  Kinetic effects in plasma flow due to a finite ion temperature and ion
reflections in a converging-diverging magnetic nozzle are investigated with
collisionless quasineutral hybrid simulations with kinetic ions and isothermal
Boltzmann electrons. It is shown that in the cold ions limit the velocity
profile of the particles agrees well with the analytical theory predicting the
formation of the global accelerating potential due to the magnetic mirror with
the maximum of the magnetic field and resulting in the transonic ion velocity
profile. The global transonic ion velocity profile is also obtained for warm
ions with isotropic and anisotropic distributions. Partial ion reflections are
observed due to a combined effect of the magnetic mirror and time-dependent
fluctuations of the potential as a result of the wave breaking and
instabilities in the regions when the fluid solutions become multi-valued.
Despite partial reflections, the flow of the passing ions still follows the
global accelerating profile defined by the magnetic field profile. In
simulations with reflecting boundary conditions imitating the plasma source and
allowing the transitions between trapped and passing ions, the global nature of
the transonic accelerating solution is revealed as a constraint on the plasma
exhaust velocity that ultimately defines plasma density in the source region.
