The Essential Requirements of Transition to Non-equilibrium Burn Stage of DD Fuel in Simple Spherical Targets

Abstract

In this research, the transition from equilibrium ignition to non-equilibrium burn is evaluated by calculating the energy balance equations analytically for targets which consist of inner DD fuel and surrounded by a high-Z pusher. It is expected that these targets can trap much of the produced charged particles, radiation or even fast neutrons because of their high-Z pusher. Accordingly, DD fuel can be ignited in volume ignition regime with low ignition temperatures of 35 keV compared to central ignition. Thus, to get a non-equilibrium burning stage, we have examined all the important gain and loss processes for these targets as the energy deposition of fusion products, thermal conduction, radiation flux, mechanical work, bremsstrahlung radiation and inverse Compton scattering as well as competition among them. These conditions have investigated for different areal densities of DD fuel in ρR ~ 1–100 g/cm² and it is shown that as areal density rises, transition temperature decreases. But at high areal densities, the transition temperature does not vary significantly and the limiting temperature of ~ 20 keV will be obtained. Also, transition into non-equilibrium burn is studied for such cases that thermonuclear burn occurs at stagnation moment, before and after that. It is observed that the positive and negative role of mechanical work on the transition conditions is very important and varies transition temperature remarkably. In all cases, transition temperature to non-equilibrium burn phase is always much lower than ideal ignition temperature in specific areal density.