396 / 2019-02-28 17:22:32

Development of high-flux multi-keV X-ray radiators from laser-driven convergent plasma

multi-keV X-ray source; conversion efficiency; convergent plasma

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High-flux multi-keV sources are important for imaging, radiography, X-ray absorption measurements, testing of materials exposed to X-ray radiation, and so on. Improvement of the laser to X-ray conversion efficiency is a common and crucial requirement. Interaction of high intensity lasers with underdense plasma below 0.25 nc has been demonstrated as a effective way to generate high-flux multi-keV X-ray radiator. Underdense plasma ablated from thin wall of a cavity target allows to be further confined and heated. Furthermore, the convergence of the plasma in the cavity is benefit for the transformation of ion kinetic energy to electron internal energy. Consequently, the x-ray conversion efficiency is expected to be substantially increased. Except for the 2-dimention cylindrically convergence, we also tested the 3-dimention spherically convergence. Thin metal and plastic cavities were used in the experiments. The main wall materials of thin metal cavities contain Ti, V and Ni, which are enclosed with CH tubes of 30μm thick to confine the expansion plasmas, and allow the transmission of the X-ray through the encloser. The plastic cavity is a type of chemical compound of chlorine. The K-shell transitions of the cavities between 2keV and 8keV are our aiming emissions. Comparing with traditional solid planer sample, the laser to X-ray conversion efficiency are increased by several times, especially for the spherically convergence mechanism. The characteristics of the X-ray radiator, containing the temporal evolution of the convergent plasma emission, the X-ray spectrum, the hard X-ray yield, and the electron temperature will also be presented.