  Stochastic heating is a non-linear heating mechanism driven by the violation
of magnetic moment invariance due to large-amplitude turbulent fluctuations
producing diffusion of ions towards higher kinetic energies in the direction
perpendicular to the magnetic field. It is frequently invoked as a mechanism
responsible for the heating of ions in the solar wind. Here, we quantify for
the first time the proton stochastic heating rate $Q_\perp$ at radial distances
from the Sun as close as $0.16$ au, using measurements from the first two
Parker Solar Probe encounters. Our results for both the amplitude and radial
trend of the heating rate, $Q_\perp \propto r^{-2.5}$, agree with previous
results based on the Helios data set at heliocentric distances from 0.3 to 0.9
au. Also in agreement with previous results, $Q_\perp$ is significantly larger
in the fast solar wind than in the slow solar wind. We identify the tendency in
fast solar wind for cuts of the core proton velocity distribution transverse to
the magnetic field to exhibit a flat-top shape. The observed distribution
agrees with previous theoretical predictions for fast solar wind where
stochastic heating is the dominant heating mechanism.

Solar and Stellar Astrophysics;Plasma Physics