In the theory, the difference between the plasma voltage and the whole voltage is the voltage across the diode. When the RF voltage is negative,the plasma voltage is the voltage across the diode from the other side. Therefore, it is a negative constant. The batteries shown in the previous circuit did not used in the circuit in practice, it does not affect the result of the waveform. When there is no displacement current in the circuit, at most time the ion current flows into the diode. When take the displacement into account the electron current will flow to the electrode when the voltage in the sheath is small.