Pressure Dependence of Space Charge Distribution in the Cathode Fall Region of Ar Hollow Cathode Discharges

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Abstract
The electric field in the cathode fall region of an Ar hollow cathode discharge has been measured by the use of optogalvanic spectroscopy in a gas pressure range from 1 to 6 Torr and at a discharge current from 12 to 20 mA. The radial variation of the field strength follows the mathematical expression derived from the space charge distribution function of ρ( r) = – Ar + B, where r is the radial distance from the cathode axis. In this equation the parameters A and B have been found by curve fitting to follow the formula B = aA + b, in which a is constant at −2.57 ± 0.1 mm when A and B are expressed in units of C/m4 and C/m3, respectively, while b is directly related to the gas pressure. In addition, the current- and pressure-dependent behavior of the cathode fall voltage and the electric field at the cathode surface have been examined.
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