The Ion Energy Distribution in an Electron Beam Ion Trap

We have inferred the energy distribution of trapped ions in an electron beam ion trap (EBIT) based on visible light images of the ion cloud. For this, we the Fe XIV line at 5303 Angstroms. That line arises from a metastable level whose lifetime is orders of magnitude longer than the orbital period. Consequently, the emission occurs throughout the ion cloud. We simulated the ion cloud by computing ion trajectories in EBIT. Because energy is conserved, the ion energy distribution used to initialize the trajectories is a constant. By iteratively comparing the model ion cloud to the observed one, we infer the statistical distribution of ion energies in the trap. We find that the average ion energy is proportional to the electron beam current. A larger electron beam current leads to greater electrostatic trapping so that higher energy ions remain trapped. This work is supported by the NASA H-TIDES program and work at LLNL is performed under the auspices of the US DOE under contract No. DE-AC52-07NA27344.