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.

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.

Figure 1: The waveform of the plasma voltage and the whole voltage in the circuit

Figure 2: The voltage waveform across the battery and the diode

In the week four and five, we tested the while circuit with different situations. First, we test the circuit of the plasma shown in the reference paper which only have the diode and the current source. The RF voltage is 10vpp and the frequency is 500kHZ. And then, we make the RF voltage unchanged and alter the frequency to find out if the frequency has the influence to the experiment result. Next, we keep the frequency to 500kHZ and change the voltage. Moreover, we parallel the capacitor to the circuit to find out the difference of the waveform between the circuit without the capacitor. Finally, we change the resistance of the current source to change the current to find out if the current source has some effect in the waveform of the plasma voltage.