Energy analysis of hyperthermal hydrogen atoms generated through surface neutralisation of ions

Hydrogen ions (H+, H-2(+) and H-3(+)) are produced in a magnetically confined inductively coupled radio frequency plasma. Ions are accelerated in the plasma boundary sheath potential, of several hundred volts, in front of a biased metal electrode immersed in the plasma. Backscattered hyperthermal hydrogen atoms are investigated by optical emission spectroscopy and an energy-resolved mass spectrometer. Ionisation of fast neutrals through electron stripping of atoms in the plasma allows energy analysis of the resulting ions. Thereby, the energy distribution function of the hyperthermal atoms can be deduced. The energy spectra can be explained as a superposition of individual spectra of the various ion species. The measured spectra also shows contributions of negative ions created at the electrode surface. In addition to experimental measurements, simulations of the neutral flux of backscattered atoms are carried out.