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News of February

2D jets at PALS

In the last ten years a number of laboratory experiments on high-power lasers have been developed to study high-Mach number jets. Although laser produced jets have generally required energies in the kJ range, it was recently shown by Kasperczuk et al. 2006 that direct irradiation of a massive metal target with smaller laser energies (less than few hundred J) can produce collimated, jets in the correct scaling regime. We present simulations of a variant of this jet generation mechanism, which results in the formation of slab-jets with laser energies of about 30 J. Beside the low energy required, these slab-jets are interesting because of their reduced geometry, essentially two-dimensional, which makes them easier to diagnose and simulate. The experiments were carried out at the PALS laser facility with a beam energy in the range ~ 30 J and a pulse duration of 300 ps (at 1.315 &mu m), irradiating a planar massive target consisting of an iron foil. The laser focal spot consists of two parallel strips stretched (~ 1 mm) in the x-direction. Their intensities (~ 1.6 1013 W/cm2) along the y-direction have nearly Gaussian distributions (FWHM of 100 &mu m) and the peaks are separated by ~ 400 &mu m. The simulations, performed with the GORGON code, indicate a Mach number of 5, which may reach a 30 by increasing the laser intensity by a factor of 5 with the same focal spot geometry. Such 2D jets may be useful to develop tests for 2D numerical simulations and to develop experiments aimed at addressing instabilities (e.g. Kelvin-Helmoltz) linked to the propagation of radiatively cooled jets in the ISM. These results are presented in our recent paper, which also address the question of scaling in the context of stellar jets.

Figure 1 : XUV image of the experimental jet.


" Scaling stellar jets to the laboratory: the power of simulations"
C. Stehlé, A. Ciardi, J.P. Colombier, M. Gonzalez, T. Lanz, A. Marocchino, M. Kozlova, M., B. Rus,
arXiv:0912.4279 (2009), Laser and Particle Beams (2009), 27,issue 4,709-717 Reprint

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