SPRG Seminars
March 3, 2009:
" Cosmic ray acceleration and transport with weak adiabatic focusing"
Reinhard Schlickeiser, Uni. Bochum
Large-scale spatial variations of the guide magnetic field of interplanetary and interstellar plasmas give rise to the adiabatic focusing term in the Fokker-Planck transport equation of cosmic rays. As a consequence of the adiabatic focusing term, the diffusion approximation to cosmic ray transport in the weak focusing limit leads to two new convective transport parallel to the guide field (the well-known focused transport) and in momentum space, respectively. The latter momentum convection represents first-order Fermi acceleration of energetic particles if the product $HL$ of the cross helicity state of Alfvenic turbulence $H$ and the focusing length $L$ is negative.
Besides its formal derivation the basic physical mechanisms for this new acceleration process are clarified and the astrophysical conditions for efficient acceleration are investigated. It is shown that in the interstellar medium this mechanism preferentially accelerates cosmic ray hadrons over 10 orders of magnitude in momentum. Due to heavy Coulomb and ionisation losses at low momenta, injection or preacceleration of particles above the threshold momentum $p_c\simeq 0.17Z^{2/3}$ GeV$/c$ is required.
The imprints of focused transport on the interplanetary propagation of solar flare particles is investigated. It is demonstrated that the measured anisotropy of solar flare particle events provides a powerful diagnostics of interplanetary particle scattering conditions.