Kelvin-Helmholtz Turbulence Associated with Collisionless Shocks in Laser Produced Plasmas

We report the experimental results of a turbulent electric field driven by Kelvin-Helmholtz instability associated with laser produced collisionless shock waves. By irradiating an aluminum double plane target with a high-power laser, counterstreaming plasma flows are generated. As the consequence of the two plasma interactions, two shock waves and the contact surface are excited. The shock electric field and transverse modulation of the contact surface are observed by proton radiography. Performing hydrodynamic simulations, we reproduce the time evolutions of the reverse shocks and the transverse modulation driven by Kelvin-Helmholtz instability.

Figure 1

Schematic top and side views of the double-foil target and the laser configuration. The transverse diagnostics are interferometry and proton radiography.

Figure 2

Interferograms: (a) before the shot, (b) at 5 ns, and (c) at 8 ns from the main laser. (d) Relevant radiative hydrodynamic simulation at 2 ns: the electron density (upper) and the $x$ component of plasma velocity (lower).

Figure 3

The proton radiograph with $\sim 3\mathrm{MeV}$ protons on the same shot as in Fig. 2c. The time delay of the short pulse laser from the long laser pulse was 8 ns, and the time of flight of the proton is 1.25 ns.

Figure 4

HD simulation shows transverse modulations: (a) the electron number density (upper) and the reduced $x$ component of the electric field (lower) and (b) the $y$ (upper) and $x$ (lower) components of the plasma velocity. (c) Magnified view of a part of (a) where the color scales are modified for aid of view. In the density field, one can clearly see the reverse shock pair and the contact surface. In the electric field, as well as the shock electric fields appearing in the shock front, a turbulent electric field is excited due to the Kelvin-Helmholtz instability.