Particle-in-cell simulations and experimental design study of energy modification of a charged particle beam incident on a region of inhomogeneous radio frequency electric field

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 [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 11 software package [3]. Along with RF electrodes and charged particle emitters, a retarding field energy analyzer is added to the model to simulate experimental observation of the energy distribution of the outgoing beams. The PIC simulations serve as the basis for an experimental design in which electron and ion beams are directed at an array of RF electrodes (driven at ~10 MHz for ions, and ~100 MHz for electrons), and the reflected (and transmitted) energy distributions are measured. The inclusion of a multicusp static magnetic field is also investigated, for its role in enhancing electron reflection.

[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)