Spatio-temporal evolution of laser ablation W plasma under low-pressure Ar gas and Ar plasma ambients†

Abstract

Understanding the spatio-temporal evolution of laser ablation plasma under low-pressure ambients is a crucial area of study in the field of laser-induced breakdown spectroscopy (LIBS). In this work, LIBS combined with plasma imaging was employed to diagnose the spatio-temporal evolution of laser ablation W plasma under Ar gas ambient and continuous Ar plasma ambient with low-pressure conditions. Results revealed that laser ablation W plasma under Ar plasma ambient exhibited high radiative recombination loss and radiative thermal bremsstrahlung loss in the early stages of spatio-temporal evolution. This led to an increased continuous radiation background and W II signal intensity. It was found that the electron temperature initially exhibited a brief decline, followed by an increase, and then decreased gradually. This resulted in a temporary temperature drop caused by the inertia of plasma expansion, which was quickly compensated by the recompression of the shockwave layer. Plasma imaging results revealed plume splitting, plume sharpening, and plume turbulence in laser ablation W plasma under Ar gas ambient. The front position and area of the plasma plume under Ar gas ambient and Ar plasma ambient were compared. In the later stages of temporal evolution, the plume area of the plasma could be described using a drag model. Thus, this study provides new insights into the physical mechanisms of laser ablation W plasma under different background ambients, which is important for the real-time diagnostics of wall materials by LIBS during tokamak discharges.