The Electrostatic Ion Beam Trap (EIBT)

An ion trap usually stores an ensemble of ions as a cloud, using time dependent electromagnetic fields. We have developed a new type of ion trap, which is able to store an ion beam . There are several advantages to store an ion beam instead of an ion cloud, among them the fact that the direction of the ions is well defined in space, and the possibility to measure with a higher efficiency the reaction of the store ions with a laser beam or electron beam.

Click on the image to see the trap in action 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 the ion trap shown above 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.

During year 2000, we have also finished the development and start the operation of the second generation of ion beam electrostatic trap. The trap, which is shown on the left, allows for trapping the ions on a bent trajectory. The ions can be either stored on a straight line, or they can be steered using an hemispherical deflector toward an additional mirror located at 30 degrees. Such a configuration allows for the study of dissociation process while the beam is stored, as the charged fragments will be deflected to a larger angle than the main beam. A detector, which is located inside the vacuum chamber at a larger angle can detect these fragments. The competition between ionization and fragmentation in small aluminum anions has been measured.

The third generation of traps is now (2009) being planned, the Cryotrap. This setup consist of a linear EIBT operated at very low temperature of ~10 K. The goal of this apparatus is to investigate vibrationlly and rotationally cold molecules.

As of today we know about several other groups around the world where ion traps based on the same principle are being used: Max Planck Institute for Nuclear physics (Heidelberg, GERMANY), Pierre and Marie Curie University (Paris, FRANCE), Bhabha Atomic Research Centre (Mumbai, INDIA), Stockholm (SWEDEN), Queens University Belfast (IRELAND), National Institute for Materials Science (Tsukuba, JAPAN), Louvain-la-Neuve (BELGIUM), Oak Ridge (USA), University of San-Diego (California, USA).

Here is a list of publications related to the operation of the electrostatic ion beam trap: