Free-boundary plasma equilibria with toroidal plasma flows

Magnetohydrodynamic equilibrium schemes with toroidal plasma flows and the scrape-off layer are developed for the 'divertor-type' and 'limiter-type' free boundaries in the tokamak cylindrical coordinator. With a toroidal plasma flow, the flux functions are considerably different under the isentropic and isothermal assumptions. The effects of the toroidal flow on the magnetic axis shift are investigated. In a high beta plasma, the magnetic shift due to the toroidal flow are almost the same for both the isentropic and isothermal cases, and are about 0.04a0 (a0 is the minor radius) for M0=0.2 (the toroidal Alfvѐn Mach number on the magnetic axis). In addition, the X-point is slightly shifted upward by 0.0125 a0. But the magnetic axis and the X-point shift due to the toroidal flow may be neglected because M0 is usually less than 0.05 in a real tokamak. The effects of the toroidal flow on the plasma parameters are also investigated. The high toroidal flow shifts the plasma outward due to the centrifugal effect. Temperature profiles are noticeable different because the plasma temperature is a flux function in the isothermal case.

Turbulence and Particle Acceleration in a Relativistic Plasma

In a collisionless plasma, the energy distribution function of plasma particles can be strongly affected by turbulence. In particular, it can develop a nonthermal power-law tail at high energies. We argue that turbulence with initially relativistically strong magnetic perturbations (magnetization parameter σ ≫ 1) quickly evolves into a state with ultrarelativistic plasma temperature but mildly relativistic turbulent fluctuations. We present a phenomenological and numerical study suggesting that in this case, the exponent α in the power-law particle-energy distribution function, f(γ)d γ ∝ γ −α d γ, depends on magnetic compressibility of turbulence. Our analytic prediction for the scaling exponent α is in good agreement with the numerical results.

Vacuum System Optimization for EAST Neutral Beam Injector

The neutral beam injector (NBI) generates a high-energy ion beam and neutralizes it, and then relies on drift transmission to inject the formed neutral beam into the fusion plasma to increase the plasma temperature and drive the plasma current. In order to better cooperate with the Experimental Advanced Superconductive Tokamak (EAST), part of the Chinese major national scientific and technological infrastructure, in carrying out long-pulse high-parameter physics experiments of 400 s and above, this paper considers the optimization of the current design and operation of the NBI beam line with a pulse width of 100 s. Based on an upgraded and optimized NBI vacuum chamber and the structure of the beam-line components, the gas-source characteristics under the layout design of the NBI system are analyzed and an NBI vacuum system that meets relevant needs is designed. Using Molflow software to simulate the transport process of gas molecules in the vacuum chamber, the pressure gradient in the vacuum chamber and the heat-load distribution of the low-temperature condensation surface are obtained. The results show that when the NBI system is dynamically balanced, the pressure of each vacuum chamber section is lower than the set value, thus meeting the performance requirements for the NBI vacuum system and providing a basis for subsequent implementation of the NBI vacuum system upgrade using engineering.

The Propagation Properties of a Laguerre–Gaussian Beam in Nonlinear Plasma

The self-focusing properties of the Laguerre-Gaussian (LG) beam in nonlinear plasma, characterized by significant collisional or ponderomotive nonlinearity have been explored. The second-order differential equation of the beam width is established from Maxwell’s equations with Wentzel–Kramers–Brillouin (WKB) and paraxial like approximation. The effect of the vortex charge number, intensity parameter and plasma temperature on the self-focusing properties of the Laguerre-Gaussian beam has been investigated.

Plasma Gas Temperature Control Performance of Metal 3D-Printed Multi-Gas Temperature-Controllable Plasma Jet

The aim of the study was to design and build a multi-gas temperature-controllable plasma jet that can control the gas temperature of plasmas with various gas species, and evaluated its temperature control performance. In this device, a fluid at an arbitrary controlled temperature is circulated through the plasma jet body. The gas exchanges heat with the plasma jet body to control the plasma temperature. Based on this concept, a complex-shaped plasma jet with two channels in the plasma jet body, a temperature control fluid (TCF) channel, and a gas channel was designed. The temperature control performance of nitrogen gas was evaluated using computational fluid dynamics analysis, which found that the gas temperature changed proportionally to the TCF temperature. The designed plasma jet body was fabricated using metal 3D-printer technology. Using the fabricated plasma jet body, stable plasmas of argon, oxygen, carbon dioxide, and nitrogen were generated. By varying the plasma jet body temperature from −30 °C to 90 °C, the gas temperature was successfully controlled linearly in the range of 29–85 °C for all plasma gas species. This is expected to further expand the range of applications of atmospheric low temperature plasma and to improve the plasma treatment effect.

Bunch Expansion as a Cause for Pulsar Radio Emissions

Electromagnetic waves due to electron–positron clouds (bunches), created by cascading processes in pulsar magnetospheres, have been proposed to explain the pulsar radio emission. In order to verify this hypothesis, we utilized for the first time Particle-in-Cell (PIC) code simulations to study the nonlinear evolution of electron–positron bunches dependant on the initial relative drift speeds of electrons and positrons, plasma temperature, and distance between the bunches. For this sake, we utilized the PIC code ACRONYM with a high-order field solver and particle weighting factor, appropriate to describe relativistic pair plasmas. We found that the bunch expansion is mainly determined by the relative electron–positron drift speed. Finite drift speeds were found to cause the generation of strong electrostatic superluminal waves at the bunch density gradients that reach up to E ∼ 7.5 × 105 V cm−1 (E/(m e c ω p e −1) ∼ 4.4) and strong plasma heating. As a result, up to 15% of the initial kinetic energy is transformed into the electric field energy. Assuming the same electron and positron distributions, we found that the fastest (in the bunch reference frame) particles of consecutively emitted bunches eventually overlap in momentum (velocity) space. This overlap causes two-stream instabilities that generate electrostatic subluminal waves with electric field amplitudes reaching up to E ∼ 1.9 × 104 V cm−1 (E/(m e c ω p e −1) ∼ 0.11). We found that in all simulations the evolution of electron–positron bunches may lead to the generation of electrostatic superluminal or subluminal waves, which, in principle, can be behind the observed electromagnetic emissions of pulsars in the radio wave range.

Control of plasma spatial distribution in gas discharge lamps filled with alkali metal vapors

The thermodynamic properties of alkali metal vapor plasma in the pressure range 0.25 - 3.0 atm and temperatures 1500 - 60000 K are considered. It is shown that a distinctive feature of this plasma is the existence of a relatively narrow critical temperature interval in which the plasma consists only of electrons and singly ionized atoms. The specific heat capacity of the plasma has a minimum value in the critical temperature range, corresponding to the heat capacity of a simple e-i plasma in which the second ionization of atoms has not begun. It has been shown that, due to this property, in gas discharge lamps filled with alkali metal vapors, it is possible to control the type of spatial distribution of the plasma. Under relatively low currents, when the temperature of the plasma doesn’t reach the critical range of the value, the traditional space distribution of the plasma is realized in the gas discharge tube. In this case, most of the plasma is concentrated in the axial region of the tube and its concentration decreases along the radius from the axis to the walls of the tube. With sufficiently high currents, when the plasma temperature on the axis exceeds the values from the critical interval, the opposite case is realized: the main part of the plasma is now concentrated on the periphery of the gas discharge volume. In this case, the plasma concentration increases along the radius from the axis to the tube walls. It is shown that the transformation of one type of spatial distribution of plasma into another occurs when the plasma temperature on the axis reaches values from the critical interval and the specific heat capacity approaches its minimum value, corresponding to a simple plasma consisting of electrons and single-charge ions.

Experimental Study of the Effect of Plasma Cutting on the Tensile Strength of Materials "Fe"

The cutting process in plasma cutting begins with the formation of a pilot arc between the electrode and the workpiece as a result of the electrical ionization reaction of the highly conductive cutting gas. The gas is heated by the pilot arc until its temperature rises very high then the gas will be ionized and become a conductor of electricity. When the gas stream leaves the nozzle, the gas expands rapidly carrying the molten metal so that the cutting process continues. This plasma temperature can reach 33,000°C, approximately 10 times the temperature produced by the reaction of oxygen and acetylene. If this is related to the mechanical properties of the material, where the material has been heated it will result in changes in the mechanical properties of the material in the heating area/around the cutting plane. Tensile testing is the most widely used type of test because it is able to provide representative information on the mechanical behavior of the material. Seeing an incident like this, it is necessary to test the Effect of Plasma Cutting on the Tensile Strength of 'Fe' Materials through a tensile test. Several studies have shown that torch height, amperage and cutting speed can affect material properties. The best tool parameter settings are obtained at a travel speed of 500 mm/min, 75 amperes and a torch-material distance of 3 mm so that these settings are used as a reference in this study. In analyzing the data, the authors compare the results of plasma cutting testing with conventional cutting, in order to know the changes in mechanical properties that occur.

On physical investigation of ball lightnings

Explanations for the long lifetime of spherically symmetric objects in nature and the short lifetime of laboratory plasma are given. A qualitative description of the relativistic model of ball lightning is also given, which is a spherical electric region with strong electric and magnetic fields. The plasma temperature in the zone of the ball-lightning generation is measured by the spectroscopic method. A large ball lightning, the maximum diameter of which is equal to one meter and which stands in the region of its generation, is also registered after the formation and departure of a high-energy ball lightning. The reason for the low emissive power in the optical range characteristic for the atmospheric ball lightning is explained by the absence of electron transitions in the outer proton-containing shell. The absence of electrical breakdown at ultrahigh electric field between the core and the outer shell of the ball lightning and its destruction at the moment when the resulting force becomes nonzero are also explained.

Investigation of Shielding Effects on Picosecond Laser-Induced Copper Plasma Characteristics under Different Focusing Distances

In traditional laser-induced breakdown spectroscopy (LIBS) applications, the line intensity and analysis capability are susceptible to plasma shielding. To investigate the shielding effects on the characteristics of Cu plasma in air, a ~120-picosecond laser with a wavelength of 1064 nm was employed to produce plasma. The plasma temperature and electron density were calculated under the condition of local thermal equilibrium (LTE) and optically thin, while the relationships between the line intensity, plasma temperature and electron density were analyzed. Moreover, the LTE condition was validated by the McWhirter relation, plasma relaxation time and diffusion length, and the optically thin condition was observed through the variation in line intensity. The results indicated that when the focal point was below the target surface, the plasma shielding was the weakest, and the highest line intensity could be obtained. In addition, there was a positive correlation between the increased plasma temperature and the degree of shielding effect. When the focal point was above the target surface, the high-irradiance pulse directly broke down the free air and produced a shock wave. Under the high pressure of the over-heated shock wave, the line intensity, plasma temperature and electron density increased again. This study provides an important insight into the experiments and applications of picosecond LIBS.