Dust-acoustic and dust-lower-hybrid diamagnetic drift wave instabilities have been examined in a collisional non-uniform quantum dusty magnetoplasma. The dust-acoustic drift instability arises through the Fermi degenerate pressure of electrons for a high-density plasma, while for a relatively low-density collisional quantum plasma and short wavelength consideration, the instability is dominated by the Bohm potential effect exciting a new quantum dust-acoustic wave. In the long-range wavelength limit, dust-lower-hybrid waves are found to be unstable because of the diamagnetic drift of magnetized ions. Various possible instability conditions are found for diamagnetic drift instability.

A well-optimized design of an ion cyclotron resonance heating (ICRH) antenna is very important for steady-state plasma heating with high radio frequency (RF) power of several tens of megawatts. However, a sharp decrease in the coupling RF power because of impedance mismatch of ICRH system is an issue that must be resolved for present-day fusion reactors and International Thermonuclear Experimental Reactor. This paper has theoretically analyzed the ICRH antenna's impedance matching for ELMy plasmas on experimental advanced superconducting tokamak (EAST) by the transmission line theory. The results indicate that judicious choice of the optimal feeder location is found useful for adjustable capacitors' tolerance to the variations of the antenna input impedance during edge-localized mode (ELM) discharge, which is expected to be good for the design of ICRH antenna system and for real-time feedback control during ELM discharge on EAST.

Non-planar (cylindrical and spherical) double layers (DLs) in two-ion-temperature dusty plasma, whose constituents are inertial negative dust, ions with two distinctive temperatures, and Boltzmann electrons, are studied by employing the reductive perturbation method. The modified Gardner equation describing the nonlinear propagation of dust-acoustic (DA) waves is derived, and its non-planar double layer solutions are analyzed numerically. The parametric regimes for the existence of DA DLs, which are found to be associated with positive potential only, are obtained. The basic features of non-planar DA DLs, which are found to be different from planar ones, are also identified. The implications of our results to different space and laboratory dusty plasma situations are discussed.

Understanding the origin and nature of turbulent transport in tokomak plasmas is one of the major challenges of a successful magnetic confinement fusion. The aim of this work is to study instability associated with the ion-temperature gradient (ITG)-driven turbulence in the core of the plasma, which is the seat of fusion reactions. We used a low degree of freedom model composed of 18 ordinary differential equations. When the system is slightly above the stability threshold of the ITG mode, it is considered to be in the convection regime and convective heat transport of the system is time-independent, or oscillates periodically. As ITG is increased further, the system bifurcates to the turbulent regime. In a strongly turbulent regime, intermittent bursts (the so-called avalanches) are observed. This intermittency is a result of the competition among the following three factors: generation of sheared flows and suppression of ITG turbulence, gradual reduction of the sheared flows due to viscosity, and rapid regrowth of ITG modes due to reduction of sheared flows.

An atmospheric pressure plasma jet is generated with a cold arc discharge in ambient air. The current-voltage characteristics and optical emission spectra of plasma discharges are investigated. The molecular nitrogen (N2), hydroxyl radical (OH), and oxygen atom (O) are observed and analyzed. Based on the best fit of the simulated spectra of N2 (C3∏u+ − B3∏g+) band and OH (A2∑+ − X2∏) band transition and the experimentally recorded spectra, the rotational temperature and the vibrational temperature of atmospheric pressure cold arc plasma jet (APCAPJ) are estimated.

Linear electrostatic waves in a magnetized four-component, two-temperature electron–positron plasma are investigated, with the hot species having the Boltzmann density distribution and the dynamics of cooler species governed by fluid equations with finite temperatures. A linear dispersion relation for electrostatic waves is derived for the model and analyzed for different wave modes. Analysis of the dispersion relation for perpendicular wave propagation yields a cyclotron mode with contributions from both cooler and hot species, which in the absence of hot species goes over to the upper hybrid mode of cooler species. For parallel propagation, both electron-acoustic and electron plasma modes are obtained, whereas for a single-temperature electron–positron plasma, only electron plasma mode can exist. Dispersion characteristics of these modes at different propagation angles are studied numerically.

A theoretical investigation of the basic characteristics of cylindrical and spherical dust-ion-acoustic (DIA) solitary waves (SWs) is made in a dusty non-thermal plasma, whose constituents are non-thermal electrons, inertial ions, and arbitrarily charged stationary dust. The reductive perturbation method is used to derive the modified Gardner equation. The latter is numerically analyzed for both positively and negatively charged dust. The basic features of cylindrical and spherical DIA SWs, which are found to exist in such a dusty non-thermal plasma, are identified. The implications of our results to both space and laboratory plasma situations are also discussed briefly.

A pre-bunched relativistic electron beam (REB) counter-propagating to the surface wave in the vacuum region Compton backscatters the surface wave into a high-frequency coherent radiation. Plasma supports the surface wave that acquires a large wave number k0z around pump wave frequency $\omega _0 = {{\omega _p } {/ {\vphantom {{\omega _p } {\sqrt 2 }}} \kern-\nulldelimiterspace} {\sqrt 2 }}$, where ωp is the plasma frequency. The surface wave extends into the vacuum region and can be employed as a wiggler for the generation of sub-millimeter waves. The growth rate, efficiency, and gain were evaluated based on experimentally known parameters relevant to free electron laser (FEL). It was found that the growth rate, efficiency, and gain of the surface wave-pumped FEL increase with the modulation index Δ, which has the maximum value when approaching unity in addition to when the frequency and wave number of the pre-bunched beam are comparable to that of the radiation wave, i.e., ω01 ~ ω1 and k01 ~ k1. The growth rate of FEL instability scales as one-third power of beam density in the Compton regime.

In this paper, a homogeneous system of unmagnetized collisionless plasma consisting of a cold electron fluid, low-temperature ion obeying Boltzmann-type distribution and high-temperature ion obeying non-thermal distribution is considered. The perturbation method with two different forms of stretching will be considered to drive the KdV and modified KdV (mKdV) equations. The Agrawal's method is applied to formulate the time-fractional KdV and mKdV equations. A variational iteration method is used to solve these equations. The results show that the fractional order of the differential equations can be used to modify the shape of the solitary pulse instead of adding higher order dissipation terms to the equations. This study may be useful to construct the compressive and rarefactive electrostatic potential pulses associated with the broadband electrostatic noise type emissions.

Excitation of the geodesic acoustic mode continuum by drift wave turbulence is studied using the wave kinetic approach. For a model profile of weak non-uniform ion temperature, the forms of growth rate and radial structure of geodesic acoustic modes are obtained analytically. The growth rate is analyzed for several conditions for present-day tokamaks and compared with that for uniform ion temperature, as well as that given by the coherent mode approach for non-uniform ion temperature.

Arbitrary amplitude dust-acoustic double-layers (DA-DLs) in two high-energy tail ion distributions are investigated. The electron number density has been assumed sufficiently depleted during the charging of dust grains on account of the attachment of background plasma electrons on the surface of dust grains. It is found that under certain conditions DA-DLs may be admitted. The degree of suprathermality of the low-temperature component has a sensitive role on their formation and a small change in this degree can even prevent the DL formation. The ‘Maxwellianization’ of the high-temperature component involves a suprathermalization process of the low-temperature component for the existence of localized DA-DLs. Our results may be relevant to a number of space dusty plasma systems, particularly the Saturn's F-ring where electron depletion and suprathermality are thought to come into play.

The double tearing mode (DTM) instability with two qs = 1 rational surfaces is investigated by taking into account the collisionless effects, including electron inertia and electron viscosity in a cylindrical geometry. The calculations show that for q-profile with a small distance between two rational surfaces, Δrs, there exists a broad linear spectrum of collisionless DTMs. The collisionless effects not only can significantly increase the linear growth rate of DTMs but can also enlarge the width of spectrum of unstable modes. For the q-profile with fixed Δrs and fixed magnetic shears at two rational surfaces, the high-order harmonics with smaller wavelength, such as the m/n = 2/2, 3/3 and 4/4 modes, can be easily excited to have larger growth rates than the m/n = 1/1 mode by ‘lifting’ the safety factor value between two rational surfaces. The characteristics of eigenmode structures of the most unstable and secondly unstable DTMs with various mode numbers are analyzed in detail and the corresponding collisionless scalings are numerically obtained and verified theoretically based on the previous relevant analytical theories. In addition, the synergetic effects of plasma resistivity, electron inertia and electron viscosity on the linear growth rates of DTMs are analyzed.

A one-dimensional fluid model is built to study the effect of radio frequency (RF) on the characteristics of RF nitrogen discharge with induced argon plasma at high pressure. The model is solved by a finite difference method, and the numerical results are obtained. The numerical results show that by modulating driven frequency, the discharge can obtain higher plasma density. Moreover, the discharge is operated in a stable α mode in a range of 100 MHz of driven frequency.

The dust-ion-acoustic solitary waves (DIA SWs) in an unmagnetized dusty plasma containing non-thermal electrons, cold mobile positive ions, and stationary arbitrarily (positively and negatively) charged static dust have been theoretically studied. The reductive perturbation technique has been employed to derive the Korteweg-de Vries equation, which admits SW solutions under certain conditions. It has been also shown that the basic features (amplitude, width, speed, etc.) of DIA SWs are significantly modified by the polarity of dust and non-thermal electrons. The implications of our results in space and laboratory dusty plasma situations are briefly discussed.

A theoretical investigation has been made of the linear propagation of different electromagnetic modes in a dense electron–ion magnetoplasma containing degenerate electrons and ions. The fluid model and the normal mode analysis have been employed. It has been found that the dispersion properties of the electromagnetic waves propagating in such a degenerate plasma are different (in view of both spatial and temporal scales) from those propagating in the usual electron–ion plasma because of the effects of degenerate plasma pressure, enthalpy, etc. The importance of this work has been discussed also.