Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jets winds etc.) is a common process which leads to a more intricate structure of the Interstellar medium (ISM). In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNR) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage and the distance between the two stars. In this letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BW) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼ 500 J) of 300 µm diameter carbon rods and propagate in different gases (Ar and N) at different pressures. The physical parameters, such as density and temperature of the IR are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17-20 % increase of temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long times after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect.