Figure 1: The waveform at 1MHZ which has no capcitor

Figure 2:The waveform which the RF voltage is 20VPP

Figure 3 : The waveform which add the capacitor

After we recording the data and seeing the waveform shown in the oscilloscope,  we find that when we increase the frequency, the difference of  plasma's voltage and the whole voltage will be decreased. When the RF voltage rises and the frequency unchanged, the difference of the two voltage becomes bigger. In the case we add a capacitor to the circuit, the waveform of the plasma is nearly a sine wave, which is different with waveform with the capacitor. (In the situation without the capacitor, the plasma voltage is a constant when the RF voltage is negative). If we make the resistor in the current source bigger, the difference of the plasma voltage with the whole voltage will become smaller. It also has been found from the figure that if the frequency or the amplitude of the voltage increased big enough, the waveform will have some distortion.