High-flux source of low-energy neutral beams using reflection of ions from metals

Reflection of low‐energy (<100 eV) ions from surfaces can be applied as a method of producing high‐flux beams of low‐energy neutral particles, and is an important effect in several areas of plasma technology, such as in the edge region of fusion devices. We have developed a beam source based on acceleration and reflection of ions from a magnetically confined coaxial rf plasma source. The beam provides a large enough flux (over 4 A ion current, or 5×1016 atoms/cm2 s at 10‐cm range) to allow the energy distribution of the reflected neutrals to be measured despite the inefficiency of detection, by means of an electrostatic cylindrical mirror analyzer coupled with a quadrupole mass spectrometer. Energy distributions have been measured for oxygen, nitrogen, and inert gas ions incident with from 15 to 70 eV reflected from amorphous metal surfaces of several compositions. For ions of lighter atomic mass than the reflecting metal, reflected beams have peaked energy distributions; beams with the peak at 4–32 eV ha...