Explanation for positive voltage-current characteristics in weakly ionized, low-pressure gas discharge plasmas

Summary form only given. Electric discharge plasmas are generally said to have a "negative V-I (voltage-current) characteristic," which is an informal statement that the voltage across the discharge tends to decrease as the current is increased. For this reason discharges cannot normally be stably powered by ordinary voltage sources. However, there are instances in the literature of positive V-I characteristics in the positive column itself which cannot be attributed to the usual suspects: electrode phenomena, species segregation, high ionization fraction, and so on. The author discusses this topic briefly.