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Electromagnetic turbulence and collisionless shock in astrophysical counter-streaming plasmas hold great significance in field amplification and cosmic particle acceleration. In the past decade or so, the laser-driven counter-steaming plasma experiments (such as NIF and OMEGA platforms) successfully observed the magnetic field generation, collisionless shock, and particle energization. However, the underlying physics about the effects of electromagnetic turbulence and collisionless shock on ion kinetics and neutron generation remains largely ambiguous, which is because laboratory-scale full particle-in-cell (PIC) simulation including plasma instabilities, collisional thermalization, and neutron diagnosis is challenging for the laboratory astrophysics community. We report a full kinetic numerical and theoretical study of electromagnetic turbulence, perpendicular shock, and ion energization by utilizing a recently developed high-order implicit PIC code with realistic laboratory conditions. It is shown that the electromagnetic turbulence is driven by plasma instabilities. When the interpenetrating plasmas are immersed a magnetic field of tens of Tesla, the growth rates of instabilities increase with the strengthening of applied magnetic field, which therefore leads to a significant turbulent field amplification. Ion distribution function shows a distinct super-Gaussian shape under the competition between the stochastic acceleration due to electromagnetic turbulence and collisional thermalization. For the scenarios where premagnetized occurs prior to the interaction of the two plasma flows, PIC simulations show that a supercritical perpendicular collisionless shock is formed when two premagnetized flows collide, in which ions, regardless of whether they pass through or are reflected by the shock, can gain energy by the shock surfing acceleration (SSA). Furthermore, the ion kinetics are manifested in neutron diagnostics. Our results have well explained the recent unmagnetized experimental observations. This work has important implications for field amplification and high-energy cosmic particle generation in astrophysical counter-streaming systems.
Peng Liu is a PhD candidate of Institute for Fusion Theory and Simulation in Zhejiang University. He is engaged in the theories and numerical simulations of laser-plasma interaction. Currently, his main research interests focus on electromagnetic turbulence and collisionless shock associated with laboratory astrophysics.
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