Transition from moving to stationary double layers in a single-ended Q machine

When the cold end-plate of a single ended Q machine is biased positively, large amplitude (<100%) relaxation oscillations are observed in the plasma potential and plate current. These oscillations are associated with double layers that form near the hot plate and travel toward the endplate at about the ion-acoustic velocity where they dissolve. They then form again at the hot plate, the entire process repeating in an oscillatory manner. The authors have studied the effect of applying a large positive bias (>30 V) to the endplate of our Q machine when variable amounts of a neutral gas (Xe, Kr, Ar, Ne and He) are added to the system in both potassium and cesium plasmas. As the neutral pressure is increased, the frequency of the oscillations decrease up to some critical value of the neutral pressure where the oscillations cease. This decrease in frequency is associated with the slowing-down of the moving double layer up to the critical pressure, Pc. At Pc the authors observe a stationary, strong double layer