New observations from the FAST satellite demonstrate strong wave-particle interactions between energetic electrons and H+ EMIC waves in inverted-V arcs. The intense waves are shown to occur in strong upward current regions which contain intense downgoing field-aligned electron fluxes. Electrons near the inverted-V spectral peak have large, factor of 2 to 10, coherent flux modulations at or near the wave frequency. The electron modulations are typically centered at about fCH+/2, where fCH+ is the local H+ cyclotron frequency. The EMIC waves are broadbanded, extending from about 0.3fCH+ to 0.7fCH+. These waves also accelerate cold secondary electrons, forming counterstreaming field-aligned electrons at energies up to about 300 eV. In addition, electron modulations at fCH+ are observed in the density cavities associated with upgoing ion beams. Intense waves at fCH+ are simultaneously detected and shown to have a magnetic component similar to the EMIC waves. ¿ 1998 American Geophysical Union