Magnetic Force-Free Theory: Nonlinear Case

In this paper, a theory of force-free magnetic field useful for explaining the formation of convex closed sets, bounded by a magnetic separatrix in the plasma, is developed. This question is not new and has been addressed by many authors. Force-free magnetic fields appear in many laboratory and astrophysical plasmas. These fields are defined by the solution of the problem ∇×B=ΛB with some field conditions B∂Ω on the boundary ∂Ω of the plasma region. In many physical situations, it has been noticed that Λ is not constant but may vary in the domain Ω giving rise to many different interesting physical situations. We set Λ=Λ(ψ) with ψ being the poloidal magnetic flux function. Then, an analytic method, based on a first-order expansion of ψ with respect to a small parameter α, is developed. The Grad–Shafranov equation for ψ is solved by expanding the solution in the eigenfunctions of the zero-order operator. An analytic expression for the solution is obtained deriving results on the transition through resonances, the amplification with respect to the gun inflow. Thus, the formation of Spheromaks or Protosphera structure of the plasma is determined in the case of nonconstant Λ.

Theoretical study of the Alfven Eigenmode stability in CFETR steady state discharges

The aim of this study is to analyze the stability of Alfven Eigenmodes (AE) in the China Fusion Engineering Test Reactor (CFETR) plasma for steady state operations. The analysis is done using the gyro-fluid code FAR3d including the effect of the acoustic modes, EP Finite Larmor radius damping effects and multiple energetic particle populations. Two high poloidal β scenarios are studied with respect to the location of the internal transport barrier (ITB) at r/a ≈ 0.45 (case A) and r/a ≈ 0.6 (case B). Both operation scenarios show a narrow TAE gap between the inner-middle plasma region and a wide EAE gap all along the plasma radius. The AE stability of CFETR plasmas improves if the ITB is located inwards, case A, showing AEs with lower growth rates with respect to the case B. The AEs growth rate is smaller in the case A because the modes are located in the inner-middle plasma region where the stabilizing effect of the magnetic shear is stronger with respect to the case B. Multiple EP populations effects (NBI driven EP + alpha articles) are negligible for the case A, although the simulations for the case B show a stabilizing effect of the NBI EP on the n=1 BAE caused by alpha particles during the thermalization process. If the FLR damping effects are included in the simulations, the growth rate of the EAE/NAE decreases up to 70 %, particularly for n > 3 toroidal families. Low n AEs (n<6) show the largest growth rates. On the other hand, high n modes (n=6 to 15) are triggered in the frequency range of the NAE, strongly damped by the FLR effects.

LANGMUIR PROBE TO CHARACTERIZE THE DUST PLASMA OF ALUMINUM OXIDE (AL2O3) PRODUCED BY DC PLASMA SYSTEM

In this research, we have conducted an experimental study of the dusty plasma to the Aluminum oxide (Al2O3) dust material with a grain radius of (0.2) µm to (0.6) µm. In the experiment, we use air in the vacuum chamber system under different low pressure (0.1-0.8) Torr. The results have showed that the existence of dust particles in air plasma is equal to the Paschen minimum which is (0.4) Torr with Al2O3 dusty and without dust. The effect of Al2O3 dust particles on the plasma characteristics like floating potential (Vf), plasma potential (Vp), electron saturation current (Ies), temperature of the electron (Te), density of electron (ne) and density of ion (ni) of the DC system that can be calculated in the glow-discharge region. Parameter measurements are taken by four cylindrical probes which are diagnosed at a distance of (40) mm from the cathode diameter, the Paschen minimum at a pressure of (0.4) Torr. The plasma potential and the probe's floating voltage become more negative when dust is immersed in the plasma region. The features of these parameters show that the current discharge decreases while the discharge voltage increases when the aluminum oxide dust particles that are incorporated. And vice versa was in the absence of dust. Electron density increases in the existence of dust particles which causes the electron temperature to decrease.

EVALUATION OF GROWTH AND SEED YIELD OF TWO CULTIVARS OF FLAX

In this research, we have conducted an experimental study of the dusty plasma to the Aluminum oxide (Al2O3) dust material with a grain radius of (0.2) µm to (0.6) µm. In the experiment, we use air in the vacuum chamber system under different low pressure (0.1-0.8) Torr. The results have showed that the existence of dust particles in air plasma is equal to the Paschen minimum which is (0.4) Torr with Al2O3 dusty and without dust. The effect of Al2O3 dust particles on the plasma characteristics like floating potential (Vf), plasma potential (Vp), electron saturation current (Ies), temperature of the electron (Te), density of electron (ne) and density of ion (ni) of the DC system that can be calculated in the glow-discharge region. Parameter measurements are taken by four cylindrical probes which are diagnosed at a distance of (40) mm from the cathode diameter, the Paschen minimum at a pressure of (0.4) Torr. The plasma potential and the probe's floating voltage become more negative when dust is immersed in the plasma region. The features of these parameters show that the current discharge decreases while the discharge voltage increases when the aluminum oxide dust particles that are incorporated. And vice versa was in the absence of dust. Electron density increases in the existence of dust particles which causes the electron temperature to decrease.

Redistribution of Energy during Interaction of a Shock Wave with a Temperature Layered Plasma Region at Hypersonic Speeds

The paper is devoted to the problem of the interaction between a shock wave and a thermally stratified energy source for the purpose of supersonic/hypersonic flow control realization. The effect of the thermally stratified energy source on a shock wave with the Mach number in the range of 6–12 is researched numerically based on the Navier-Stokes system of equations. Redistribution of specific internal energy and volume density of kinetic energy behind the wave front is investigated. Multiple manifestations of the Richtmyer-Meshkov instability has been obtained which has caused the blurring and disappearance of shock wave and contact discontinuity fronts in density fields. A study of the efficiency of using a stratified energy source instead of a homogeneous one with the same value of the full energy is carried out. The agreement with the available experimental data for the shock wave Mach number 6 has been obtained.

Harmonic generation in the interaction of laser with a magnetized overdense plasma

The mechanism of harmonic generation in both O- and X-mode configurations for a magnetized plasma has been explored here in detail with the help of particle-in-cell simulations. A detailed characterization of both the reflected and transmitted electromagnetic radiation propagating in the bulk of the plasma has been carried out for this purpose. The efficiency of harmonic generation is shown to increase with the incident laser intensity. A dependency of harmonic efficiency has also been found on magnetic field strength. This work demonstrates that there is an optimum value of the magnetic field at which the efficiency of harmonic generation maximizes. The observations are in agreement with theoretical analysis. For the O-mode configuration, this is compelling as the harmonic generation provides for a mechanism by which laser energy can propagate inside an overdense plasma region.

Influence of solution properties and gas addition on hydrogen peroxide production by a novel plasma source

The paper evaluates concentration of hydrogen peroxide produced by a novel pin-hole plasma source in electrolyte solutions with or without gas addition. An effective production rate of hydrogen peroxide is decreased by the increased argon as well as oxygen flow rate through the plasma region. Further, it is enhanced by higher solution conductivity while it is decreased in the strongly basic conditions with the highest pH values.