  We report on 3D-3V particle-in-cell simulations of fast-ion energy-loss rates
in cold, weakly-magnetized, weakly-coupled plasma where the electron
gyroradius, $\rho_{e}$, is comparable to or less than the Debye length,
$\lambda_{De}$, and the fast-ion velocity exceeds the electron thermal
velocity, a regime in which the electron response may be impeded. These
simulations use explicit algorithms, spatially resolve $\rho_{e}$ and
$\lambda_{De}$, and temporally resolve the electron cyclotron and plasma
frequencies. For mono-energetic dilute fast ions with isotropic velocity
distributions, these scaling studies of the slowing-down time, $\tau_{s}$,
\versus fast-ion charge are in agreement with unmagnetized slowing-down theory;
with an applied magnetic field, no consistent anisotropy between $\tau_{s}$ in
the cross-field and field-parallel directions could be resolved. Scaling the
fast-ion charge is confirmed as a viable way to reduce the required
computational time for each simulation. The implications of these slowing down
processes are described for one magnetic-confinement fusion concept, the small,
advanced-fuel, field-reversed configuration device.
