  In this work, a quasi-linear model for plasma flow response to the resonant
magnetic perturbation (RMP) in a tokamak has been rigorously developed in the
resistive-inertial (RI) and viscous-resistive (VR) regimes purely from the
two-field reduced MHD model. Models for plasma response to RMP are commonly
composed of equations for the resonant magnetic field response (i.e. the
magnetic island) and the torque balance of plasma flow. However, in previous
plasma response models, the magnetic island and the torque balance equations
are often derived separately from reduced MHD and full MHD equations,
respectively. By contrast, in this work we derive both the magnetic island
response and the torque balance equations in a quasi-linear model for plasma
flow response entirely from a set of two-field reduced MHD equations. Such a
quasi-linear model can recover previous plasma flow response models within
certain limits and approximations. Furthermore, the physical origins of
quasi-linear forces and moments in the flow response equation are also
accurately calculated and clarified self-consistently.
