  In collision-poor plasmas from space, e.g., solar wind or stellar outflows,
the heat-flux carried by the strahl or beaming electrons is expected to be
regulated by the self-generated instabilities. Recently, simultaneous field and
particle observations have indeed revealed enhanced whistler-like fluctuations
in the presence of counter-beaming populations of electrons, connecting these
fluctuations to the whistler heat-flux instability (WHFI). This instability is
predicted only for limited conditions of electron beam-plasmas, and was not
captured in numerical simulations yet. In this letter we report the first
simulations of WHFI in particle-in-cell (PIC) setups, realistic for the solar
wind conditions, and without temperature gradients or anisotropies to trigger
the instability in the initiation phase. The velocity distributions have a
complex reaction to the enhanced whistler fluctuations conditioning the
instability saturation by a decrease of the relative drifts combined with
induced (effective) temperature anisotropies (heating the core electrons and
pitch-angle and energy scattering the strahl). These results are in good
agreement with a recent quasilinear approach, and support therefore a largely
accepted belief that WHFI saturates at moderate amplitudes. In anti-sunward
direction the strahl becomes skewed with a pitch-angle distribution decreasing
in width as electron energy increases, that seems to be characteristic to
self-generated whistlers and not to small-scale turbulence.
