Particle-in-cell simulations of laser–plasma interactions at solid densities and relativistic intensities: the role of atomic processes

Abstract

Direct studies of intense laser-solid interactions is still of great challenges, because of the many coupled physical mechanisms, such as direct laser heating, ionization dynamics, collision among charged particles, and electrostatic or electromagnetic instabilities, to name just a few. Here, we present a full particle-in-cell simulation (PIC) framework, which enables us to calculate laser-solid interactions in a "first principle" way, covering almost "all" the coupled physical mechanisms. Apart from the mechanisms above, the numerical self-heating of PIC simulations, which usually appears in solid-density plasmas, is also well controlled by the proposed "layered-density" method. This method can be easily implemented into the state-of-the-art PIC codes. Especially, the electron heating/acceleration at relativistically intense laser-solid interactions in the presence of large scale pre-formed plasmas is re-investigated by this PIC code. Results indicate that collisional damping (even though it is very week) can significantly influence the electron heating/acceleration in front of the target. Furthermore the Bremsstrahlung radiation will be enhanced by 2 ∼ 3 times when the solid is dramatically heated and ionized. For the considered case, where laser is of intensity 10 20 W/cm 2 and pre-plasma in front of the solid target is of scale-length 10 µm, collision damping coupled with ionization dynamics and Bremsstrahlung radiations is shown to lower the "cut-off" electron energy by 25%. In addition, the resistive electromagnetic fields due to Ohmic-heating also play a non-ignorable role and must be included in realistic laser-solid interactions.

Observation of a high degree of stopping for laser-accelerated intense proton beams in dense ionized matter

“…We used the recently developed PIC code LAPINS 79 , 80 , which is able to simulate intense beam-plasma interaction in a self-consistent way, which contains both close collisions and collective electromagnetic fields (see details in “Methods”). The simulation assumes, the incident proton beam to have Gaussian distribution in space and time, with a beam duration of 1 ps and a transverse extension of 1 mm.…”

Ionization-induced laser-driven QED cascade in noble gases

“…The contribution of the collisional ionization can be also estimated by similar way. The cross-section of the collisional ionization for the relativistic electrons is σ ci 2 7/2 π 1/2 /3 Z 2 α·r 2 e L, where L is the Coulomb logarithm [38]. Even for very large value of L = 20 the number of electrons produced via collisional ionization N e,ci = n e N i cσ ci τ c 0.016 is much less than the number of the electrons created via field ionization N e N i > 10 4 in the cascade volume.…”

The self-focusing condition of a charged particle beam in a resistive plasma

“…To confirm the above theoretical predictions, we have used LAPINS code (Chen et al 2020;Ren et al 2020;Wu et al 2018Wu et al , 2020 to make multiple sets of 2D3V simulations of a proton beam propagating in a uniform large-scale hydrogen plasma. As we know for typical particle-in-cell (PIC) simulations, the plasma frequency needs to be resolved, and moreover the grid size must be comparable to the Debye length to minimize artificial In the 30 sets of simulations run by LAPINS code, the values of the proton beam density (in units of n 0 ) and velocity (in units of the light speed c ≈ 3.0 × 10 8 m s −1 ).…”