Diffusion of Like Particles Across a Magnetic Field

It is shown that the diffusion rate across a magnetic field due to collision of like charged particles is derivable from the macroscopic equations of the plasma. However, it is necessary to include the off-diagonal terms in the stress tensor. The resultant diffusion rate does not obey Fick's law and is proportional to the inverse fourth power of magnetic field strength. This diffusion rate is usually smaller than that due to unlike particle collisions, but may sometimes dominate.