  A recently proposed technique correlating electric fields and particle
velocity distributions is applied to single-point time series extracted from
linearly unstable, electrostatic numerical simulations. The form of the
correlation, which measures the transfer of phase-space energy density between
the electric field and plasma distributions and had previously been applied to
damped electrostatic systems, is modified to include the effects of drifting
equilibrium distributions of the type that drive counter-streaming and
bump-on-tail instabilities. By using single-point time series, the correlation
is ideal for diagnosing dynamics in systems where access to integrated
quantities, such as energy, is observationally infeasible. The velocity-space
structure of the field-particle correlation is shown to characterize the
underlying physical mechanisms driving unstable systems. The use of this
correlation in simple systems will assist in its eventual application to
turbulent, magnetized plasmas, with the ultimate goal of characterizing the
nature of mechanisms that damp turbulent fluctuations in the solar wind.
