Beam Plasma Research Articles

Studies of growing waves in Hall thruster beam plasma under the influence of electron temperature

Studies of growing waves in Hall thruster beam plasma under the influence of electron temperature

Third and Fourth Harmonics of Electromagnetic Emissions by a Weak Beam in a Solar Wind Plasma with Random Density Fluctuations

Electromagnetic emissions and at the third and fourth harmonics of the plasma frequency ω p were observed during the occurrence of type II and type III solar radio bursts. Two-dimensional particle-in-cell simulations are performed using a weak beam, high space and time resolutions, and a plasma with density fluctuations of a few percent, for parameters relevant to regions of type III bursts. For the first time, a detailed study of the different wave coalescence processes involved in the generation of and waves is presented and the impact of density fluctuations on the wave interaction mechanisms is demonstrated. Energy ratios between the second, third, and fourth harmonics , , and are consistent with space observations. It is shown that, in both homogeneous and inhomogeneous plasmas, the dominant processes generating () are the coalescence of () with a Langmuir wave, in spite of the random density fluctuations modifying the waves’ resonance conditions by energy transport in the wavevector space and of the damping of Langmuir waves. The role of the backscattered (forward-propagating) Langmuir waves coming from the first (second) cascade of the electrostatic decay of beam-driven Langmuir waves is determinant in these processes. Understanding such wave coalescence mechanisms can provide indirect information on Langmuir and ion acoustic wave turbulence, the average level of density inhomogeneities, and suprathermal electron fluxes generated in solar wind regions where the harmonics manifest. Causes for the rarity of their observations are discussed.

Improved treatment of home-made glow discharge ion source

For a better treatment, a new class of DC ion source (DCIS) was developed and adapted to provide low-power, highly-density plasma and ion-current applications. Such an ion source operates under the mode of abnormal glow discharge being of the self-extraction category, with specific features such as simple operation, stable discharge, and the ability to use for a variety of plasma, ion, and electron beam applications. A teflon disc with different diameters has been installed in between the two electrodes. This disc covered the cathode area, reducing the discharge area on the cathode surface for discharge confinement, and thus allowing for a higher output ion beam current. Pressures of 10−4 mbar, a 3 mm gap between the electrodes, and a 5 mm teflon diameter were observed to be the optimal operating conditions. At this ideal distance, hydrogen, nitrogen, and argon gases were used to investigate internal and external operational parameters. Finally, the Paschen curves were determined for hydrogen, air, as well as nitrogen gases.

Relativistic-ponderomotive effect on the self-focusing of a high-intensity cosh-Gaussian laser beam in plasma: higher-order paraxial regime

Relativistic-ponderomotive effect on the self-focusing of a high-intensity cosh-Gaussian laser beam in plasma: higher-order paraxial regime

Proton beam-driven instabilities in an inclined magnetic field

In this paper, the electrostatic and electromagnetic instabilities of a magnetized proton–DT plasma relevant to the fast ignition scheme of inertial fusion were examined. The magnetic field and proton beam define a plane and the magnetic field vector has the orientation angle of θ. The dispersion relation of two-stream and filamentation modes was first derived using the conservation, Euler, and Maxwell equations. Then, the more general case describing the wave propagation in an arbitrary direction in the two-dimensional case was derived symbolically. It is demonstrated that in a magnetized beam–plasma system, the two-stream instability depicts two separated growth curves, one larger than the other and there exists a stable frequency band between them. This zone will grow as the magnetic field inclination angle increases such that the smaller two-stream peak vanishes at the limiting angle of θ→π/2. The splitting in the growth rate curve becomes obvious at magnetic field parameter Ωe>0.5. The pure filamentation instability of the beam–plasma is about two orders of magnitude smaller than the two-stream instability and it just contributes to magnetic field orientation θ=0. In a two-dimensional case, the mixed electrostatic/electromagnetic instabilities contribute to the final growth rate curve producing an X-like shape. The interface point of two growth curves is characterized by coordinate (∼1.0, tan(θ)) in the zx-plane.

Upper hybrid wave excitation and particle acceleration by resonant beating of two hollow Gaussian laser beams in magnetized plasma

This paper investigates the excitation of the upper hybrid wave by resonant beating of two intense hollow Gaussian relativistic laser beams in a magnetized plasma. Hollow laser beams are taken in this study because they have the same power at different beam orders. The interaction of two intense hollow laser beams at the frequency difference ( Δ ω ≈ ω 1 − ω 2 ) and wavenumber ( Δ k = k 1 − k 2 ) excites the upper hybrid wave in the magnetized plasma. The excited upper hybrid wave accelerates the electrons to higher energies. The acceleration of electrons has also been studied. This study is carried out under a higher-order paraxial region, where the dielectric constant and the eikonal are expanded to the fourth power of the radial distance. Analytical expressions are obtained for the beam width parameter of the hollow Gaussian laser beams, the electric field of the upper hybrid wave, and the energy gain by the electrons. The effects of various laser and plasma parameters (such as beam order, plasma frequency, and electron cyclotron frequency) on the electric field of the upper hybrid wave and the energy gain of electrons have been explored. The results are compared with paraxial region and the Gaussian profile of laser beams. Numerical analysis has been performed for well-established laser and plasma parameters.

Generation of beam plasma near a dielectric target irradiated by a pulsed large-radius electron beam in the forevacuum pressure range

We have investigated generation of beam plasma near a dielectric (ceramic) target irradiated by a pulsed large-radius electron beam in the forevacuum pressure range 3–15 Pa. The electron beam was accelerated with voltage up to 8 kV. Under a certain threshold accelerating voltage increase in the plasma density was observed near the dielectric target as compared with beam plasma density without the target. A decrease in gas pressure leads to smaller value of this threshold voltage. The observed dependencies are apparently caused by two factors: secondary electrons being emitted from the ceramic target and charging of surface of the ceramic target by the e-beam. The secondary electrons, emitted from the ceramic target, provide “additional” ionization of the gas. The charge on the dielectric target surface creates a field that accelerates the slow secondary electrons, which provides an increase in plasma density near the ceramic target. The negative charge on the target slows down the beam electrons, and thus increases total ionization cross section of gas by electron impact. The value of negative charge on the dielectric surface increases with decreasing gas pressure.

High power terahertz radiation generated by beam-plasma system in multi-filament regime

In the particle-in-cell simulation study of this paper, it is found that the high-power terahertz radiation at twice the plasma frequency can be generated by the interaction between a weakly relativistic, large-radius, focused electron beam and an overdense plasma. The terahertz radiation is emitted from a multi-filament structure in the electron beam, which is caused by the coupling of the longitudinal two-stream instability and the transverse filamentation instability. The analysis of the k space of the plasma waves indicates that the radiation can be explained by the mode coupling among a forward oblique mode, a backward oblique mode, and a second harmonic radiation mode. The influences of the beam Lorentz factor and plasma density on the radiation power, efficiency, and coherence are also investigated. The present results not only contribute to the development of novel megawatt-level narrowband terahertz radiation sources, but also propose a potential terahertz radiation mechanism for the fundamental research of the beam-plasma system.

Measurement of mass-to-charge beam plasma ion composition during electron beam evaporation of refractory materials in the forevacuum pressure range

We describe here the design of the modernized ion-optical system (IOS) of the standard residual gas analyzer (RGA). IOS electrodes are made of stainless steel. The electrodes are powered outside the vacuum chamber. Reducing the diameter of the entrance aperture to 0.6 mm made it possible to expand the measurement range. These design features of this system makes it possible to measure the mass-to-charge composition of beam plasma ions generated by electron beam evaporation of ceramics and refractory metals in the forevacuum pressure range under a prolonged exposure to high temperature. We present the results of the measured plasma composition during evaporation of aluminum oxide and zirconium ceramics, as well as of titanium.

Effect of Asymmetry in the Modulation Parameters on Self-Focusing of Asymmetric Finite Airy-Gaussian Laser Beam in Collisionless Plasma

The self-focusing/defocusing of asymmetric finite Airy-Gaussian (AiG) laser beam has been investigated by employing standard Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations in a nonrelativistic regime for underdense plasma. The second-order non-linear coupled differential equations have been solved numerically by using the fourth-order Range-Kutta method. The effect of asymmetry in the modulation parameters on the self-focusing/defocusing of the asymmetric finite AiG laser beam in collisionless plasma has been studied. It is observed that the self-focusing/ defocusing of asymmetric finite AiG laser beam is strongly connected with the initial values of the laser and plasma parameters such as modulation parameters and plasma frequency.

Increased Water-Soluble Yellow Monascus Pigment Productivity via Dual Mutagenesis and Submerged Repeated-Batch Fermentation of Monascus purpureus.

Monascus pigments (MPs) have been used in the food industry for more than 2,000 years and are known for their safety, bold coloring, and physiological activity. MPs are mainly yellow (YMPs), orange (OMPs), and red (RMPs). In this study, a mutant strain Monascus purpureus H14 with high production of water-soluble YMPs (WSYMPs, λmax at 370 nm) was generated instead of primary YMPs (λmax at 420 nm), OMPs (λmax at 470 nm), and RMPs (λmax at 510 nm) produced by the parent strain M. purpureus LQ-6 through dual mutagenesis of atmospheric and room-temperature plasma and heavy ion beam irradiation (HIBI), producing 22.68 U/ml extracellular YMPs and 10.67 U/ml intracellular YMPs. WSYMP production was increased by 289.51% in optimal conditions after response surface methodology was applied in submerged fermentation. Application of combined immobilized fermentation and extractive fermentation improved productivity to 16.89 U/ml/day, 6.70 times greater than with conservative submerged fermentation. The produced WSYMPs exhibited good tone stability to environmental factors, but their pigment values were unstable to pH, light, and high concentrations of Ca2+, Zn2+, Fe2+, Cu2+, and Mg2+. Furtherly, the produced exYMPs were identified as two yellow monascus pigment components (monascusone B and C21H27NO7S) by UHPLC-ESI-MS. This strategy may be extended to industrial production of premium WSYMPs using Monascus.

High-energy proton beam acceleration driven by an intense ultrarelativistic electron beam in plasma

We report a generation of energetic protons by the interaction of a high-energy electron driving beam with an underdense plasma slab. After an interaction period of approximately 4000 fs, a proton beam with maximum energy greater than 250 MeV can be achieved by applying a driving beam with energy 1.0 GeV to a 200 $\mathrm {\mu }$ m plasma slab. Our two-dimensional particle-in-cell simulations also show that the proton acceleration process can be divided into two stages. In the first stage, a strong positive longitudinal electric field appears near the rear boundary of the plasma slab after the driving beam has passed through it. This acceleration process is similar to the target normal sheath acceleration scheme by the interaction between intense pulsed laser with overdense plasma targets. In the second stage, the accelerated protons experience a long-range acceleration process with a two-stream instability between the high-energy driving beam and the proton beam. Further analyses show that this accelerated proton beam is equipped with the property of good collimation and high energy. This scheme presents a new way for proton or ion acceleration on some special occasions.

Electron Acoustic Peregrine Breathers in a Quantum Plasma With 1-D Temperature Anisotropy

In the work, we study the formation of electron acoustic Korteweg–de Vries (KdV) solitons and their gradual nonlinear evolution into a peregrine soliton (PS) in a dense plasma at finite temperature with quantum effects. The plasma under consideration has temperature anisotropy along the direction of wave propagation. Such an anisotropy is due to the initial disturbance incorporated in the system or due to the lack of homogeneity of field quantities. We have studied both the linear and nonlinear characteristics of their dispersion relation. By employing reductive perturbation technique, we have obtained the KdV equation and studied the characteristics of the solitary structures. The effect of external forcing term which leads to self-interaction among different parts of the system and the gradual conversion of the waveform into Peregrine breather mode is analytically studied. Finally, we study the dynamical properties of the system and its dependence on plasma parameters. This theoretical study will help in predicting possible characteristics in laser plasma interaction and beam plasma experiments in which there are instances of temperature anisotropy.

Rogue Wave Generation Through Nonlinear Self-Interaction of Electrostatic Waves in Dense Plasma

In this work, we start with the quantum hydrodynamic model equations for two temperature-populated electrons in a dense plasma with quantum effects. We obtain the KdV equation for the electron acoustic (EAW) mode. The EAW self-interacts to form a rogue wave-type envelop soliton which is described by the nonlinear Schrodinger (NLS) equation. To study the stability criteria, we transform the KdV and NLS equations into its dynamical system counterparts and analyze the phase portraits and carry out the bifurcation analysis. The possibility of hyperchaos is discussed with reference to rogue waves. The finding will be helpful in laser plasma interactions, microelectronics, as well as beam plasma physics and fusion technology.

Assessments of the performance of neutral beam injection on the spherical tokamak EXL-50

The numerical simulation of the neutral beam injection (NBI) heating in the spherical tokamak EXL-50 has been performed in order to offer a guideline for the practicable engineering design. A series of parameter scans on injected beam energy, plasma density, electron temperature, plasma current and injection direction have been performed with the NBI heating analysis code NUBEAM. The simulation results show that the injected beam energy should be matched with the plasma density to avoid the excessive shine-through loss. For the scenario with central plasma density of 3.0 × 1019 m−3, the 20 keV beam injection has a power absorption rate about 77%, while for the 50 keV beam injection, only 57% injected power has been absorbed by plasma. When the central plasma density increases to 5.0 × 1019 m−3, a power absorption rate more than 70% can be obtained even for the 50 keV beam injection. As the increase in the electron temperature, the injected power is more likely to heat ions while the total absorbed power by plasma roughly remains stable. The increased plasma current leads to the stronger poloidal magnetic field. A qualitative elucidation on the fast ion trajectory has been given to reveal that the orbit loss has been remarkably suppressed by the enhanced poloidal magnetic field. In addition, a comparison of power absorption rate in the co-current and counter-current injection cases has been carried out, which suggests that counter-current injection leads to more orbit loss and hence less power absorption rate.

Combined effect of transverse electric and magnetic fields on THz generation by beating of two amplitude-modulated laser beams in the collisional plasma

Combined effect of transverse electric and magnetic fields on THz generation by beating of two amplitude-modulated laser beams in the collisional plasma

Ion Composition of the Beam Plasma Generated by Electron-Beam Evaporation of Metals and Ceramic in the Forevacuum Range of Pressure

We present the results of measurements of the ion composition of the plasma generated by an accelerated electron beam in the forevacuum pressure range. It has been found that the main contribution to ionization processes comes from beam electrons. It has been shown that, during the electron-beam evaporation of metal or ceramic targets, the number of ions evaporated from the materials in the beam plasma significantly exceeds the number of ions produced from the residual atmosphere and admitted gases. Together, electron beams and beam-produced plasma can catalyze the processes of coatings deposition or modification of the surface layer of the samples.

The propagation properties of a Laguerre–Gaussian beam in nonlinear plasma

The self-focusing properties of the Laguerre–Gaussian beams 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 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.

Excitation of ion acoustic waves by self-focused q-Gaussian laser beam in plasma with axial density ramp

Excitation of ion acoustic waves by self-focused q-Gaussian laser beam in plasma with axial density ramp

A Report on the Modelling, Design and Fabrication of Polymer Modulators

Polymer modulators based on Mach-Zehnder interferometers were designed, modelled, fabricated, and tested in this project. Built on a silicon-on-insulator wafer with 220 nm active silicon width, electron beam lithography, plasma etching, metal deposition and lift-off, and polymer deposition were used in the fabrication process. The simulated waveguide group index is 4.377 at 1.55 m, the estimated r33 of the polymer modulator is 8.46 pm/V and the V is 908 V. The measured group index is 4.541, indicating the fabricated feature size is smaller than the design.