Self-Navigation of Laser Drivers on Injected IFE Direct Drive Pellets

Full text: There are many serious obstacles complicating the classical direct drive IFE scheme -even putting in doubts its practical feasibility. Among the most serious ones is the insufficient predictability of the injected pellets' trajectories resulting from their expected interactions with remnants of previous fusion explosions due to the considered 5-10 Hz repetition rate. This is one of the reasons why the indirect drive scheme -despite its higher demand on laser energy -seems to be currently considered a more serious IFE candidate. The corresponding hohlraum targets are by three orders of magnitude heavier compared to their direct drive counterparts thus allowing for more reliable prediction of their trajectories. In this contribution a recent progress achieved in the stimulated Brillouin scattering (SBS) phase conjugating mirror (PCM) based inertial fusion energy (IFE) approach proposed recently as an alternative to the IFE classical approach mentioned above will be presented. By taking care of automatic self-navigation of every individual laser beam on injected pellets with no need for any final optics adjustment this technology is of particular importance to the direct drive scheme. Conceptual design of one typical laser driver will be shown and its features discussed. This approach would allow for higher number of laser drivers to be employed. Operating with lower energies (∼ 1 kJ - thus avoiding the optics damage caused by perpendicular SBS) such laser drivers would be easier to design for the required repetition rate. In comparison with the earlier design an upgraded scheme was developed with the low energy illumination laser beam entering the reactor chamber through the same entrance window as used by the corresponding high energy irradiation laser beam. The pellet survival conditions in the period between its low energy illumination and subsequent high energy irradiation were studied and upper limits on the energies absorbed after their illumination for both DD and DT fuels were found. Results of experimental verification of this improved design will be reported. In these experiments for the first time a complete setup including the pellet (realized by the static steel ball) was employed. This concept of self-navigation should be, in principle, applicable also to direct drive targets with cones. (author)