  Using a new technique to directly detect current induced on a nearby
electrode, we measure plasma oscillations in ultracold plasmas, which are
influenced by the inhomogeneous and time-varying density and changing
neutrality. Electronic detection avoids heating and evaporation dynamics
associated with previous measurements and allows us to test the importance of
the plasma neutrality. We apply dc and pulsed electric fields to control the
electron loss rate and find that the charge imbalance of the plasma has a
significant effect on the resonant frequency, in excellent agreement with
recent predictions suggesting coupling to an edge mode.
