A study of one-dimensional colliding laser-produced plasmas through modeling and experimentation

Abstract

An investigation was conducted into two colliding laser-produced plasmas collimated by two face-to-face channels, which makes the plasmas close to one-dimensional (1-D) and thus easier to simulate. The study was carried out using time-resolved imaging, and a 1-D fluid-descriptive model with the ambipolar electric field and collisional coupling taken into account. The time-resolved images show that the 1-D colliding plasmas follow a division into three distinct periods, namely, pre-colliding, colliding, and finally the stagnation layer dissipating. In the pre-colliding period, there is no plasma coming out of the channels, but illumination features are observed near the inner surfaces of the two blocks for more than 150 ns, which is much longer than the laser pulse duration. In the colliding period, there is continuous ejection of plasma from the channels and the formation of a stagnation layer due to the collision of the two plasmas. The dissipation of the stagnation layer into its nearby space in the third stage can be clearly observed in the images. Applying the 1-D model, the simulation results predict the temperature spikes and density increase in the layer due to the conversion of the macro-kinetic energy of the plasmas into their internal energy with the flow velocities almost vanishing. The ratios of the ion–ion mean-free-path to the characteristic length at the midpoint of the two plasmas, extracted from the simulation, indicate that the stagnation layer is a soft one with partial plasma interpenetration through the interface between the two plasmas.