Design of a Hollow-Beam Electron Optics System With Control Focus Electrodes Ma, Tongli ; Zhao, Ding ; Zhang, Zhaochuan ; Xiang, Yidong ; Wang, Weilong Abstract Publication: IEEE Transactions on Plasma Science Pub Date: April 2019 DOI: 10.1109/TPS.2019.2902455 Bibcode: 2019ITPS...47.1762M