Electrostatic problem for the in-phase radiofrequency trap. (a) The principle of solving the electrostatic problem. The positive charges are shown in red and the negative charges in blue. r_e and r₀ are the radii of the electrodes and the trap, respectively, and L is the distance between the electrodes and the zero-phase plane. (b) Cross section of equipotential surfaces in a trap with r_e = 3 mm, r₀ = 17 mm, and U₀ = 2700 V. Red circles indicate the electrode positions.