Parallel heat flux from low to high parallel temperature along a magnetic field line

In a long mean-free-path plasma where temperature anisotropy can be sustained, the parallel heat flux has two components with one associated with the parallel thermal energy and the other with the perpendicular thermal energy. In a kinetic simulation with magnetic flux expansion toward an absorbing boundary, the parallel heat flux of the parallel thermal energy is found to flow from a low to high parallel temperature region. This unusual behavior is understood with the help of an analytical calculation of the drift-kinetic model using the same upstream source in the simulation.