  The formation of the observed core-halo feature in the solar wind electron
velocity distribution function is a long-time puzzle. In this letter based on
the current knowledge of nanoflares we show that the nanoflare-accelerated
electron beams are likely to trigger a strong electron two-stream instability
that generates kinetic Alfv\'en wave and whistler wave turbulence, as we
demonstrated in a previous paper. We further show that the core-halo feature
produced during the origin of kinetic turbulence is likely to originate in the
inner corona and can be preserved as the solar wind escapes to space along open
field lines. We formulate a set of equations to describe the heating processes
observed in the simulation and show that the core-halo temperature ratio of the
solar wind is insensitive to the initial conditions in the corona and is
related to the core-halo density ratio of the solar wind and to the
quasi-saturation property of the two-stream instability at the time when the
exponential decay ends. This relation can be extended to the more general
core-halo-strahl feature in the solar wind. The temperature ratio between the
core and hot components is nearly independent of the heliospheric distance to
the sun. We show that the core-halo relative drift previously reported is a
relic of the fully saturated two stream instability. Our theoretical results
are consistent with the observations while new tests for this model are
provided.
