A MICROWAVE PLASMA CATHODE ELECTRON-GUN FOR ION-BEAM NEUTRALIZATION

It is well known that there exist two distinct types of. ion beam neut ralization, viz., charge and current neutralization. We have designed and studied a versatile and compact microwave plasma (MP) cathode elec tron gun dedicated to charge as well as current neutralization. Unlike the conventional hot cathode neutralizer, this MP cathode allows oper ation of the electron gun in a reactive gaseous environment when it is eventually associated with an electron cyclotron resonance (ECR) ion gun. Charge neutralization can be easily carried out by extracting fro m the MP cathode through a 1 mm diameter hole, a 35 mA electron beam u nder a 20 V voltage; the MP cathode being fed with a 75 W microwave po wer at 2.45 GHz. Higher beam intensities could be obtained using a mul tiaperture thin plate. Electron beam intensities as high as 300 mA and energies of 2 keV needed for current neutralization, e.g., when an io n beam impinges onto a thick dielectric surface, are obtained via a tw o-stage arrangement including an anodic chamber associated with a set of three monoaperture plates for the electron beam extraction. Transpo rt of 200-2000 eV electron beams is ensured using focusing optics comp osed of three aligned tubes 6 cm in diameter and unsymmetrically polar ized. (C) 1998 American Institute of Physics.