Diagnosis of hydrogen anions (H-,H3-) from the near-electrode region of dielectric-barrier-discharge plasmas

Hydrogen anions (H-,H3-) from the near-ground-electrode region in dielectric barrier discharge hydrogen plasmas were characterized using a molecular-beam mass spectrometer under the pressure of 1.5-60 Torr. The measured H- current is more than one to a few orders of magnitude greater than that of H3- at pressure of 1.5-7.6 Torr with a peak-to-peak voltage of 40 kV and a 35 kHz ac power source. At the gas pressure range of 7.6-60 Torr, only the H- ionic signal is observed. The hydrogen-ion currents rise with the increasing of discharge voltage and ac frequency, but exhibit a maximum over the H2 pressure range studied. The dominant formation mechanism for the H- and H3- anions in the alternative and temporary cathode sheath near the discharge electrode has been discussed. The dependence of the mean energy of H- and H3- anions on H2 pressure has been also obtained