Ion acoustic instability driven by a temperature gradient in laser-produced plasmas

The return current instability excited in laser-produced plasmas by a temperature gradient has been studied using a nonlocal theory of electron transport. The transport model is applicable for an arbitrary ratio of the temperature inhomogeneity scale length to the collisional mean free path. It is demonstrated that nonlocal thermal effects have a significant impact on the ion acoustic instability growth rate, threshold and angular distribution of excited waves that can be important for the interaction of smoothed laser beams with a plasma. A nonlinear dependence of the return current instability growth rate on the gradient length has been discovered. The particularly important example of ion acoustic instability due to inhomogeneous plasma heating as a result of inverse bremsstrahlung absorption in a hot spot has been considered.