Operation of an electrostatic ion trap in a uniform magnetic field

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Abstract
The electrostatic ion trap consisting of an outer cylinder with end caps plus a concentric central wire is relatively easy to construct compared to rf and Penning ion traps. Its use in a uniform magnetic field of several Gauss has been studied so that, for example, optical pumping of the trapped ions would be possible for an appropriate ionic species. Initial investigations using either He or Ar ions trapped in the approximately logarithmic potential between the outer cylinder and the central wire indicate that the trapping time is slightly reduced when a 25–50 G magnetic field is applied parallel to the trap axis. However, the use of the magnetic field allows the trap to be filled initially with substantially more ions. Computer plots of numerous nonperiodic ion orbits for several revolutions both with and without a magnetic field serve as a guide to understanding the operation of the trap in a uniform magnetic field. These plots show that the major features of the trajectories remain unchanged for magnetic fields up to 100 G, although ions with almost zero initial angular momentum about the central wire can be trapped when a magnetic field is present.