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Abstract

The properties of ion bunches stored in an electrostatic ion beam trap (EIBT) have been investigated using the Cryogenic Trap for Fast ion beams (CTF). The extremely high vacuum used rendered the main ion loss mechanism, namely collisions with the rest gas, negligible. Aluminum dimer anions were photo-detached by a pulsed laser to measure the longitudinal ion distribution in the bunch, which for the first time revealed the presence of a dc ion beam component co-existing with the oscillating ion bunch after several hundreds of revolutions. Bunches stabilized by the so-called self-bunching mode of operation have been observed for times as long as 12 s (a factor of 100 longer than previous room-temperature experiments) using N+2 and Al−2 bunches at 6–7.1 keV beam energies after which the bunch abruptly decayed. The decay of the bunch was observed to be intensity dependent and is well reproduced by a model that includes the expansion of the bunch along the beam axis, intrabeam scattering and collisional losses between the bunch and the dc component. Radio-frequency bunching of the ions resulted in the extension of the bunch observation time to 600 s, placing upper limits on all other EIBT ion bunch and trap losses as well as supporting the newly developed decay model and EIBT-adapted bunch dynamics.