Plasma microphysics of particle acceleration at oblique shocks

• Applicant: Dr. Naveen Kumar
• Subject Area: Astrophysics and Astronomy ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 522551585

The origin and acceleration of cosmic rays in the Universe remains an open question despite more than a century after their first discovery and it remains one of the central problems of high-energy astrophysics and astro-particle physics. It is commonly accepted that cosmic rays are primarily accelerated by a Fermi-type process known as diffusive shock acceleration at astrophysical sites such as the external collisionless non-relativistic shocks of supernova remnants. Current theoretical and numerical modelling of cosmic-ray acceleration primarily consider magnetic field obliquity i.e. the angle between the upstream magnetic field and shock normal direction, to be lower than 45 degree, so-called quasi-parallel shocks. However, for several different astrophysical scenarios a broad range of magnetic field obliquities is expected over a large surface area of the shock. Until recently, it has been argued in the literature that the hadronic component of particle acceleration by shocks is strongly favored only below a fixed range of the magnetic field obliquity. In this project, I will study particle acceleration (electrons and ions) and critically evaluate the dependence of ion acceleration and its efficiency on magnetic field obliquities claimed before in the literature. I will extend my recent large-scale 1D3V (one spatial and three velocity dimensions) PIC simulations to multi-dimensional geometry as only kinetic simulations can self-consistently capture the plasma microphysics involved in the onset of particle acceleration at shocks. My current results have challenged the currently accepted paradigm which argues that ion acceleration and its efficiency severely suffer at high magnetic field obliquities. I expect the results to significantly advance our understanding of non-thermal particle acceleration and radiation generation at non-relativistic oblique shocks.

• DFG Programme: Research Grants