Characteristic of spatiotemporal evolution of hydrogen isotope in laser-induced plasma under low-pressure environment

Abstract

The elemental analysis of hydrogen (H) and its isotopes, deuterium (D) and tritium (T) is important for fuel retention detections in plasma-facing materials of nuclear fusion devices, H abundance assessment in geochemistry and so on. Laser-induced breakdown spectroscopy (LIBS) is one of the most promising technology to analyze the H isotopes due to its excellent real-time and in situ analytical ability. However, the laser ablation plasma is a transient plasma with inhomogeneous spatiotemporal evolution. Especially in low-pressure background, the particles with different masses may separate in the plasma plume. This will result in the loss of accuracy of LIBS measurement. In this work, the characteristic of spatiotemporal evolution of spectra from laser-induced plasma on the frozen D2O-H2O mixture under low-pressure environment has been investigated. The spectral intensity of Dα and electron density decrease with radial direction and delay time. The intensities ratio of Dα and Hα, ID/(ID + IH), are almost constant at different radial positions and delay times under the background pressure of 1 × 10−1 mbar. However, when the pressure decreases to 1 × 10−4 mbar, ID/(ID + IH) decreases from the center to the edge of the plasma due to plume separation by the different atomic masses of isotopes. The degree of separation increases from the center to the edge of the plasma. The results will be useful for better understanding of characteristic of spatiotemporal evolution of LIBS plasma in low pressure and improvement of LIBS measurement for H isotopes.