Challenge for continuous operation of extreme ultra-violet light source using hypersonic jet

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In order to make a controllable beam target, a hyper-sonic localized jet was formed quasi-continuously in vacuum. An apparatus composed of a miniature Laval nozzle, a gas target chamber, and a supersonic diffuser was constructed for studies on the gas target formation and the gas-dynamical study on the nozzle and diffuser flows. Results showed, for continuous operation of the free-jet flow, diffuser optimization is critically important. We measured static pressure profiles in the supersonic nozzle as a function of the stagnation pressure and the nozzle geometry, which indicated effects of non-equilibrium condensation on the pressure profiles. We proposed a semi-empirical method to predict the nucleation and cluster formation processes based on the nozzle flow experiments and a numerical model considering the condensation process. The model could characterize the supersaturated states and onset of the condensation from the pressure profiles of the non-equilibrium condensation flow.