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

A very low-energy ion beam of an energy level less than 100 eV needs exact evaluation for the energy value. Its energy value is inaccurate unless the plasma potential is taken into account with its total energy. The plasma potential causes the excess energy of a very low-energy ion beam. In this paper, we study the influence of negative ions on the excess energy. In a simple plasma model where the plasma consists 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 negative ions which also change the plasma potential. Theoretical study shows that the existence of negative ions decreases the plasma potential and accordingly lowers the excess energy.