Low gain (Q ~ 1) fusion plasma systems are of interest for concepts of fusion–fission hybrid reactors. Operational regimes of large modern tokamaks are close to Q ≈ 1. Therefore, they can be considered as prototypes of neutron sources for fusion–fission hybrids. Powerful neutral beam injection (NBI) can support the essential population of fast particles compared with the Maxwellial population. In such two-component plasma, fusion reaction rate is higher than for Maxwellian plasma. Increased reaction rate allows the development of relatively small-size and relatively inexpensive neutron sources. Possible operating regimes of the NBI-heated tokamak neutron source are discussed. In a relatively compact device, the predictions of physics of two-component fusion plasma have some volatility that causes taking into account variations of the operational parameters. Consequent parameter ranges are studied. The feasibility of regimes with Q ≈ 1 is shown for the relatively small and low-power system. The effect of NBI fraction in total heating power is analyzed.
From pure fusion to fusion–fission Demo tokamaks