Sponsor:
G.S-A was supported by the Ministerio de Economía y Competitividad of Spain (Grant
RYC-2014-15357). J.Z. was supported by Airbus DS (Grant CW240050). J.R. and
M.M-S stays at UC3M for this research were supported by a UC3M-Santander Chair of Excellence and by National R&D Plan (Grant ESP2016-75887), respectively. E.A. was
supported by the MINOTOR project, that received funding from the European Unions
Horizon 2020 research and innovation programme, under grant agreement 730028.
Project:
info:eu-repo/grantAgreement/EC/H2020/730028 Gobierno de España. RYC-2014-15357 Gobierno de España. ESP2016-75887
Keywords:
Electric propulsion
,
Magnetic nozzles
,
Electron trapping
The paraxial expansion of a collisionless plasma jet into vacuum, guided by a magnetic nozzle, is studied with an Eulerian and non-stationary Vlasov&-Poisson solver. Parametric analyzes varying the magnetic field expansion rate, the size of the simulation box,The paraxial expansion of a collisionless plasma jet into vacuum, guided by a magnetic nozzle, is studied with an Eulerian and non-stationary Vlasov&-Poisson solver. Parametric analyzes varying the magnetic field expansion rate, the size of the simulation box, and the electrostatic potential fall are presented. After choosing the potential fall leading to a zero net current beam, the steady states of the simulations exhibit a quasi-neutral region followed by a downstream sheath. The latter, an unavoidable consequence of the finite size of the computational domain, does not affect the quasineutral region if the box size is chosen appropriately. The steady state presents a strong decay of the perpendicular temperature of the electrons, whose profile versus the inverse of the magnetic field does not depend on the expansion rate within the quasi-neutral region. As a consequence, the electron distribution function is highly anisotropic downstream. The simulations revealed that the ions reach a higher velocity during the transient than in the steady state and their distribution functions are not far from mono-energetic. The density percentage of the population of electrons trapped during the transient, which is computed self-consistently by the code, is up to 25% of the total electron density in the quasi-neutral region. It is demonstrated that the exact amount depends on the history of the system and the steady state is not unique. Nevertheless, the amount of trapped electrons is smaller than the one assumed heuristically by kinetic stationary theories.[+][-]