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Foreword from the Authors

After our long research and development activities in Plasma science we can state that the plasma is a well controlled environmentally-friendly medium utilizing electric power and enabling the very-high temperature processes and low temperature reactions not available in other methods . This book is, therefore, intended to help the readers interested in the non-thermal gas discharge plasmas and their applications. The content is focused on the microwave-generated plasmas, which have specific properties due to relatively high frequency and which can be used in a number of non-conventional applications. Based on our experience, from university teaching and from communications with the industry people, no broad understanding exists of the microwave power and the microwave plasma systems. People know microwave ovens, but mostly for the heating of meals, and without understanding the principles and specifications of the microwave power. Little knowledge exists about different plasma systems and applications related to microwave power, even though there is apparently growing interest in this technology, mainly for new plasma chemical processes. A motivation for writing this book is based on the authors’ long experience with design and applications of several non-conventional systems and applications, which might stimulate readers when furthering their knowledge and when developing new systems.

The content of this book is composed of five basic parts, i.e. chapters. Chapter 1 is devoted to the microwave techniques and power systems from introducing their short history to the descriptions of individual parts and components in the microwave power lines, which are used in laboratory experiments and many industrial devices. Besides the microwave communication and the radar techniques, a lot of original systems have been developed for heating the plasma in fusion test reactors (Tokamaks, Stellarators, and Magnetic Mirrors), as well as in particle accelerators. Moreover, in the last two decades, interest has rapidly grown in microwave plasma systems working at atmospheric and higher pressures, in gases and inside liquids. Interesting new applications and trends are described in Chapter 6.

We have no intention to write a textbook and start with explanations of basic microwave theories based on Maxwell equations. Excellent comprehensive monographies have been written about microwave engineering with all theories, simulation models, and details, including use of microwaves for generation of the plasma discharges, see e.g. [Refs. 1–7]. However, to make it easier for the book readers without experience in the field of microwave engineering, we introduce the microwave systems in a simple way. We illustrate and describe the most important microwave components and show at least the most important expressions, which can help in greater understanding of the principles, functions, and applications of the microwave components. For these purposes we have also created a large number of original illustrations. Therefore, the text is frequently accompanied by schematic pictures, diagrams, and photographs. Such an approach was promoted and recommended long ago by the “Teacher of the nations,” Johannes Amos Comenius (Komensky in Czech) in his widely translated book “Orbis Sensualium Pictus,” issued in 1658. A copy of this book is available for example in the Hungarian library at the web address https://library.hungaricana.hu/hu/view/RMK_I_1091-RM_I_8r_0547/?pg=0&layout=s. Moreover, at the end of Chapter 1 we have included Part 1.5 describing the microwave oven. This is because each oven represents a smartly engineered microwave system, which can help in the understanding of the basic principles and components in the microwave technology introduced and described in Chapter 1.

After an explanation of the functions of microwave components in the typical power lines for the microwave plasma generation, in Chapter 2, we describe the fundamentals of the gas discharge plasma and differences between plasmas generated by different kinds of the power, with particular emphasis to the microwave power. Chapter 3 is devoted to explanations of interactions of plasmas with solid surfaces and gases, mainly at reduced and low pressures. Used explanations are simplified and limited to basic expressions and equations necessary for the understanding of the processes in the plasma and those caused by the plasma, as described in later chapters. Parts of the texts and some illustrations in Chapters 2 and 3 are used in the authors’ courses for university students, short tutorials at companies and, since 1997, in annual courses for the Society of Vacuum Coaters (www.svc.org) in the United States.

Chapter 4 focuses on different microwave plasma systems, including novel and non-conventional ones developed and laboratory tested in different processing applications at reduced pressures. Chapter 5 is devoted to the microwave plasma systems at atmospheric and higher pressures, including plasmas inside liquids and plasma interactions with the combustion flames. Chapter 6 describes some new applications and trends in microwave plasmas, with short opinions and expectations on future perspectives of the microwave plasma and its applications. Chapter 7 contains appendices with description of symbols, abbreviations, units and values used in the individual chapters.

As mentioned, this book has no ambition to become a “handbook” or a “textbook”. We have written an “easy” text to inspire the readers and raise their interest in further studies and designs of novel systems, as well as to help readers in their experimental works with the microwave plasma and the microwave plasma-assisted applications.

References

1 [1] D. M. Pozar: “Microwave engineering”, 2nd Ed., John Wiley & Sons Inc., New York, 1996.

2 [2] J. C. Slater: “Microwave electronics”, D. Van Nostrand Company Inc., New York, 1951.

3 [3] T. Moreno: “Microwave transmission design data”, Artech House Microwave Library, Boston, MA, 1989. ISBN 089006346X, 9780890063460.

4 [4] L.S. Polak and Yu.A. Lebedev, eds.: “Plasma Chemistry”, Cambridge International Science Publishing, Cambridge, UK, 1998. ISBN 1898326223, 9781898326229.

5 [5] M. Moisan and J. Pelletier, eds.: “Microwave Excited Plasmas Vol. 4”, 1st Ed., Elsevier Science, Amsterdam, Netherlands, 1992.

6 [6] Yu.A. Lebedev, ed.: “Microwave discharges: fundamentals and applications”, Yanus-K, Moscow, 2001. ISBN 5-8037-0066–5.

7 [7] O.A. Popov, ed.: “High density plasma sources”, Noyes Publications, Park Ridge, NJ, 1995. ISBN 0-8155-1377–1.