Decay rate measurements in a negative ion rich plasma

By artificially terminating the hydrogen arc discharge in the sheet plasma experiments, the decay rates of the negative and the positive saturation currents of a Langmuir probe could be measured. This technique made it possible to observe, under a deep potential well geometry, two single decay curves of saturation currents, which decayed at the same rate reciprocally with time in the negative ion dominant cold region. This result illustrates that the negative saturation current, which consisted of chiefly electrons, was still proportional to negative ion density. (C) 1998 American Institute of Physics. [S0034-6748(98)01010-7].