  The high cadence plasma, electric, and magnetic field measurements by the
Magnetospheric MultiScale spacecraft allow us to explore the near-Earth space
plasma with an unprecedented time and spatial resolution, resolving
electron-scale structures that naturally emerge from plasma complex dynamics.
The formation of small-scale turbulent features is often associated to
structured, non-Maxwellian particle velocity distribution functions that are
not at thermodynamic equilibrium. Using measurements in the terrestrial
magnetosheath, this study focuses on regions presenting bumps in the power
spectral density of the parallel electric field at sub-proton scales.
Correspondingly, it is found that the ion velocity distribution functions
exhibit beam-like features at nearly the local ion thermal speed. Ion cyclotron
waves in the ion-scale range are frequently observed at the same locations.
These observations, supported by numerical simulations, are consistent with the
generation of ion-bulk waves that propagate at the ion thermal speed. This
represents a new branch of efficient energy transfer at small scales, which may
be relevant to weakly collisional astrophysical plasmas.
