One-dimensional direct Vlasov simulations of non-stationary plasma expansion in magnetic nozzle

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The one-dimensional (paraxial approximation) transient expansion into vacuum of a collisionless electron-ion plasma guided by a magnetic nozzle is studied numerically. The simulation box, initially empty, has zero boundary conditions for the gyrocenter distribution functions of electrons and ions fe and fi, except at the entry of the nozzle, where particles with a positive axial velocity follow a Maxwellian. The time evolutions of fe and fi are computed with a parallelized direct Vlasov code, which solves a non-stationary guiding center equation for fully magnetized plasmas and discretizes the distribution functions in phase space. The latter involves the (conserved) magnetic moment, and the axial coordinate and velocity of the particles. The gyrocenter distribution functions of the electrons and the ions, aected by the axial components of the electrostatic electric eld and the gradient of the magnetic eld strength, are coupled through Poisson equation in the code. The evolution of macroscopic quantities, like particle density and electrostatic potential proles, are discussed. Relevant kinetic features, such as the evolution of the ions towards a mono-energetic distribution function and the evolution of the plasma temperature proles, are analyzed. The electron trapping, which the stationary models cannot determined self-consistently, and the transient trapping mechanism are captured by the code. This allows an assessment of the impact of the population of trapped electrons and a detailed analysis of their distribution function in terms of axial position, velocity and magnetic moment. Extensions of the code to two-dimensional congurations with axisymmetric geometry, but still fully magnetized plasmas, are discussed.
Proceeding of: 35th International Electric Propulsion Conference (IEPC)
Plasma expansion, Magnetic nozzle, Plasma simulation, Vlasov simulation
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35th International Electric Propulsion Conference (IEPC), October 8-12, 2017, Atlanta, Georgia, USA, 9 pp.