A measurement of the effective thickness of the plasma sheath at a cold electrode

The concept of potential sheaths, existing close to cold probes, is commonly used in examining current flow from a plasma to external electrodes. A technique is described by which the effective thickness of this sheath can be determined experimentally, by measuring the capacitance of the electrode-plasma system. It was found that over the temperature range 3500-5000°K the effective sheath thickness is comparable to the Debye length of the plasma. The experimental results presented were obtained in weakly ionized argon at atmospheric pressure.