The Ring Trap with a single trapped particle. With no static (DC) electric field (left image), the force of gravity (about 10 picoNewtons) pulls the particle down, displacing it from the trap center. At this position the AC electric field drives some particle micromotion, making the particle look like a short streak.  When the DC electric fields are adjusted to balance gravity (qE = mg), the particle moves to the center of the trap.  At this position the AC electric field goes to zero, so there is no longer any observable micromotion.

Electrodynamic Ion Traps