Mildly-relativistic shocks are not as well studied as other shock speed regimes like non relativistic shocks in supernova remnants and relativistic shocks in pulsar winds. Because the approximations usually done in relativistic plasma cannot be used, the treatment of mildly relativistic plasma remains under consideration. One important complication is the magnetic field obliquity. Finding the Rankine-Hugoniot jump conditions in mildly-relativistic shocks with an arbitrary obliquity is non-trivial.
There are no analytical approximations and the solution of the full set of MHD equations lead to a system of coupled equations that need to be solved numerically. We have introduced this procedure in the relativistic PIC AMRVAC code. This allows us to perform simulations beyond the state of the art in mildly-relativistic plasma as we combine them with results obtained using pure PIC simulations. The latter provide us with the fraction of particles reflected upstream. The simulations generalize the results obtained in the non-relativistic regime by van Marle et al. (2022). We perform the same kind of parametric survey but in the mildly-relativistic regime including long time 2D simulations, longer than in Crumley et al. (2019).
We have shown that the combination of adiabatic and radiative shocks is of great relevance for enhancing the gamma-ray emission in low velocity shocks in protostellar jets. In Araudo et al. (2021) we have studied, for the first time, the ability of low velocity adiabatic shocks to accelerate protons and amplify the magnetic field through the non-resonant hybrid instabilities. Relativistic protons accelerated in the adiabatic shock diffuse up the dense layer in the contact discontinuity and radiate there more efficiently than in the adiabatic shock downstream region. In del Valle, Araudo, and Suzuki-Vidal (2022) we focused on the instabilities in the contact discontinuity, both in astrophysical and laser plasma.
In a follow up study, and because the poor angular resolution of current and upcoming gamma-ray detectors, we compute the collective emission from all the massive protostars embedded in a single molecular cloud. This study is of great relevance for detectability studies by CTA. (The paper is under preparation.) In addition, by considering low-mass protostars we investigate in deep the injection of low energy cosmic rays in the molecular cloud. Low energy Cosmic Rays are essential to ionize matter at high density column.
Particle acceleration in laser-plasma interactions. Laser plasma shocks are growing in relevance for understanding cosmic rays physics. In particular the injection problem.
Motivated by the experiment performed by Fiuza et al. (2020), where they succeeded in creating a collision-less shock in the laboratory and accelerate electrons up to 500 keV, we are performing a theoretical study of electron acceleration in laser plasma in the same conditions of the experiments in order to shed light on the acceleration mechanism. (Paper in preparation)
