The excess energy of a low-energy ion beam extracted from a sourceplasma containing negative ions

摘要

A very low-energy ion beam of an energy level less than 100 eVneeds exact evaluation for the energy value. Its energy value isinaccurate unless the plasma potential is taken into account with itstotal energy. The plasma potential causes the excess energy of a verylow-energy ion beam. In this paper, we study the influence of negativeions on the excess energy. In a simple plasma model where the plasmaconsists only of electrons and singly-charged ions of a single specie,the plasma potential is proportional to the electron temperature.However, the real plasma for industrial use often contains some negativeions which also change the plasma potential. Theoretical study showsthat the existence of negative ions decreases the plasma potential andaccordingly lowers the excess energy