The structure of magnetohydrodynamic (MHD) modes has always been an interesting study in tokamaks. The mode number of tokamak plasma is the most important parameter, which plays a vital role in MHD instabilities. If it could be predicted, then the time of exerting external fields, such as feedback fields and Resonance Helical Field, could be obtained. Autoregressive Integrated Moving Average (ARIMA) and Seasonal Autoregressive Integrated Moving Average are useful models to predict stochastic processes. In this paper, we suggest using ARIMA model to forecast mode number. The ARIMA model shows correct mode number (m = 4) about 0.5 ms in IR-T1 tokamak and equations of Mirnov coil fluctuations are obtained. It is found that the recursive estimates of the ARIMA model parameters change as the plasma mode changes. A discriminator function has been proposed to determine plasma mode based on the recursive estimates of model parameters.

The paper is devoted to the theory of electromagnetic surface waves propagating along the azimuthal direction in cylindrical metal waveguides, which are filled with current-carrying plasmas. The problem is solved by the method of successive approximation. Adequacy of this method application is proved here. To study the coupling of ordinary (O-) and extraordinary (X-) azimuthal modes, the linear theory of the eigenazimuthal X- and O-modes is applied as zero approximation. Plasma particles are described in the framework of magneto-hydrodynamics, electromagnetic fields of the coupled azimuthal modes are determined from Maxwell equations. Spatial distribution of electromagnetic field of these coupled modes and their damping caused for different reasons are studied. Possibility to observe experimentally the phenomena, which accompany propagation of these coupled modes, is estimated numerically. Branches of their possible utilization are discussed as well.

The nonlinear propagation characteristics of Gardner solitons (GSs) in a non-planar (cylindrical and spherical) two-ion-temperature unmagnetized dusty plasma, whose constituents are inertial negative dust, Boltzmann electrons and ions with two distinctive temperatures, are investigated by deriving the modified Gardner (mG) equation. The standard reductive perturbation method is employed to derive the mG equation. The basic features of non-planar dust-acoustic (DA) GSs are analyzed. It has been found that the basic characteristics of GSs, which are shown to exist for the values of ni10/Zdnd0 around 0.311, for ni20/Zdnd0 = 0.5, Ti1/Te = 0.07, and Ti1/Ti2 = 0.05 [where ni10 (ni20) is the lower (higher) temperature ion number density at equilibrium, Ti1 (Ti2) is the lower (higher) temperature of ions, Te is the electron temperature, Zd is the number of electrons residing on the dust grain surface, and nd0 is the equilibrium dust number density] are different from those of Korteweg-de Vries solitons, which do not exist around ni10/Zdnd0 ≃ 0.311. It has been found that the propagation characteristics of non-planar DA GSs significantly differ from those of planar ones.

Arbitrary amplitude and small amplitude ion-acoustic solitary waves (IASWs) have been investigated in a relativistic, collisionless, unmagnetized, and degenerate dense electron–positron–ion plasma. The arbitrary amplitude IASWs have been studied by using the Sagdeev-type pseudo-potential approach. Along with approximate solution, the exact amplitude solitary structure has also been studied numerically. The electrons and positrons are assumed to follow the corresponding Fermi distribution function and the ions are described by the hydrodynamic equations. A new dispersion relation for the ion-acoustic wave has been derived for the relativistic Thomas–Fermi plasma. An energy balance-like equation involving the Sagdeev-type pseudo-potential has been investigated and it has been shown that the concentration of plasma particles has significant effect on the permitted Mach number range of IASWs. Also, it has been pointed out that the only compressional supersonic IASWs can propagate in the relativistic Thomas–Fermi plasma. The present work would be helpful to understand the excitation of the nonlinear ion-acoustic waves in a degenerate plasma, such as in superdense white dwarfs and in the cores of massive planets.

The linear propagation of the low-frequency (compared to the electron gyrofrequency) electromagnetic (EM) waves in a self-gravitating, strongly coupled magnetized plasma with ultra-relativistic degenerate electron fluid is investigated. It is found that the dispersion properties of the EM waves and stability criteria for such a degenerate plasma are significantly modified by the effects of the ultra-relativistic degenerate electron pressure, strong co-relation among extremely dense ion fluid, and the direction of the EM wave propagation relative to the ambient magnetic field direction. The relevance of our investigation to stability of white dwarf stars is briefly discussed. It is particularly seen here that the cores of such stars are stable for the class of gravito-electrodynamic waves that are analyzed for the characteristic ranges of relevant physical parameters.

Dust ion-acoustic solitary structures have been investigated in an unmagnetized non-thermal plasma consisting of negatively charged dust grains, adiabatic positive ions, and non-thermal electrons. Whenever the non-thermal parameter exceeds a critical value, the present system supports negative potential double layer solution. However, this double layer solution is unable to restrict the occurrence of negative potential solitary waves of the present system. As a result, the occurrence of one type of negative potential solitary wave is restricted by Mc < M < MD, whereas the second type of solitary wave exists for all M > MD, where Mc is the lower bound of the Mach number M and MD (> Mc) is the Mach number corresponding to a negative potential double layer. A finite jump between the amplitudes of negative potential solitary waves at M = MD − ϵ1 and M = MD + ϵ2 has been observed, where 0 < ϵ1 < MD − Mc and ϵ2 > 0. Depending on the analytical theory presented in this paper, a numerical scheme has been provided to find the value of the Mach number at which double layer solution exists, and also the amplitude of that double layer. Although the occurrence of coexistence of solitary structures of both polarities is restricted by Mc < M ≤ Mmax, only negative potential solitary wave still exists for all M > Mmax, where Mmax is the upper bound of M for the existence of positive potential solitary waves only. Qualitatively different compositional parameter spaces showing the nature of existing solitary structures of the energy integral have been found. These solution spaces are capable of producing new results and physical ideas for the formation of solitary structures whenever one can move the solution spaces through the family of curves parallel to the curve M = Mc.

Many experimental data along with their theoretical interpretations on the rf low-temperature cylindrical plasma have been issued until today. Our Laboratory has contributed to that research by publishing results and interpretative mathematical models. With the present paper, two issues are being examined; firstly, the estimation of electron drift caused by the rf field gradient, which is the initial reason for the plasma behaviour, and secondly, many new experimental results, especially the electron-neutral collision frequency effect on the other plasma parameters and quantities. Up till now, only the plasma steady state was taken into consideration when a theoretical elaboration was carried out, regardless of the cause and the effect. This indicates the plasma's complicated and chaotic configuration and the need to simplify the problem. In the present work, a classification about the causality of the phenomena is attempted; the rf field gradient electron drift is proved to be the initial cause.

The arbitrary amplitude Langmuir solitons are investigated in an unmagnetized, warm, relativistic plasma, consisting of electrons and positrons. Both the species are considered to have equal non-relativistic temperatures, but can have arbitrary relativistic drift speeds, and their dynamics are governed by fluid equations. Using the Sagdeev psuedo-potential approach, the effects of drift speed, Mach number, and thermal temperature on the amplitude and width of the Langmuir solitons are investigated. For the parameters considered, only rarefactive solitons are found. These solitons represent dip in electron density or electron holes in the configuration space. Existence domain of the Langmuir solitons is limited by the minimum and maximum Mach numbers for given parameters. An increase in the electron (positron) temperature leads to an increase in the Langmuir soliton amplitude and their half-widths. On the other hand, increasing the electron (positron) drift speeds results in decreasing soliton amplitudes and their half-widths. For some typical parameters corresponding to the pulsar magnetosphere, namely electron density ~106 cm−3 and electron thermal velocity of one-tenth of the velocity of light, the electric field of the Langmuir solitons can be of the order of (3–24)kV/m. The presence of such large amplitude electrostatic solitary structures may accelerate electrons and positrons and also produce fine structures of (1–5) microseconds in pulsar radio emissions.

We investigate the Weibel instability in counter-propagating electron–ion plasmas with focus on the ion contribution, considering a realistic mass ratio. A generalized dispersion relation is derived from the relativistic theory by assuming an initially anisotropic temperature, which is represented by a waterbag distribution in momentum space, which shows an enhanced growth rate due to ion response. Two-dimensional particle-in-cell simulations support the theoretical analysis, showing a further amplification of magnetic field on ion time scale. The effect of an initial anisotropic temperature is investigated showing that the growth rate is monotonously decreased if the transverse spread is increased. Nevertheless, the presence of ions generates that the instability can develop for significantly higher electron temperatures. Suppression of oblique mode is also explored by introducing a parallel velocity spread.

A plasma chamber was constructed for the synthesis of ZnS nanoparticles in ionic liquid by glow discharge electrolysis method. Current and voltage (I-V) characteristics of the discharge at the metal–ionic liquid interface showed that the curve follows Ohm's law up to a particular voltage only so that the ZnS nanoparticle preparation was performed after the critical voltage. X-ray diffraction and energy dispersive spectral analysis showed that the samples contain ZnS nanoparticles and also found that tungsten from the metal electrode dissolved in the BMIM[BF4] ionic liquid under plasma and formed tungstic oxide by accepting atmospheric oxygen.

The Paschen curve for D.C. electric field-driven sources like conductively coupled plasmas is examined. The considered plasma gases are metals. The minimum breakdown requirement is related to the ionization energy and the collision cross section of the considered plasma. The dominant collisions to consider may depend on the plasma source.

For vortex-like ion distribution dusty plasmas, the modified KP equation is obtained by using the traditional perturbation method. The growth rate of a solitary wave solution for a higher order disturbance propagating in an arbitrary direction is obtained. We find that the solitary wave is stable under higher order disturbance in this system. However, the growth rate is different with different propagating direction.