The Acceleration of Charged Particles at Collisionless Shocks in Space and
Astrophysics

The acceleration of charged particles to the highest energies ever measured (~10**20 eV ) occurs in Astrophysical settings. How this happen is still not fully understood. It is believed by many that the diffusive
shock acceleration mechanisms is the key to this puzzle because it naturally produces a power law for the accelerated charged particle spectrum over a wide range of energies as observations show. However,
radiation measurements from remote astrophysical shocks such as supernovae remnants can take us only so far in figuring out the details of shock acceleration since the radiation is produced by the shock accelerated
particles and we do not see these particles directly. With the discovery of the termination shock around the Sun in the solar system plasma when the Voyager 1 and 2 space craft crossed it in 2004 and 2007, we have
detailed direct measurements of charged particles accelerated by a large-scale collisionless shock and about the shock itself. We will discuss how the Voyager observations challenge us to come up with a more
sophisticated model for charged particle shock acceleration at quasi-perpendicular shocks, which in some ways are not as well understood as at quasi-parallel shocks.

Jakobus A. le Roux

UAHuntsville