Reducing the Transition Hysteresis of Inductive Plasmas by a Microwave Ignition Aid

Inductive plasma discharge has been a part of continuous investigations since it was discovered. Especially the E- to H-mode transition and the hysteresis behavior have been topics of research in the last few decades. In this paper, we demonstrate a way to reduce the hysteresis behavior by the usage of a microwave ignition system. With this system, a significant decrease of the needed coil current for the ignition of the inductive driven plasma is realized. For the microwave generation, a magnetron as in a conventional microwave oven is used, which offers a relatively inexpensive way for microwave ignition aid. At the measured pressure of 7.5 Pa, it was possible to reduce the needed coil current for the inductive mode transition by a factor of 3.75 compared to the mode transition current without the ignition aid. This was achieved by initiating the transition by a few seconds of microwave coupling. The performed simulations suggested that the factor can be further increased at higher pressures. That is especially interesting for plasmas that are hard to ignite or for RF-sources that cannot deliver high enough currents or frequencies for the ignition.

Microwave Ignition for the Pulse Detonation Engine

The Pulse Detonation Engine (PDE) is now offering the Aviation Industry a new, efficient and cheap mode of propulsion. Outside of the valving of the fuel and the air, the basic design of the PDE contains no moving parts: it is merely a tube in which some fuel is detonated, and the resultant shock wave used for propulsion. It suffers, however, from the lack of an appropriate ignition system designed especially for this propulsion technique. This paper discusses the possibility of using microwave radiation to initiate detonation in the PDE. Background information regarding the PDE, the merits of detonation over deflagration, and extant techniques for initiating detonation is included. The merits of this technique over the more traditional methods are emphasized. A practical technique of producing and controlling microwave radiation is subsequently presented. To prove viability of the central idea, a list of public patents related to the previous work done regarding the use of microwave radiation to initiate ignition is presented, along with a short summary related to each entry. This area of research is still new and unorthodox, as far as both the PDE and microwave ignition are concerned, and no work has been done until now that involves both of these. Further experiments involving realistic fuels and conditions to demonstrate the viability and practical use of this technique are required. It is expected that this research will do for the PDE what invention of spark plugs did for the gasoline (or Spark Ignition) engine.