Observation Of Collisionless-To-Collisional Transition In Colliding Plasma Jets With Optical Thomson Scattering

This paper reports the results of an optical (526.5 nm) Thomson scattering investigation of low-Z (C5H8O2) plasma jets created on the OMEGA laser. We were able to measure the plasma parameters of individual jets and investigate the nature of the interaction when two jets were collided head-on. We found that the mass density of an individual jet increased from 10(-7) to 10(-4) g cm(-3), while the velocity fell from 300 to 100 km s over the probed time period (12-18 ns). When two jets were collided, we were able to capture the transition from collisionless interaction (interpenetration) to collisional interaction (stagnation and shock formation). The timing of the collisionless-to-collisional transition was investigated with visible light self-emission images of the experiments, with streaked Thomson scattering of the interaction region, and by calculating the ion penetration depth based on the measured density and velocity of the jets. All three approaches broadly agree: the colliding jets transitioned from collisionless to collisional behavior around 16 ns after drive laser beams were fired. Published under license by AIP Publishing.