Deceleration and ion beam optics in the regime of 10–200 eV

Abstract

A deceleration lens system for low energy ion beam transport applications in the region of 10–200 eV has been designed, constructed and experimentally characterized. In this ion beam system, the target is required to be in an almost field-free region at the exit of the lens to allow for maximum target maneuverability. The lens design was optimized using the simulation data obtained with chden, a computer program for calculating ion trajectories with space-charge included. The design chosen in this work was a five-electrode lens which can be operated in either a simplified two-electrode deceleration mode or, when the best system performance is required, in a five-electrode decelerator-focusing mode. The performance of the lens was experimentally evaluated by using a 3 keV pure argon ion beam with a beam size of about 1 mm2 and beam current of about 10μA which was generated by a modified Colutron Ion Gun Model G-2 unit. The lens decelerated the incident beam to 10–200 eV and transported it to either a Faraday cage for beam current and beam profile measurements or to a quadrupole mass spectrometer equipped with a cylindrical ion energy analyzer for beam energy and mass characterization. The results indicated that the lens could deliver an ion current density of approximately 100 μA/cm2 at ion energies higher than 50 eV. The available current density dropped with decreasing energies but remained at more than 10 μA/cm2 at 10 eV.