Laboratory Simulations of Supernova Shockwave Propagation |
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| Authors: | J F Hansen M J Edwards D Froula G Gregori A Edens T Ditmire |
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| Institution: | (1) Lawrence Livermore National Laboratory, Livermore, CA, USA;(2) University of Texas at Austin, Austin, TX, USA |
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| Abstract: | Supernovae launch spherical shocks into the circumstellar medium (CSM). These shocks have high Mach numbers and may be radiative.
We have created similar shocks in the laboratory by focusing laser pulses onto the tip of a solid pin surrounded by ambient
gas; ablated material from the pin rapidly expands and launches a shock through the surrounding gas. Laser pulses were typically
5 ns in duration with ablative energies ranging from 1–150 J. Shocks in ambient gas pressures of ~1 kPa were observed at spatial
scales of up to 5 cm using optical cameras with schlieren. Emission spectroscopy data were obtained to infer electron temperatures
(< 10 eV).
In this experiment we have observed a new phenomena; at the edge of the radiatively heated gas ahead of the shock, a second
shock forms. The two expanding shocks are simultaneously visible for a time, until the original shock stalls from running
into the heated gas. The second shock remains visible and continues to expand. A minimum condition for the formation of the
second shock is that the original shock is super-critical, i.e., the temperature distribution ahead of the original shock
has an inflexion point. In a non-radiative control experiment the second shock does not form. We hypothesize that a second
shock could form in the astrophysical case, possibly in radiative supernova remnants such as SN1993J, or in shock-CSM interaction. |
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| Keywords: | shock radiative super critical interstellar matter xenon Taylor Sedov Barenblatt Mach |
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