A particle-in-cell mechanism by which the sunward electron 'deficit' in the near-Sun solar wind drives its own kinetic instability. The ambipolar electric potential depletes sunward field-aligned electrons, and fully kinetic simulations initialized with realistic Parker Solar Probe / Solar Orbiter velocity distribution functions show this depletion is unstable to quasi-parallel, anti-sunward-propagating whistler waves. Wave-particle resonance scatters suprathermal electrons into the empty sunward phase-space region, gradually erasing the deficit while radiating whistlers. The result explains the regularly observed parallel anti-sunward whistler waves coincident with electron deficits and identifies a non-collisional heat-flux regulation process in the inner heliosphere.
A particle-in-cell (PIC) simulation study of electron kinetics in the inner heliosphere. In-situ Parker Solar Probe and Solar Orbiter data reveal that the solar-wind electron velocity distribution fu…