Design of an energy analyzer for low energy 1+ charged ion beams at RISP Project

Accurate measurement of the energy spread with a compact device has been accomplished by developing a new prototype of a retarding field energy analyzer (RFEA). The device is capable of handling all kinds of low energy mono-charged ion beams at RISP Project. Numerical simulations have been performed in order to study and evaluate dependency of RFEA energy resolution to beam emittance, beam energy, beam energy spread, space charge effects, and most significantly the optics system. Simulation results have shown that the use of developed optics system with particular voltage applied on the focusing cylinder and suitable positioning of the retarding grid may lead to high efficiency energy resolutions not exceeding 0.31 eV for beam energy going up to 20 keV. Small errors on the measured energy spread are obtained despite the presence of degradations stemming from various energy resolution dependencies. Typical mono-charged ion beams delivered from ion trap devices, ISOL beam-line and stable ion sources have been studied. The error on the optimum measured energy spread for beams delivered from ion trap devices is 5 similar to 10% owing to beam emittances. For a larger beam size, delivered from an ISOL beam-line, a larger error occurs on the measured energy spread at around 23.5%. The energy spread of ion beams delivered from stable ion sources with good optical quality relative to the ISOL sources can be measured with an error around 21.7%. This prototype enables accurate measurement of the average beam energy with an error around 1.5 eV per 20 keV beam energy.