Equator-S observations of He+ energization by EMIC waves in the dawnside equatorial magnetosphere

We present Equator‐S observations of He+ energization by electromagnetic ion cyclotron (EMIC) waves in the dawn side equatorial magnetosphere at L > 7. The He+ ions are transversely accelerated up to 2 keV, which is almost an order of magnitude higher than found in previous observations. The heating signatures are correlated, on short time scales (in the order of a few minutes or less), with the presence of EMIC wave emissions in the vicinity of the He+ gyrofrequency (Pc1 frequency range). These events were observed during quiet magnetospheric conditions at the inner edge of the plasmasheet. At this boundary 10 to 40 keV protons, which convect on open drift paths, exhibit a pronounced pitch angle anisotropy providing the free energy for the enhancement of the Pc1 emissions.