  Based on the rate of expansion of the solar wind, the plasma should cool
rapidly as a function of distance to the Sun. Observations show this is not the
case. In this work, a magnetic pumping model is developed as a possible
explanation for the heating and the generation of power-law distribution
functions observed in the solar wind plasma. Most previous studies in this area
focus on the role that the dissipation of turbulent energy on microscopic
kinetic scales plays in the overall heating of the plasma. However, with
magnetic pumping particles are energized by the largest scale turbulent
fluctuations, thus bypassing the energy cascade. In contrast to other models,
we include the pressure anisotropy term, providing a channel for the large
scale fluctuations to heat the plasma directly. In this work a complete set of
coupled differential equations describing the evolution, and energization, of
the distribution function are derived, as well as an approximate closed form
solution. Numerical simulations using the VPIC kinetic code are applied to
verify the model's analytical predictions. The results of the model for
realistic solar wind scenario are computed, where thermal streaming of
particles are important for generating a phase shift between the magnetic
perturbations and the pressure anisotropy. In turn, averaged over a pump cycle,
the phase shift permits mechanical work to be converted directly to heat in the
plasma. The results of this scenario show that magnetic pumping may account for
a significant portion of the solar wind energization.
