Energy transfer processes in burning fusion plasmas

Summary form only given. Creation of a burning plasma that is heated by α-particles created in fusion reactions, is of great importance for successful inertial fusion experiments. In order to model the initiation and propagation of a burn wave through the fusion fuel, it is vital to have a good understanding of the energetics involved. Only through correct modeling can improvements in experiment including ignition and sufficient burn be achieved within the strict constraints imposed on driver energy and confinement time. In this contribution, simulations are shown that investigate the initiation of the burn wave in an inertial fusion reactor and the energy transfer processes which govern its dynamics. Energy deposition profiles of fusion α-particles are calculated, including degeneracy effects, using several stopping power formulae. Electron-ion energy transfer within the fuel is described using a coupled mode model that incorporates collective effects and arbitrary degeneracy. Quantum statistically based equations of states are then employed to determine heat capacities of the electron and ion populations. Results of the simulation can be used to imply limits on α-particle flux and hot spot size necessary to burn a sufficient quantity of the fuel. To highlight the significance of the dense-plasma effects involved, the simulation results are compared using differing models. In cooler, denser plasma regions, which exhibit high levels of degeneracy in their electron systems, large discrepancies can be seen between stopping power models that sufficiently describe this effect and those obtained within classical physics. In burning plasma regions, i.e. regions of low electron degeneracy, the choice of stopping power model does not have such a large effect on the calculated energy deposition. However, these differences are significant in post-compression fuel and, thus, are important in modeling the initiation and propagation of an α-parti- le burn wave. Our simulations show that, depending on the α-flux, either the energy deposition of the α-particles or the electron-ion equilibration sets the time taken for a given fuel layer to start to burn. This gives the speed of the burn wave.