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The schematic of the experimental setup showing the technique to determine the resonance peak using the reflection-mode technique. The instrumentation involves a wide bandwidth (1.0–) directional coupler (Model: Pasternack, PE 2214-10), a diode detector (Model: Pasternack PE8013) having bandwidth (0.01–), with the Tektronix TDS 3034B oscilloscope arrangement to detect the resonance peak.
The wave form showing the reflection modulus of the transmission line with and without the plasma. The resonance peak in the plasma is identified by taking the online difference between these two signals. The dip in the difference signal for two different powers of exactly coincides with the vacuum resonance peak, whereas resonance peak, , moves to higher frequency upon increasing the at a constant . The corresponding densities are indicated in Fig. 3.
Electron density with increase in discharge power for two sets of constant power. The plasma densities were measured at off center in the midplane between the two electrodes.
(a) The discharge voltage and total discharge current , plotted as a function of rf power. The rf powers, currents, and voltages are measured on the output of the matchbox immediately adjacent to the electrode. The electrode area is . Note that the voltage (and current) changes, whereas is constant at 200 and . (b) Phase shifts between voltages and currents for 2 and rf.
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