Symbiosis between low temperature plasma and high temperature chemistry Alexander Gutsol Chevron Energy Technology Company, 100 Chevron Way, Richmond, CA 94802 Abstract: The influence of high temperature chemistry on plasma is not well recognized. Meanwhile, smart utilization of this interaction can substantially improve industrially important plasma chemical processes. Intensive chemical processes result in the formation of excited molecules and chemical ionization. These phenomena are most obvious for flames with good electrical conductivity and light emitted by excited molecules. Even if there is no chemical process but gas temperature is above the threshold of radical appearance, the reactions of radicals create electronically excited molecules. The appearance of these excited molecules without direct electron energy consumption stabilizes the discharge and reduces the required electron energy for ionization. When temperature becomes even higher and reaches the threshold of thermal ionization, the role of radicals in ionization processes becomes insignificant. Discharges can be classified as warm discharges if the discharge temperature is within the temperature range, in which the role of chemistry and/or heat in the discharge “life support” is comparable to that of the electric field. Keywords: warm discharges; step-wise ionization; plasma chemistry; plasma catalysis, discharge stabilization. 1. Introduction This work was inspired by experiments with an elongated atmospheric pressure glow discharge in the reverse vortex (tornado) flow. It was possible to pass continuously through the whole range of available currents (1 – 530 mA) only using helium discharge (Fig. 1). Figure 1. Current – Voltage – Power characteristics obtained in several runs for the discharge with 8.5 L/min flow of helium. Discharges in all other gases were unstable at currents below a certain threshold (around 100 mA) even when available voltage provided by a power supply was much higher than that necessary to support a discharge above the threshold. The shorter the discharge, the lower is the current achievable. Millimeter scale contracted glow discharges can be stable at currents as low as 1.5-2 mA [1]. What is the reason for this dependence and how it is possible to reduce the current and power of long discharges? Study of this topic led to a discussion of the related phenomena of “warm” discharges and to the role of radicals (means chemistry) in discharge support. This paper is an attempt to clarify all these issues. 2. Contraction of a glow discharge Before discussing issues with the stability of contracted glow discharges (CGDs), it is useful to clarify what causes the contraction. Much of the literature on this subject suggests that a glow discharge is unstable with respect to contraction due to thermal or ionization-overheating instability (IOI), and the development of this instability can be presented by the following chain of causal links [2]: n e (jE)TNE/NT e n e  (1)