Particle acceleration


    Energetic ions and electrons in space are deflected by electromagnetic fields. In a homogenous magnetic field that leads to helical motion, and fluctuations in the magnetic field can modify the pattern of that motion, but will not change the energy of the particle.
    Particle acceleration requires an electric field. We investigate three processes that involve electric fields and lead to particle acceleration. At cosmic shocks, that are found in essentially all outflow sources, the systematic difference in flow speed on the two sides of the shock leads to systematic acceleration that is akin to the acceleration of a tennis ball bouncing off a moving racket.
    Turbulence in space provides fluctuating electric fields that can accelerate particles in a statistical manner, as some particles gain energy and some (fewer) lose energy. Often, this so-called stochastic acceleration re-accelerate electrons and ions that received their first boost in energy through other processes.
    Magnetic reconnection destroys magnetic fields, but can lead to an electric field that efficiently accelerates electrons and ions. This process is particularly effective, where the magnetic field is initially strong, such as on the surface of the sun.


    Acceleration at the outer shock of a supernova remnant and the subsequent transport of high-energy electrons shape the intensity distribution of high-energy gamma rays, here for a supernova remnant at the age of 500 years.