions are calculated from equation (8.49). These temperature distributions, T(r), and the plasma pressure and mixing ratio determine the values of C (r) and Ci (r), from which the bremsstrahlung energy loss
e1
is calculated from (8.63). From equation (8.62), the fission fragment energy necessary to support the calculated temperature distribution is

               S  (r) = S(r) + B(r)                (8.64)
               ff


        The fission fragment power density, and the net

power density available for heating the plasma to a given centerline temperature are shown in Figure 23. The energy production is based on a fission fragment energy of 165 Mev/fission. As in the case of fusion devices, the bremsstrahlung energy loss in a fission plasma constitutes a substantial obstacle to the prolonged steady state operation at elevated temperatures. Without considering the problems of plasma instabilities and radiant energy transfer, the physical limitation to the plasma reactor's performance will probably be the achievement of a fission fragment power density which is sufficient to offset bremsstrahlung losses. This high fission fragment power density can only be realized by maintaining the reactor on a positive period until the desired fission density is reached. If the increase from low power to the required