Characterization of modified 90̂ cylindrical energy analyzer with electron beam

Abstract

The Heavy Ion Beam Diagnostic (HIBD) installed on the small ISTTOK tokamak is based on Xe+ species primary beam injector (E0 = 25 keV of energy) and a multiple cell array detector (MCAD) of secondary, Xe2+, ions. In this mode of operation, a compact multiple-channel 90̂ cylindrical energy analyzer (CEA) was proposed. In simulations using SIMION code significant improvements of energy resolution and strong decrease of the angular aberration coefficient due to lensing properties of fringing field were obtained with deceleration of ions inside CEA and detection at decelerating potential. Recently, the simulations have been extended to investigate the influences on the measurements of the CEA housing chamber and the secondary electron emission (SEE) from the deceleration/detector plate. To shield the electric field perturbations introduced by the chamber, two guard rings (GR) have been added on top and bottom between CEA plates. To overcome the SEE effect, the detector part has been modified by adding two grids and ions detection at zero potential. The GR dimensions and position, and the distances between the grids and detector plate have been optimized by SIMION code. This paper presents the results of numerical simulations and experiments, obtained with the modified CEA in normal and two-times deceleration modes using electron beam. The energy resolution of (Δ E/E0) ∼ 2.4× 10−3 has been demonstrated in deceleration mode insensitive to the Δ θin = ± 1̂ change of the analyzed beam entrance angle. Good agreement between the experimental results and the numerical simulation predictions has been obtained.