Time evolution of Kelvin-Helmholtz vortices associated with collisionless shocks in laser produced plasmas
Yasuhiro Kuramitsu1*, Toseo Moritaka1, Michel Koenig2,3, Alexander Pelka2,4, Hideaki Takabe4, Youichi Sakawa5, Akira Mizuta6, Naofumi Ohnishi7
1Department of Physics, National Central University, Jhongli, Taiwan
2LULI, Ecole Polytechnique, Palaiseau, France
3Institute for Academic Initiatives, Osaka University, Suita, Japan
4Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
5ILE, Osaka University, Suita, Japan
6Computational Astrophysics Laboratory, RIKEN, Wako, Japan
7Graduate School of Engineering, Thohoku University, Sendai, Japan
* presenting author:Yasuhiro Kuramitsu, email:yasu@ncu.edu.tw
Kelvin-Helmholtz instability (KHI) is a universal phenomenon in various fluids and plasmas where velocity shears exist. Resultant vortices and turbulences are essential in many space and astrophysical phenomena, as in transport of solar wind to Earth's magnetosphere, and triggered star formation in giant molecular clouds. In space plasmas local variables are obtained by direct measurements with spacecrafts, however, it is difficult to obtain the global structures. Contrary, in astrophysical phenomena the global images are obtained from their emissions, though local observations of physical quantities are inaccessible. Recent rapid growth of laser technologies allows us to model space and astrophysical phenomena in laboratories. Here we report experimental results on KHI and resultant vortices in laser-produced plasmas. By irradiating a double plane target with a laser beam, asymmetric counterstreaming plasmas are created. The interaction of the plasmas with different velocities and densities results in the formation of asymmetric shocks, where the shear flow exists along the contact surface and the KHI is excited. We observe the spatial and temporal evolution of plasmas and shocks with time resolved diagnostics over several shots. Our results clearly show the evolution of transverse fluctuations, wavelike structures and circular features, which are interpreted as the KHI and resultant vortices.
The relevant numerical simulations demonstrate the time evolution of KH vortices and show qualitative agreements with experimental results. Shocks and thus the contact surfaces are ubiquitous in the universe; our experimental results show general consequences where two plasmas interact.


Keywords: Plasmas, Instabilities, Vortices, Turbulence, Laboratory astrophysics