1. Introduction

A partially or fully ionized gas containing neutral atoms, electrons, ions and with the addition of dust particles is known as dusty plasma (DPs). This additional component (dust particle) increases the complexity in the behavior of the system, and thus refers to this system as "dusty" or complex plasma [1]. Nowadays the term "complex plasma" is commonly used in literature to differentiate the dusty plasma. Due to embedded dust particles in the plasma, these dust particles create changes in the charge composition. The new physical processes were introduced in the system such as the recombination of plasma on the particle surface and effects associated with the degeneracy, fluctuations of particle charges which also change the energy and transport phenomena. That's the way the DPs became a new type of non-Hamiltonian systems. The presence of dust particles in the complex plasma is vital for the collective processes. These micro size dust particles create very low-frequency wave mode, which represents charge particle oscillations against the quasi-equilibrium background of ions and electrons. Generally, a dynamical time

scale related to the dust component is in the range of 10–100 Hz. Recently the dusty plasma becomes an interesting field for researchers, technologist and scientists [2, 3]. The initial challenge of fusion in nuclear devices is to confine ionized isotopes of hydrogen atom known as plasma, increase the plasma pressure to initiate and sustain the fusion reaction [4].

Dusty plasma is classified on the basis of density, temperature, potential, and thermal energy. For classification of dusty plasma first, we define Coulomb coupling parameters. Coulomb coupling defines as "the ratio of average potential energy to the average thermal energy of neighboring charged particles" and mathematically written as <sup>Γ</sup> <sup>¼</sup> <sup>Q</sup><sup>2</sup> =4πε0awskBT [5].

### 1.1 Weakly coupled dusty plasmas (WCDPs)

Weakly coupled dusty plasmas have higher average thermal energy than average potential energy due to neighboring charged particles. WCDPs have a high temperature, low density and value of Coulomb coupling parameter less than 1 ð Þ Γ <1 . WCDPs have no structural form due to high temperatures. The background of WCDPs is considered as ionized gases. The temperature of dust particles is much higher than those of ions, electrons, and the neutral population in the system. Due to this, difference in temperature values, DPs becomes a particular interest in the research field of science and technology [6].

### 1.2 Strongly coupled complex dusty plasmas (SCCDPs)

In strongly coupled dusty plasma (SCDP), the average potential energy of neighboring charged particles is dominated on the average thermal energy of the same charged particles. This type of dusty plasma has high charged particles density and low temperature. The SCDPs speedily become emerging fields from last three decades. Due to the presence of dust particles in the atmosphere, the dusty plasma becomes a very significant research field of astrophysical plasma and also in nuclear fusion devices [7–9]. At higher density and low temperature, the SCDPs undergo in crystallization phase. In Coulomb coupling systems, the SCDPs change phase from liquid to crystal phase at specific values of the Coulomb coupling parameters. SCDPs known as a warm liquid at Γ = 5, liquefy at Γ = 80, it becomes cold liquid at Γ = 100, very cold (Γ = 120) and then liquid phase has a limitation at Γ = 137. The SCDP has a crystalline form at Γ = 175 value; it has very high density and very low temperature [10, 11]. SCDPs appear in many astrophysical objects such as neutron star crusts, white dwarf interiors, supernova cores, and giant planetary interiors. Charged particles in dusty plasma are also found in many physical systems such as condensed matter systems of liquid metals and molten salts, cryogenic traps, electrons trapped on the free surface of the helium. DPs play a very important progressing role in laboratory experiments. Nowadays, recently the dusty plasma plays a very significant role in the nuclear fusion devices for plasma confinement and to control the fusion reaction [12]. For basic experiments in the laboratory, the DPs shows very interesting phenomena such as melting and formation of crystals, collective modes excitation with reference to dust component. Nanostructure layered, and colloidal suspension of dusty plasma was also investigated in these set of references [13–15].

#### 1.3 Properties of dust particles

Dust is present everywhere in the space and environment. Dust particles are much larger than electrons, ions, and neutral particles. Their sizes of dust particles Wave Spectra in Dusty Plasmas of Nuclear Fusion Devices DOI: http://dx.doi.org/10.5772/intechopen.91371

vary from hundreds of millimeters to 10 nm and the mass of dust particle is approximately 7.53 <sup>10</sup><sup>10</sup> kg. Their dynamic behaviors are easily observed through a CCD camera because of temporal and spatial scale. These dust particles are mostly negatively charged; however, sometimes they have positive charged also, that depends upon the charging phenomena. The large shielding clouds are created for balance the ion thermal current and electron thermal current. Charging phenomena of dust particles are photoionization, electron bombardment, sputtering, etc. The amount of charge at dust particles depends upon shape and size. Most often, they have spherical shape; however, sometimes they are of the form of rod type and or irregular shape [13, 16]. Dust particles are exposed to ion and electron currents from discharge plasma that's why reached quickly in dynamical equilibrium. The electric charge on the dust particle depends upon their radius (size) and shape, and the charge amount is in the order of 10<sup>3</sup> –10<sup>4</sup> electrons. Increasing the charge on the particles increases the electrostatic repulsion between them in a confined system and may lead to crystallization [17]. The dust particles are strongly coupled due to high electric charges and unable to move easily so that they look like a solid and liquid phase in the DPs. The phonon spectra in the DPs are easily calculated due to the thermal motion of dust particles [18]. The motion of dust particles generates the longitudinal and transverse waves in the dusty plasma. Due to the complex behavior of a dust particle in DPs, it becomes an independent field for researchers whose study dusty plasma with strong correlation. The charged dust particles are highly susceptible to the different forces in the plasma such as the electric field, neutral and ion drag and can serve as sensitive diagnostic tools [19].
