The discovery of energetic He⁺ions in the magnetosphere

The presence of He+ ions with energies up to 1.4 keV has been detected on two occasions by energetic ion mass spectrometer experiments on the low-altitude polar satellites 1969-25B and 1971-089A. The peak energy flux of the He+ ions was 0.03 erg/cm² s sr and occurred at L = 7 and a magnetic local time of 07 hours. The He+ ions were accompanied by protons in the same energy range and O+ ions of somewhat higher energies. No He++ ions were observed on either occasion. In one event the He+ and O+ ions are shown to have similar velocity spectrums. It is concluded that the He+ is most likely of ionospheric origin, perhaps accelerated by the same mechanism that accelerates the O+.