New cosmic ray transport effects from the mirror force in inhomogeneous magnetic fields

• Applicant: Professor Dr. Reinhard Schlickeiser
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 248902482

• Final Report Year: 2017

Final Report Abstract

With the availability of the AMS-02 data and Voyager-I, measuring for the first time interstellar cosmic ray spectra at kinetic energies below 1 GeV/Nucl., cosmic ray physics has entered a new high-precision era. Contrasting these high-precision data with correct theories of cosmic-ray transport and acceleration is an urgent challenge for future research. With our project we contributed to a more accurate theory of cosmic ray transport and acceleration. Besides the well-known effect of adiabatic focusing on spatial particle transport, the mirror force in inhomogeneous guide magnetic fields gives rise to focused acceleration of particles in plasma wave turbulence with a net nonzero cross helicity state of Alfven waves Hc = 0, which is a first-order Fermi type particle acceleration process. In order to accelerate cosmic ray particles by focused acceleration its acceleration rate has to be greater than the continuous energy loss rate and the catastrophic fragmentation loss rate of cosmic rays. We calculated anew the energy loss rate from pion production in inelastic hadron-hadron collisions, establishing a break in the energy loss rate at about 200 GeV which leads to a corresponding hardening by E 0.2 from low to high energies in the differential energy spectra in excellent agreement with observations. A non-zero value of the cross helicity Hc = 0 is essential for the occurrence of focused acceleration. We showed that degenerated cross helicity values Hc = ±1 result when cosmic rays penetrate interstellar molecular clouds. Nonrelativistic cosmic rays inside MCs lose energy by ionizing and heating the molecular gas at small penetration depths of about Z1 = 2.33 pc, whereas at large penetration depths Z > Z1 they are collectively dissipated by the streaming instability. Molecular clouds with thicknesses greater than Z1 are an efficient sink of nonrelativistic cosmic rays. One half of the energy density of incoming interstellar nonrelativistic cosmic rays is converted into degenerated Alfvenic wave turbulence by the streaming instability at large penetration depths. Therefore the interior of giant molecular clouds seems to be an ideal site for efficient focused acceleration of nonrelativistic cosmic rays. The telegraph approximation for particle transport is systematically developed in the presence of boundaries, taking into account the adiabatic focusing effect in a non-uniform mean magnetic field. We derived reflecting and absorbing boundary conditions for a modified telegraph equation with a convective term, and presented analytical solutions of illustrative boundary problems. The accuracy of the telegraph approximation for focused transport in the presence of boundaries is demonstrated by comparing the analytical solutions of the telegraph approximation with the numerical solutions of the original Fokker-Planck equation.

Publications

• Modification of the parallel scattering mean free path in the presence of adiabatic focusing, Astrophys. J. 792 (2014) 85
  He, H.-Q. and Schlickeiser, R.
  
• Cosmic ray transport in astrophysical plasmas, Phys. of Plasmas 22 (2015) 091502
  Schlickeiser, R
  
• Diffusive cosmic ray acceleration at relativistic shock waves with magnetostatic turbulence, Astrophys. J. 809 (2015) 124
  Schlickeiser, R.
  
• Explanation of the spectral hardening of relativistic galactic cosmic ray protons, Astrophys. J. 811 (2015) 11
  Krakau, S. and Schlickeiser, R.
  
• Effects of latitudinally dependent solar wind speed on diffusion coefficients of cosmic rays in the presence of adiabatic focusing, Astrophys. J. 800 (2015) 117
  He, H.-Q. and Schlickeiser, R.
  
• Pion production momentum loss of cosmic ray hadrons, Astrophys. J. 802 (2015) 114
  Krakau, S. and Schlickeiser, R.
  
• The telegraph approximation for focused cosmic-ray transport in the presence of boundaries , Astrophys. J. 806 (2015) 217
  Litvinenko, Y. E., Effenberger, F. and Schlickeiser, R.
  
• Cosmic rays and MHD turbulence generation in interstellar giant molecular clouds, Astrophys. J. 824 (2016) 89
  Schlickeiser, R., Caglar, M. and Lazarian, A.