Study on behaviors of laser produced plumes for fusion material ablation

Summary form only given. Materials used in fusion reactors need to withstand against intense heat, particle, and x-ray fluxes. Those expected values are of 10 to 100 MW/m² at MFE divertor and 10⁹ W/cm² or higher at IFE first walls. Laser ablation scheme can cover such heat flux intensity range and can serve as a heat source at its laser focus spot from 10³ W/cm² to 10¹⁴ W/cm². These intensities cover the ones expected at the divertor (MFE) and the first walls (IFE). The ablation may include plasma, gas, liquid, or solid: all possible phases at an extreme condition where temperature may exceed 1 eV with corresponding densities. The areas of these mixed phases at extreme conditions (MPEC) have not been systematically studied. The inside of the solid wall becomes so called “Warm Dense Matter” where the details of the states should still be clarified. By setting up this laser ablation experiments in a unique way, the ablated plumes can be aligned orthogonally. In this set-up, the plumes ablated from any materials can cross each other and can collide or stagnate. The collision processes include Coulomb, elastic, molecular, and cluster collisions. Those processes were measured with various diagnostics with fast temporal and fine spatial resolutions. Carbon/Carbon plumes show distinctive difference at the stagnation time and the subsequent plume behaviors when observed with a fast frame (50 nsec) camera. In this case the one Carbon plume appears absorbed strongly through the other Carbon plume. The absorption rate reached 60% at laser energy flux of 10 J/cm² or 1.6 E9 W/cm². The experiment was performed at the ablation laser intensity 1E9 W/cm² to 1E10 W/cm² with a laser system at 351 nm wavelength and U energy with 10 Hz repetition rate. The plume temperature and densities can range from 0.1 to a few eV from 1E11 to 1E13 /c.c. The visib- e spectroscopic measurement shows a molecular formation as strong Swan band stemming from the stagnated area especially for Carbon/Carbon plume collisions. The obvious collision and following stagnation indicates the possibility of vapor shielding of incoming heat load flux at the divertor or first wall. We will describe the plume collision and strong stagnation processes in detail and will introduce the capability as an experimental platform for the study of plasma heat load on the fusion wall such as vapor shielding effect with detailed diagnosed data.