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LULI2000 - Generation and stability of ion phase-space holes in counter-streaming plasma flows and their relation to the two-streaming instability (L. Romagnani)

Several different nonlinear processes and instabilities can be generated in the interaction of high-­‐power laser pulses with plasmas. Among these two-­‐stream instabilities can grow in the collisionless interaction between counter-­‐streaming, laser-­‐ generated plasma flows. Phase-­‐Space Holes are resilient coherent structures that can be regarded as nonlinear saturated states of these two-­‐stream instabilities. They belong to a class of “preferred” electrostatic BGK modes (including Electron and Ion Phase-­‐Space Holes and Double-­‐Layers) which, provided that the excitation mechanism is strong enough, inevitably grow from the linear stage of the instability, in turn affecting the whole plasma dynamics. Phase-­‐Space Holes and Double-­‐Layers are of relevance to a number of different astrophysical scenarios. Satellite observations have found evidence of their existence in the Earth auroral region, where they appear to contribute to the acceleration of energetic ions and electrons. We propose to perform experimental investigations to study the generation and stability of Ion Phase-­‐Space Holes, and their relation to the two-­‐stream instability, in laser-­‐generated counter-­‐streaming plasma flows. In the experiment modulations associated with the growth of the instability and with the generation of the phase-­‐space holes will be detected via proton-­‐probing measurements of the associated electric fields. A novel streaked proton probing technique will be combined with standard proton-­‐projection imaging, allowing for a nearly continuous temporal resolution of the plasma evolution. These techniques will be complemented by optical interferometry and Thomson scattering measurements, which will allow a full characterization of the relevant plasma parameters.

LULI2000 - S15-17/2019