FINITE-ELEMENT MODELING OF CHARGED-PARTICLE DYNAMICS IN A 7 ELECTRODEELECTROSTATIC LEVITATOR

In a conventional vertically oriented quadrupole charged droplets of a ppropriate charge-to-mass (q/m) ratio can be stably levitated at the s addle point, where the potential is a minimum and the electric field i s zero. We are interested in trying to manipulate the q/m by bombardin g a target particle with uni-polar space-charge generated inside the q uadrupole by the inclusion of a pair of auxiliary ''boxer'' electrodes . When operated at low frequencies and voltages these electrodes cause the levitated charged particle to undergo complex trajectories. In th is paper the developement of a very simple but highly effective three- dimensional time-slicing procedure is described, which enables traject ories to be predicted. The technique relies on the superposition of so lution sets to the Laplace equation generated by finite element modell ing, and includes the effects of viscous damping forces. Simulations o f particle trajectories are presented for a range of applied frequenci es, and are shown to be in excellent agreement with experiment.