The physical basis for numerical fluid simulations in laser fusion

A review of the physical basis for the numerical fluid simulation of a large class of laser fusion experiments and of related physics issues is presented. The main emphasis is on processes relevant to the description of the direct-drive approach, employing moderate intensity, short wavelength laser pulses. The rationale for the use of fluid models, and for several simplifications of the resulting MHD equations is addressed with some details. The relevant atomic physics modeling is discussed in connection with the peculiar density-temperature range of laser fusion experiments. Models for the transport of radiation, suprathermal charged particles and neutrons, as well as for laser-matter interaction, are reviewed. A brief survey is also given of the main laser fusion codes. A survey of selected applications of fluid codes to 'model problems' of particular physical aspects of laser fusion, to the simulation of present experiments, and to the design of reactor-size targets is then presented. It is concluded that the basic physical modeling employed by state-of-the-art fluid codes seems to be adequate to the simulation of the class of experiments of interest, as well as to the overall target design. Indeed, results of experiments that are not dominated by fluid instabilities are simulated quite satisfactorily. Also, 2-D simulations have allowed for the first quantitative studies of several fluid instabilities, as well as of the effects of large scale-length non-uniform irradiation. Great progress is instead still needed to perform detailed multi-dimensional simulations capable of dealing simultaneously and self-consistently with both short and large scale-length perturbations.