Studies of turbulent liquid sheets for protecting IFE reactor chamber first walls

Abstract The HYLIFE-II conceptual inertial fusion energy (IFE) reactor design uses stationary and oscillating slab jets, or liquid sheets, to create a protective pocket that allows target injection and driver beam propagation while protecting the chamber first walls from neutrons, X-rays and target debris. Thick liquid wall protection can, therefore, reduce reactor chamber size and increase chamber lifetime in commercial IFE reactors. Minimizing driver beam interference and irradiation of the final focus magnets places stringent requirements upon the surface smoothness of the stationary liquid sheets that shield the heavy-ion driver array. Experiments were carried out to determine how nozzle and flow conditioner design affect surface smoothness in turbulent liquid sheets at Reynolds numbers up to 130 000. The free-surface was directly imaged using planar laser-induced fluorescence (PLIF) at downstream distances up to 25 times the sheet thickness at the nozzle exit. The data are processed to determine the probability of finding fluid at any given spatial location. The surface smoothness of sheets of water issuing from nozzles with various contractions and rectangular or nearly elliptical exits into atmospheric pressure air were quantified and compared. The free-surface characteristics of liquid sheets issuing from unblocked and partially blocked (2.5% of total area) but otherwise identical flow conditioners were compared to investigate the robustness of flow conditioning elements over long operation times. These results on nearly prototypical turbulent stationary liquid sheets address a number of technical feasibility issues for thick liquid protection in IFE reactors.