Laboratory Simulation of the Structure of Jets from Young Stars

We present the results of laboratory simulation of jets from young stars at the PF-3 plasma focus facility at the NRC "Kurchatov Institute." The objective of research question was to determine factors making the spatial structure of plasma jets in discharges in gases of different chemical compositions, namely, neon, helium, and helium with admixtures of neon, different. It was found that the plasma flow in the case of pure neon is the most structured: the head of the ejection consisted of numerous clumps, which makes is very similar to clumps in the jets from young stars, the so-called Herbig-Haro objects. The ejection in the case of pure helium was the least structured. However, the shape of the ejection head substantially changes upon admixing merely 1% of neon into helium, revealing a noticeable small-scale structure. Estimates show that these specific features can be related to the difference in the cooling efficiency of the studied gases both in the plasma ejection itself and in the shock wave generated upon jet propagation through the background gas. It is suggested that the main reason for the appearance of inhomogeneities in the plasma blob are different types of instabilities that develop in the presence of efficient radiative cooling, as is the case of the Herbig-Haro objects. In addition, it was established that, in some cases, plasma ejections can consist of several blobs propagating nearly parallel to each other that appear as early as at the stage of plasma pinching. Collision of shock waves generated by each of the blobs leads to the appearance of clumps, which facilitates formation of the lace-like structure of plasma ejection.