The growth of a space charge sheath in a low density discharge plasma

摘要

The experiments are made in the positive column of a mercury arc. This plasma column is normally quiescent and a good electric conductor. Typical stationary values of the current density and the field are 10 amps/cm2 and 0.1 volts/ cm. When the stationary discharge current is increased sufficiently, the homogeneous electric field concentrates to a space charge sheath which separates the column in two plasmas with different properties. The sheath is unstable and the current decreases suddenly at a rate between 10 and 10 amps/sec. Sheath voltages as high as 10° volts, provided by the inductive current circuit, may be required to avoid current interruption and stop the current decrease. Then the voltage breaks down and the process may repeat itself about periodically.