Dynamics of the heat flux-induced ion turbulence in a laser-produced plasma

A self-consistent determination of the ion turbulence level in a laser-heated, expanding plasma, has been done with an inhomogeneous, hydrodynamic model. It is shown for one μm radiation, that the heat flux-induced ion turbulence appears only for laser pulse intensities≳1014 W cm−2, with rise times ≲100 psec, for plasmas with Z≳5. When present, this ion turbulence is space and time dependent. It has a short lifetime (for instance 50 psec for Z=10), and it is confined only in the conduction region, where transport inhibition is f*e∼0.2. There is no enhancement of absorption, because convecting ion modes are strongly Landau-damped before reaching the critical density nc. On the other hand, a strong enhancement of absorption is found when suprathermal electrons are present: In that case, the suprathermal energy flux towards the dense plasma substantially raises the turbulence level near nc, and strongly increases the absorption of laser energy by inverse bremsstrahlung.