Abstract
Detailed experiments and computer simulations employing two beam computational tools commonly used for benchmarking ion beam optics, AXCEL-INP and SIMION, are carried out to investigate the dependence of focal dimensions FD (length and image size) of ion beams extracted from a compact electromagnetic wave driven plasma source. The effect of plasma parameters, such as space potential VP, Bohm velocity vB, and the associated initial kinetic energy Ei, electron Te and ion temperatures Ti, ion mass M, ion current density Ji, and beam related parameters such as beam energy EB, plasma and beam limiter (BL) electrode aperture sizes, and potential applied to lenses (EL1 and EL2), on the FD are investigated. Variation of the focal length fl with vB, VP, and Ei indicates that fl increases with the increase in these parameters; however, it decreases with EB. fl is found to decrease with M and is independent of the BL aperture size; however, it is found to increase with extraction voltage V1 (EL1). Two different theoretical models to estimate the focal length of the combined lens system are developed, and the estimated values of fl are found to agree reasonably well with the experimental and simulation results. The sharpness of focus characterized by the beam angle at the focal point is determined for Ar, Kr, and Ne ion beams. A remarkable feature of nonlinear demagnification in plasma based beams is observed with significant enhancement when the plasma electrode aperture size is reduced to below the Debye length.
Published Version
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