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An exhaustive experimental investigation of the conditions required to sustain a plasma column through the propagation of the m=1 mode surface wave has been conducted. It reveals that, given a discharge tube radius a, there corresponds a minimum frequency value fm below which the discharge cannot be achieved; conversely, for a given operating frequency f, the tube radius must exceed some minimum value am for the plasma to be sustained. These minimum conditions required to obtain the discharge are observed to obey a scaling law of the form (fa)m≂const., where the constant is independent of the gas nature and pressure. Theoretically, the dispersion equation of the m=1 mode wave shows no low-frequency cutoff. However, it is found that the specific dependence of the wave attenuation coefficient on the frequency and on the tube diameter can ultimately account for the observed limitations when the wave is used to sustain a plasma. A discharge stability criterion is proposed that recovers the observed scaling law determining the minimum tube radius and wave frequency values.

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The microstructure, electrical properties, aging, and electrolytic decomposition of sputtered CuBr films are described and discussed with respect to the defect chemistry of this mixed Cu+ ion−electron hole conductor. Ammonia gas adsorption increases the electrical resistance of the films. This effect can be used to design a new selective, sensitive, fast, and reversible ammonia gas sensor.

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