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news:particle_acceleration_in_mildly_relativistic_plasmas [2016/11/07 14:26] (current)
monikamo created
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 +Astrophysics Colloquium
  
 +Tuesday 8 November 2016  -  HG00.071 - 16.00 h.
 +
 +Patrick Crumley
 +(The Anton Pannekoek Instituut for Astronomy of the Univ. of Amsterdam)
 +
 +
 +"​Particle Acceleration in Mildly Relativistic Plasmas"​
 +
 +Shocks waves are ubiquitous in astrophysical plasmas, occurring whenever a
 +pressure-driven disturbance travels through a fluid faster than the signal
 +speed of the fluid. In astrophysical plasmas, nearly all shocks have 
 +widths far smaller than the mean free paths of the constituent particles ​
 +of the plasma, meaning that the shock is collisionless. Collisionless ​
 +shocks are capable of accelerating particles to high energies, although ​
 +the acceleration mechanism is not yet understood from first principles. ​
 +The main candidate for accelerating particles in shocks is diffusive shock 
 +acceleration (DSA), where particles gyrate around the shock front, ​
 +diffusively scattering off turbulent fields, and gaining energy from the 
 +converging flows. I will discuss the physics of particle acceleration in 
 +shocks in a regime largely ignored in the literature,
 +the transition between relativistic and Newtonian shocks. There are many
 +astrophysical sources that are thought to have shocks with mildly ​
 +relativistic velocities: AGN, X-ray binaries, and late-time GRB 
 +afterglows. In addition, the mildly relativistic regime is a place where 
 +we expect the microphysics of collisionless shocks to be changing. ​
 +Studying these shocks self-consistently requires a methodology that is 
 +capable of allowing the particles in the plasma to generate and interact ​
 +with electromagnetic fields. Particle-in-cell (PIC) simulations are an 
 +ideal tool study how collisionless shocks change as they transition ​
 +between relativistic and Newtonian regime. I will present preliminary ​
 +results of PIC simulations of mildly relativistic shocks that show
 +non-thermal acceleration in both electrons and ions.