Axial momentum gains of ions and electrons in magnetic nozzle acceleration

TL;DR

This study uses kinetic simulations to analyze how ions and electrons gain axial momentum in a magnetic nozzle, revealing that electrons gain significant momentum mainly through Lorentz forces, enhancing thrust.

Contribution

It provides detailed kinetic insights into electron and ion momentum gains in magnetic nozzles, highlighting the dominant role of Lorentz force on electrons.

Findings

Electrons gain net axial momentum via Lorentz force.

Ion acceleration is primarily due to electrostatic force.

Electron momentum conversion from radial to axial increases thrust.

Abstract

The fully kinetic simulations of magnetic nozzle acceleration are conducted to investigate the axial momentum gains of ions and electrons with the electrostatic and Lorentz forces. Axial momentum gains per ion and electron are directly calculated from the kinetics of charged particles, indicating that electrons in the magnetic nozzle obtain the net axial momentum by the Lorentz force even though they are decelerated by the electrostatic force. Whereas ions are also accelerated by the electrostatic force, the axial momentum gain of electrons increases significantly with increasing the magnetic field strength and becomes dominant in the magnetic nozzle. In addition, it is clearly shown that the axial momentum gain of electrons is due to the electron momentum conversion from the radial to axial direction, resulting in the significant increase in the thrust and the exhaust velocity.