Particle-in-cell simulations of positive ion and electron beams incident on inhomogeneous radio frequency electric field and multicusp magnetic field boundaries*

Charged particles incident on a region of space in which a radio frequency (RF) electric field exists that grows in strength in the direction of incidence and varies periodically in time may experience a ponderomotive force opposite to the direction of incidence.  This may cause the particles to be reflected back toward their origin; examples include the Paul trap [1], the RF mass spectrometer, and the multipole plasma trap (MPT) [2].  Such devices are usually considered to operate in an adiabatic regime, in which the outgoing kinetic energy is unchanged after reflection.  However, it is also possible to impart a net gain in the average kinetic energy of an ensemble of particles in an incident beam, by deliberate choice of the RF electric field parameters (e.g. frequency; RF voltage; electrode geometry).  The adiabatic and non-adiabatic cases of various charged particle beams interacting with RF multipole electric fields are studied here via particle-in-cell (PIC) simulation using the VSim 12 [3] and PlasmaPy [4] software packages.  Particular cases using helium and argon positive ion beams are emphasized, for use in designing complementary experiments with beam energy analysis.  Electron beam cases are also studied, in concert with the inclusion of a multicusp static magnetic field at the MPT boundary.

[1] W. Paul, Rev. Mod. Phys. 62(3), 531–540 (1990)

[2] N. K. Hicks & D. C. Massin, Results Phys. 17 0–3 (2020)

[3] C. Nieter and J. R. Cary, J. Comput. Phys. 196 448 (2004)

[4] PlasmaPy Community et al. (2023). PlasmaPy, version 2023.5.1, Zenodo, https://doi.org/10.5281/zenodo.8015753