**1. Introduction**

In recent years, the most promising method for creating low–temperature plasma is the method of microwave heating. As of now, gas–discharge plasma is effectively used in various fields, including microwave electronics, lighting technology, medicine, plasma chemistry, etc. The use of microwave heating to excite gases and to create plasma allows significantly to reduce the overall dimensions of devices. This is a very current task especially under creating small-size devices, including the annular laser gyroscopes, different types of lasers, electrodeless plasma lamps, etc. [1].

Created designs of a miniature helium-neon laser and a source of incoherent optical radiation based on an electrodeless sulfur lamp are shown in **Figure 1** [2, 3]. The unifying factor of these structures is the method of microwave excitation (heating) of the gas mixture in the working volume of the devices. Considering the

formation of plasma with the necessary quantitative characteristics. To solve such a problem, it is necessary to develop a mathematical model of the plasma, the use of which will make it possible to estimate the quantitative parameters of the gas (gas

On the other hand, the process of ionization of the active medium (gas or gas mixture) occurs as a result of the action of a regular electromagnetic field. One of the conditions for effective plasma heating is the arrangement of an active medium into an area with the maximum intensity of the electric component of the regular electromagnetic field. To achieve this, it is necessary to know the distribution of the components of the electromagnetic field in the volume of the electrodynamic structure, which requires additional studies of its properties. Currently, there are two approaches to the formation of an electromagnetic field with the aim of its subsequent use for exciting or heating various media: resonance (or a regime of a standing wave) and interference, when two traveling waves add up to give a resultant standing wave [3]. In the first case, a regular electromagnetic field is excited in a resonator. The shape and dimensions of the given resonator are selected from the conditions of the frequency range used, taking into account the maximum intrinsic quality factor of the oscillatory system. The interference method of forming a standing wave involves the use of two traveling waves moving towards each other. To implement this approach, a regular waveguide is used, inside which a

Thus, in order to increase the efficiency of conversion of the energy of the electromagnetic field into the internal energy of the gas–discharge medium, it is necessary to a knowledge of the distribution of a regular electromagnetic field as

In the latter case, it is important to further develop the theory of plasma processes taking into account their chaotization, as well as to understand the conditions for the occurrence of regimes with dynamic chaos (conditions of stochastic heating

In the given chapter the theoretical and experimental studies of microwave heating of plasma by an electromagnetic field are discussed. The conditions for increasing the efficiency of the microwave heating at the expense of enhancing the intensity of a regular electromagnetic field or using dynamic chaos mode, including the methods of its achieving (the cases of Cherenkov's and cyclotron resonances) are determined. The computer modeling results of electrodynamic systems are presented and the process of formation of a standing electromagnetic wave in electrodynamic systems (resonator and waveguide) is investigated, conditions for a local increase of intensity of the regular field in the region of the active medium are

As mentioned above, the energy of the microwave electromagnetic field is used to excite and heat the plasma. Various designs of oscillatory structures (resonators) are used as electrodynamic structures that form fields with the required distribution

of power lines, the type and shape of which depend on the frequency of the electromagnetic field used. For example, for the excitation (pumping) of the active medium in helium-neon lasers, electromagnetic oscillations are used, the frequency of which lies in the range of 200 … 400 MHz with an average microwave power level of 2 … 5 W. In this case, a classical oscillatory circuit in the form of a flat capacitor is used as an oscillatory electrodynamic system. **Figure 2** shows the design of such a capacitor, the results of simulation and experiment [4]. An analysis of the

well as an understanding of the physical processes in the active medium.

**2. Computer modeling of the electrodynamic systems**

mixture) to provide the necessary plasma characteristics.

*Microwave Heating of Low-Temperature Plasma and Its Application*

*DOI: http://dx.doi.org/10.5772/intechopen.97167*

bulb with an active medium is placed.

of plasma).

determined.

**125**

#### **Figure 1.**

*Examples of structural elements of sources of electromagnetic radiation with microwave excitation. A ring laser gyroscope [2] (a) and an optical radiation source based on an electrodeless sulfur lamp (b) [2].*

significant difference in the frequencies of the exciting microwave field, the designs of electrodynamic systems, in the volume of which a regular electromagnetic field is formed, have significant differences. These features of the excitation elements must be taken into account when designing devices, the operation of which is based on the use of gas-discharge media (plasma).

The analysis shows that the main structural elements of these devices are the active medium and the electrodynamic system for the formation of a regular electromagnetic field. A gas or a gas mixture (sometimes with the addition of an impurity, for example, sulfur S8, as in the case of a sulfur lamp) is considered as an active medium with nonlinear properties. Under the action of an external microwave electromagnetic field, the gas mixture is ionized and plasma is formed. At this stage, it is important to understand the ongoing physical processes that underlie the

#### *Microwave Heating of Low-Temperature Plasma and Its Application DOI: http://dx.doi.org/10.5772/intechopen.97167*

formation of plasma with the necessary quantitative characteristics. To solve such a problem, it is necessary to develop a mathematical model of the plasma, the use of which will make it possible to estimate the quantitative parameters of the gas (gas mixture) to provide the necessary plasma characteristics.

On the other hand, the process of ionization of the active medium (gas or gas mixture) occurs as a result of the action of a regular electromagnetic field. One of the conditions for effective plasma heating is the arrangement of an active medium into an area with the maximum intensity of the electric component of the regular electromagnetic field. To achieve this, it is necessary to know the distribution of the components of the electromagnetic field in the volume of the electrodynamic structure, which requires additional studies of its properties. Currently, there are two approaches to the formation of an electromagnetic field with the aim of its subsequent use for exciting or heating various media: resonance (or a regime of a standing wave) and interference, when two traveling waves add up to give a resultant standing wave [3]. In the first case, a regular electromagnetic field is excited in a resonator. The shape and dimensions of the given resonator are selected from the conditions of the frequency range used, taking into account the maximum intrinsic quality factor of the oscillatory system. The interference method of forming a standing wave involves the use of two traveling waves moving towards each other. To implement this approach, a regular waveguide is used, inside which a bulb with an active medium is placed.

Thus, in order to increase the efficiency of conversion of the energy of the electromagnetic field into the internal energy of the gas–discharge medium, it is necessary to a knowledge of the distribution of a regular electromagnetic field as well as an understanding of the physical processes in the active medium.

In the latter case, it is important to further develop the theory of plasma processes taking into account their chaotization, as well as to understand the conditions for the occurrence of regimes with dynamic chaos (conditions of stochastic heating of plasma).

In the given chapter the theoretical and experimental studies of microwave heating of plasma by an electromagnetic field are discussed. The conditions for increasing the efficiency of the microwave heating at the expense of enhancing the intensity of a regular electromagnetic field or using dynamic chaos mode, including the methods of its achieving (the cases of Cherenkov's and cyclotron resonances) are determined. The computer modeling results of electrodynamic systems are presented and the process of formation of a standing electromagnetic wave in electrodynamic systems (resonator and waveguide) is investigated, conditions for a local increase of intensity of the regular field in the region of the active medium are determined.
