Numerical investigation on plasma expansion and particle energy in a magnetic nozzle*

A magnetic nozzle is applied to plasma propulsion and has been studied worldwide. In the magnetic nozzle, the plasma expands along the magnetic field lines, and the plasma density decreases in the downstream direction. However, the polytropic process in the magnetic nozzle has not been fully understood yet, and its physics has been discussed in many experiments and simulations. In this study, the plasma expanding through the magnetic nozzle is numerically analyzed using two-dimensional fully kinetic simulations, where particle-in-cell and Monte Carlo collision techniques are employed. Ion and electron motions are kinetically simulated with the electromagnetic field, and the plasma expansion process is investigated depending on the particle energy. Preliminary numerical results show that low- and high-energy electrons indicate the isothermal and adiabatic expansions, respectively, implying that the particle energy has an important role in the magnetic nozzle plasma expansion. In the conference, the plasma expansion and the polytropic process in the magnetic nozzle will be discussed with plasma profiles in detail.