The ion trap we have developed allows for the storage of fast ion beams (with kinetic energies between hundreds of eV's to few keV's) and uses only electrostatic fields. The ions are injected through a stack of electrodes which are used as an electrostatic mirror, and are confined in a region of few centimeters to a meter, by a similar electrostatic mirror, located on the opposite side. An image of the first ion trap of this kind, which was developed in our laboratory, is shown here. The stability criterion of such a trap can be demonstrated to be similar to the one existing for optical resonator. Basically the only requirement is that the focal length of the mirrors, for a symmetric system, has to be larger than the distance between the mirrors divided by four. Of course, the potential of the last electrodes has to be higher than the kinetic energy of the ions divided by their charge.
There are several advantages in the use of electrostatic fields for trapping charged particles. For example, there are no mass dependence for the electrostatic field, and thus particles of any mass can be stored without retuning the trap, as long as their energy/charge is constant.
We have uses these ion traps for various studies related to the cooling of atomic and molecular ions, as well as for the study of the dynamics of stored ions, which is quite surprising.