Beam Instabilities in Laser-Plasma Interaction: Relevance to Preferential Ion Heating

We propose a new mechanism for anomalous ion heating in ultraintense laser plasmas. This mechanism is based on the excitation of an electron two-stream instability that is driven by the fast electron beam that resonantly decays into ion-acoustic waves. These low frequency waves are then strongly damped by the ion collisions in the dense plasma. The model gives a simple explanation for the preferential heating of the bulk ion population observed in recent laser experiments in the petawatt regime. In particular, this work provides an explanation for the different energy loss in the Au and CD plasmas, in cone-guided fast ignition experiments.