Investigation of the on-axis atom number density in the supersonic gas jet under high gas backing pressure by simulation

Abstract

The supersonic gas jets from conical nozzles are simulated using 2D model. The on-axis atom number density in gas jet is investigated in detail by comparing the simulated densities with the idealized densities of straight streamline model in scaling laws. It is found that the density is generally lower than the idealized one and the deviation between them is mainly dependent on the opening angle of conical nozzle, the nozzle length and the gas backing pressure. The density deviation is then used to discuss the deviation of the equivalent diameter of a conical nozzle from the idealized deq in scaling laws. The investigation on the lateral expansion of gas jet indicates the lateral expansion could be responsible for the behavior of the density deviation. These results could be useful for the estimation of cluster size and the understanding of experimental results in laser-cluster interaction experiments.

The radial dimension of a supersonic jet expansion from conical nozzle

“…Thus it can be concluded that a conical nozzle with a long length and a big opening angle could be helpful to produce a supersonic gas jet with a radially uniform distribution of atom density, especially at a low height. These results can be understood as below: Because the lateral expansion becomes weak with the increase of the nozzle length and the opening angle, 21 it is reasonable that the l H become to be close to l, and the radial distribution tend to be uniform for a nozzle with a long length and a big opening angle at a given height. Meanwhile, as for the height dependence, because the increase of the height results in the TABLE III.…”

“…This results from the fact that the lateral expansion becomes strong as the gas expands from a conical nozzle under the high backing pressure. 21 This fact cannot be explained in the frames of the idealized straight streamline model, since this model provides a fixed structure of the jet for a given nozzle geometry (and a given gas species), which is independent of a gas backing pressure. It is noted that the relation between l T and l H can be obtained using η and η H .…”

“…The dependence of the diameter ratio on these parameters is similar to that of the on-axis atom density on these parameters. 21,22 Due to the lateral expansion, the diameters l, l T and l H are usually different. They tend to be the same only when the conical nozzle with a long nozzle length and a large opening angle is used under a low backing pressure.…”

“…Unfortunately, due to the lateral gas expansion into vacuum, the diameter of a gas jet will be larger than the idealized one. 8,21,22 Thus it is important to know how the lateral gas expansion makes effects on the radial dimension of a supersonic gas jet. In this work, a large number of simulations about supersonic gas jet in case of a conical nozzle with a throat diameter of 0.5 mm were made using the Boldarev's 2D model.…”