Cylindrical Plasma Research Articles

Determination of atomic hydrogen density and fluorescence decay time by 1D resolved, picosecond TALIF in the RAID linear device

Abstract We report on the first 1D resolved two-photon absorption laser-induced
fluorescence (TALIF) measurements of atomic hydrogen (H) performed in the
Resonant Antenna Ion Device (RAID) using a picosecond laser system. The
results are obtained across a cylindrical plasma column with peak electron
density 10^18 m^-3 and temperature 1 eV on axis, which decrease monotonically
to 2*10^17 m^-3 and 0.75 eV over a scale of a few cm away from the axis. TALIF
results in these conditions are compatible with a uniform H density profile across
the observed region, with a mean dissociation degree close to 3%. The small
variation of H density across regions covering a wide range of plasma parameters
suggests that transport processes and wall interactions play an important role in
determining the H density profile. The fluorescence decay time is close to 10 ns at
all observed locations, a result compatible with complete substate mixing of the
n = 3 states of H.

Influence of electrode transparency on the plasma properties of a cylindrical IEC plasma source

This study investigates the influence of cathode and anode grid transparency on the plasma properties of a Cylindrical Inertial Electrostatic Confinement plasma source. The primary focus is to elucidate how variations in the transparency of the electrodes impact plasma characteristics and the operational performance of the source, particularly during spray jet mode. Employing optical emission spectroscopy (OES) and Langmuir probe diagnostics, the plasma behavior is analyzed comprehensively. The results demonstrate that cathode transparency has a pronounced effect on discharge current and plasma density within the cathode. Conversely, the transparency of the anode has only a little influence the ignition characteristics and operational stability of the plasma source. The findings highlight the importance of utilizing cathode transparency to adjust both the pressure and voltage operating ranges of the IEC source in spray jet mode, optimizing its performance for various applications.

Enhanced degradation of aqueous caffeine via cylindrical dielectric barrier discharge plasma: Efficacy and toxicity insights

An environmentally friendly approach for caffeine degradation was explored in this study utilizing cylindrical dielectric barrier discharge (CDBD) plasma. The current-voltage characteristics and the plasma parameters of the CDBD, such as the electron temperature, electron density, density of nitrogen excited states, vibrational temperature, and rotational temperature, were assessed through electrical and optical characterization respectively. Fourier-transform infrared spectroscopy (FTIR) was employed to evaluate the reactive oxygen and nitrogen species (RONS) in the plasma-treated air. The physicochemical properties of deionized water (DW) were measured. To gain a deeper insight into the role of RONS in caffeine degradation, their concentrations in DW were analyzed. Furthermore, the effects of initial concentration, sample volume, and pH on caffeine degradation were investigated. The highest degradation of caffeine was 94% at initial concentration of 50 mg L-1, sample volume 50 mL and in neutral pH. Liquid chromatography–mass spectrometry (LC-MS) was then used to propose the degradation pathway for caffeine. The major reactive species involved in caffeine degradation was ozone. Finally, the phytotoxicity and cytotoxicity of caffeine were assessed before and after plasma treatment with plasma-treated caffeine (PTC) showing minimal toxicity to both plants and cells.

Plasma centrifugation method for separation of the nuclear waste

The high-throughput, plasma-based, mass separation techniques of nuclear waste are still an active research topic due to the theoretical and practical complexity of processing such waste. The nuclear waste can be separated according to its masses by plasma centrifugation technique. Because of this, the present research has been performed by setting up E → × B → rotation in cold cylindrical plasma surrounded by an ideally conducting homogenous shell inside a plasma centrifuge device. The results obtained are useful in analyzing the magneto-rotational instability (MRI) and trajectories of the plasma particles which are beneficial for improving the throughput and separation factor of the device.

Formation of cylindrical plasma equilibria with β > 1

Formation of cylindrical plasma equilibria with β > 1

Characterization of a radially emitting spray jet in a cylindrical inertial electrostatic confinement plasma source based on particle in cell simulation

This paper investigates the outflow mechanism of a cylindrical inertial electrostatic confinement plasma source using Particle in Cell plasma simulations. Various phenomena such as ion-wall interactions, impact ionization, excitation, and secondary electron generation are considered. Together with a fine time and cell resolution to reveal relevant phenomena. The results indicate a high electron and ion density in front of the cathode at the widest grid opening, which suggests the formation of a cascade-like charge carrier emission, commonly referred to as the “spray jet”. Initially, a virtual anode is formed within the cathode grid and is shifted toward the grid opening as time elapsed. Ions are accelerated in the plasma sheath around the cathode and collide with the cathode grids or oscillate through the grid opening. Electrons are accelerated and ionize the background gas at the plasma sheath edge. While the electron flow is disordered within the cathode it forms a cascade-like quasi-neutral plasma at the outlet of the plasma source. Through the formation of a virtual anode the discharge becomes self-sustained. With this simulation results the working principle of the inertial electrostatic confinement plasma source can be derived.

A diagnostic method of radial electron density distribution based on microwave transmission of cylindrical plasma along multipath

Based on the multipath propagation phase shift of electromagnetic wave in cylindrical plasma, a method to obtain the radial electron density distribution of non-uniform cylindrical plasma is proposed in this paper. Focused lens antennas are used in multipath transmission distribution diagnosis (MTDD), where the propagation area in the plasma is approximately the size of the focal spot. The equivalent propagation thickness at each layer can be calculated for each path based on the propagation region and layer thickness. Combining with Fermat's shortest wavelength principle, electromagnetic waves propagate in a straight line between different layers. The phase shift caused by the propagation of electromagnetic waves in each layer, starting from the outermost layer, can obtain layer by layer electron density. To validate the MTDD method, multipath transmission propagation phase shift was simulated in CST, and the electron density distribution was obtained, which has a good agreement with the preset electron density. In addition, the MTDD method was applied to inductively coupled plasma, and the diagnostic results showed high agreement with the Langmuir probe results. The proposed MTDD method has higher spatial resolution than the transmission diagnosis method and can provide more precise plasma parameter information.

Isochronous bifurcations of magnetic islands in tokamaks

On a rational magnetic surface, an isochronous bifurcation transforms one island chain into another chain with the same winding number. This transformation has been the subject of recent studies in tokamak plasmas. Namely, visco-resistive magnetohydrodynamic simulations of NSTX-U and DIII-D plasmas showed the onset of bifurcations with new magnetic isochronous islands for two competing helical perturbations on the same rational magnetic surface. To investigate these bifurcations, we use a cylindrical plasma model, with first-order correction for toroidicity, subject to externally applied magnetic perturbations, generated by a pair of resonant helical windings (RHWs) on the external wall and superposed to a helical current sheet (HCS) located on a rational plasma surface. We numerically integrate the magnetic field line equation and show that isochronous islands emerge when the perturbation created by the HCS increases. We present examples of such bifurcations on primary and secondary magnetic surfaces for different RHW configurations.

Direct laser acceleration: A model for the electron injection from the walls of a cylindrical guiding structure.

We use analytical methods and particle-in-cell simulation to investigate the origin of electrons accelerated by the process of direct laser acceleration driven by high-power laser pulses in preformed narrow cylindrical plasma channels. The simulation shows that the majority of accelerated electrons are originally located along the interface between the channel wall and the channel interior. The analytical model based on the electron hydrodynamics illustrates the underlying physical mechanism of the release of electrons from the channel wall when irradiated by an intense laser, the subsequent electron dynamics, and the corresponding evolution of the channel density profile. The quantitative predictions of the total charge of released electrons and the average electron density inside the channel are validated by comparison with the simulation results.

Identification of nonlinear effects of background asymmetry on solitary oscillations in a cylindrical plasma

A symmetry-breaking in rotational spatial pattern of quasi-periodic solitary oscillations is revealed with tomography measurement of plasma emission, simultaneously with background asymmetry in stationary plasma structure. Although the oscillatory pattern deformation is a natural course in the presence of asymmetry, elaborate analyses identify existence unfeatured nonlinear effects of the background asymmetry, i.e., its nonlinear couplings with harmonic modes of rotational symmetry, to produce non-harmonic mode to break the symmetry and cause the oscillatory pattern to be chaotic. The findings suggest the unrecognized fundamental process for plasmas to be turbulent.

Experimental demonstration of radius-varying active plasma lensing for laser-plasma-accelerated proton beams with increased collection angle

Active plasma lensing, a compact method for intensifying the focus of charged particle beams by providing a magnetic field gradient of kT/m, has emerged as a sought-after technology in laser plasma accelerator applications. However, the utilization of active plasma lenses faces significant hurdles when dealing with laser-driven proton pulses, characterized by their broad bandwidth and high divergence. To address this challenge, we developed a novel active plasma lens with a variable radius, specifically designed to optimize lens geometry in accordance with the beam envelope, and performed the first measurement of its focusing ability. The experimental findings reveal that, compared to conventional cylindrical active plasma lenses, our radius-varying lens exhibits a 2.0-fold improvement in single-energy transmission efficiency, while maintaining comparable achromatic ability. This breakthrough is anticipated to significantly contribute to the miniaturization of laser proton accelerators. Published by the American Physical Society 2024

Prototype of a 2.45 GHz cylindrical ceramic dielectric antenna surface wave plasma source for flood gun

In modern ion implanters, plasma flood gun (PFG) is used to neutralize wafer charge during doping process, preventing the breakdown damage of floating wafers caused by the space charge accumulation. Surface wave (SW) plasma source is a potential choice for PFG, because of its no metal pollution, simple structure, high current intensity and low cost for ion implanters. At Peking University (PKU), a 2.45 GHz surface wave PFG (SW-PFG) with a cylindrical dielectric antenna was designed and tested recently. It aims to obtain plasma at the gas pressure of several 10−3 Pa and below which is strictly required by the ion implanter. A two-dimensional discharge model was established to optimize the cylindrical dielectric antenna structure. Through optimization of operation parameters, the electron current intensity of 88 mA was obtained with RF power 500 W and gas pressure 5.0 × 10−3 Pa in the experiments, which meets the requirement of ion implanters. Further, through optimization of operation parameters, the electron current intensity could reach 140 mA. In addition, by setting the graphite liner to isolate the metal cavity wall and plasma, the improvement in the long-term operation stability has been confirmed, which laid a solid foundation for the industrial application of the SW-PFG.

Dust magnetoacoustic waves in an inhomogeneous cylindrical four-component dusty plasma in the presence of polarization force

Abstract Dust magnetoacoustic waves have been examined in an inhomogeneous, bounded, cylindrical dusty plasma containing oppositely polarized dust particles. Considering polarization force, dust dynamics in r − θ plane is studied in the presence of inhomogeneous external magnetic field along z axis. At equilibrium, the dusty plasma components are supposed to follow Gaussian density distribution. Using reductive perturbation method (RPM), a variable coefficient cylindrical Kadomtsev–Petviashvili (VCCKP) equation has been derived. For weak azimuthal perturbation, an analytical solution, obtained by Zhang (“Exact solutions of a kdv equation with variable coefficients via exp-function method,” Nonlinear Dynam., vol. 52, nos. 1–2, pp. 11–17, 2008) using Exp-function method, is chosen. Phase velocity of dust magnetoacoustic wave is found to be modified by the density inhomogeneities, polarization force, dust charge state ratio and ion-to-electron temperature ratio. Spatio-temporal evolution of the dust number densities has been noticed. Existence of the compressive electromagnetic solitary waves is observed numerically for the chosen dusty plasma parameter range. The impacts of the inhomogeneity, polarization force, dust charge state ratio and ion-to-electron temperature ratio on the relative amplitude of the dust magnetoacoustic wave are also discussed.

Shear Alfvén waves within magnetic islands

We calculate Alfvén eigenmodes within a magnetic island (MiAE) which have been conjectured over a decade ago. Starting from a cylindrical plasma equilibrium, we calculate the complete metric of the island interior assuming an iota profile with a constant shear for Wendelstein 7-X parameters. Then, we solve the resulting Magneto-Hydrodynamic equations inside the island optionally considering Finite Larmor Radius corrections. We find various eigenmodes in the lowest gaps for n = 0. The eigenmode with the lowest frequency shows a weakly non-linear dependence on the island width which deviates considerably from an earlier estimate.

Inward particle transport driven by biased endplate in a cylindrical magnetized plasma

The inward particle transport is associated with the formation of peaked density profiles, which contributes to improve the fusion rate and the realization of steady-state discharge. The active control of inward particle transport is considered as one of the most critical issues of magnetic confinement fusion. Recently, it is realized preliminarily by adding a biased endplate in the Peking University Plasma Test (PPT) device. The results reveal that the inward particle flux increases with the bias voltage of the endplate. It is also found that the profile of radial electric field ( ) shear is flattened by the increased bias voltage. Radial velocity fluctuations affect the inward particle more than density fluctuations, and the frequency of the dominant mode driving inward particle flux increases with the biased voltage applied to the endplate. The experimental results in the PPT device provide a method to actively control the inward particle flux using a biased endplate and enrich the understanding of the relationship between shear and turbulence transport.

Development of a planar ICP ion source for fusion based neutron generator

In this paper preliminary results of a new planar ICP ion source for neutron generator is investigated. This ion source has a cylindrical planar Aluminum plasma chamber. Set of Niobium permanent magnets have been arranged as multicusp geometry around the chamber to improve the plasma density and reduce the operational pressure. A copper made helical antenna has been used which is connected to the 2 kW 13.56 MHz radiofrequency power source including matching network. Preliminary results of ion beam measurements using 1 and 3 mm diameter apertures on plasma electrodes, represents improvement of ion current from μA range to mA with Helium operational gas. A primary result with Deuterium gas indicates that the ion current improves up to 7 mA by applying multicusp magnetic field around the plasma chamber at similar operational parameters with 1 kW of RF power. Theoretical and experiments are performed to regulate the optimum distance between plasma and the accelerating electrodes to have parallel deuteron ion beam at around 65 kV electrical potential between them. Accelerating electrode configuration which suppresses the secondary electron generated on the target surface is designed and fabricated based on the simulation results.

High-frequency dissipative MHD waves in straight magnetic cylindrical plasma: Coronal loops heating application

The theoretical model for analyzing the waves and oscillatory behavior in the structured solar corona using straight magnetic cylindrical geometry filled with uniform low-β plasma has been recognized as the most preferable classical model for the last few decades. A number of observations, since the first observation of the transition region and coronal explorer to the latest ones, have been adequately explained by adopting this model. In order to analytically formulate the oscillatory characteristics of magnetohydrodynamic (MHD) waves, most of the studies have considered the nature of plasma as an ideal fluid, particularly in the context of solar physics. However, a departure from ideal plasma consideration to non-ideal may lead to a number of modifications in the characteristics of the MHD waves, including its damping too. In what follows, we derive a more general analytical dispersion relation by extending the classical dispersion relation of [Edwin and Roberts, “Wave propagation in a magnetic cylinder,” Sol. Phys. 88, 179–191 (1983)] taking into account the effect of plasma viscosity as a non-ideal term in the existing formulations of the classical model. Consequently, the effects of viscosity on the damping of sausage and kink modes are examined in detail. Multiple trapped body waves of different frequencies exist for both kink and sausage modes in which trapped sausage body wave of comparatively high frequency is damped potentially to generate enough energy to balance the radiative losses of the coronal loop regions. For the coronal loop's plasma parameters, it is found that trapped first radial overtone body wave of sausage type is able to balance the radiative losses of coronal loop structure provided magnetic field strength does not exceed its value of more than 20G.

Spatial Distribution Analyses of Axially Long Plasmas under a Multi-Cusp Magnetic Field Using a Kinetic Particle Simulation Code KEIO-MARC

To realize the development of a long plasma source with a uniform electron density distribution in the axial direction, the spatial distribution of plasma under a multi-cusp magnetic field was analyzed using a KEIO-MARC code. Considering a cylindrical plasma source with an axial length of 3000 mm and a cross-sectional diameter of 100 mm, in which the filament electrode was the electron source, the electron density distribution was calculated using the residual magnetic flux density, Bres, and the number of permanent magnets installed at different locations surrounding the device, Nmag, as design parameters. The results show that both Bres and Nmag improved the uniformity of the electron density distribution in the axial direction. The maximum axial electron density decreased with increasing Nmag and increased with increasing Bres. These trends can be explained by considering the nature of the multi-cusp field, where particles are mainly confined to the field-free region (FFR) near the center of the plasma column, and the loss of particles due to radial particle transport. The use of multiple filaments at intervals shorter than the plasma decay length dramatically improved axial uniformity. To further improve axial uniformity, the filament length and FFR must be properly set so that electrons are emitted inside the FFR.

Impact of strong magnetization in cylindrical plasma implosions with applied B-field measured via x-ray emission spectroscopy

Impact of strong magnetization in cylindrical plasma implosions with applied B-field measured via x-ray emission spectroscopy

Plasma density distribution and its perturbation by probes in axially symmetrical plasma

An analysis of plasma density distributions at arbitrary ion–atom collisionality for one-dimensional axially symmetrical cylindrical and annular plasmas is presented. Perturbations of plasma densities caused by a cylindrical probe are studied for arbitrary ion–atom collisionality. Analytical expressions for the plasma characteristics near the probe for low collisionality have been obtained. The plasma was modeled by the hydrodynamic neutral plasma equations, taking into account ionization, ion inertia, and a non-linear ion frictional force, which dominates the plasma transport at low gas pressures. Significant plasma density depletion around the probe has been observed for a wide range of ion–atom collisionality. The presented results predict underestimation of plasma density obtained from the classical Langmuir probe procedure and should provide a better understanding of electrostatic, magnetic, and microwave probes inserted into plasmas at low gas pressure.