  A quasilinear plasma transport theory that incorporates Fokker-Planck
dynamical friction (drag) and scattering is self-consistently derived from
first principles for an isolated, marginally-unstable mode resonating with an
energetic minority species. It is found that drag fundamentally changes the
structure of the wave-particle resonance, breaking its symmetry and leading to
the shifting and splitting of resonance lines. In contrast, scattering broadens
the resonance in a symmetric fashion. Comparison with fully nonlinear
simulations shows that the proposed quasilinear system preserves the exact
instability saturation amplitude and the corresponding particle redistribution
of the fully nonlinear theory. Even though drag is shown to lead to a
relatively small resonance shift, it underpins major changes in the
redistribution of resonant particles. These findings suggest that drag can play
a key role in modeling the energetic particle confinement in future burning
fusion plasmas.
