Uniform Plasma Research Articles

Light-to-Plasma Momentum Transfer

The momentum of light in a plasma and the momentum transfer from light to plasma is calculated for a uniform plane of light incident into a uniform plasma. At low irradiance, the Minkowski and Abraham expressions for photon momentum are shown to be equivalent. We evaluate relativistic electron motion at a high irradiance for a plasma and show that most light momentum is transferred to the electrons associated with motion parallel to the light propagation at an irradiance corresponding to the reduced vector potential ao≈3.7 (reduced irradiance Iλ2≈2×1019 W cm−2 μm2). Our results show that to ensure the maximum momentum transfer from photons to electrons in motion parallel to the k-direction for fixed laser pulse energy, the laser focusing should be adjusted to achieve ao≈3.7, even if tighter focusing, and thus higher ao values, are possible.

Effect of focus ring with external circuit on cathode edge sheath dynamics in a capacitively coupled plasma

Capacitively coupled plasmas are widely used in semiconductor processes. The control of plasma to obtain uniform deposition and etching is an open problem, particularly within a few millimeters of the substrate edge. Complex material stacks commonly referred to as focus rings are placed at the wafer edge to provide uniform processes across the entire substrate but have limitations with regard to process window and eventual material erosion. One approach is to combine a focus ring with a tunable external circuit ground path termination to extend the plasma uniformity to the wafer edge over a wider process space. The external circuit coupling focus ring to the ground influences the ion energy profile and the ion angular profile by changing the impedance between the focus ring and the ground and allows wafer edge tuning over a wide range of operating parameters. In this work, it is found that the adjustable external circuit can control the partitioning of bias and RF voltages between the RF powered and passively coupled plasma facing surfaces. The focus ring with an external circuit assembly can also control the spatial distribution of plasma density and, therefore, improve the sheath edge profile. These results point to possible source designs for engineering the distribution of power dissipation and the electric field of the wafer edge in industrial plasma reactors.

Improvement on Plasma Intensity Uniformity in Rectangular DC Magnetron Sputter by Optimizing Structures of Substrate Electrode

DC magnetron sputtering is widely used for thin film deposition in the field of displays. By adding magnet arrays to a large rectangular magnetron sputtering system, while the ionization and deposition rate are increased, the film properties can be nonuniform, and the local target erosion rate can be increased. Film properties strongly depend on uniform plasma density and energy. Although the ferromagnetic shield has been used to decrease the magnetic field locally, the plasma remains nonuniform at the corners of the rectangular shape target. In this study, a plasma simulation was conducted to analyze the plasma distribution in a DC magnetron sputtering system. The plasma uniformity was improved by optimizing the thickness and shape of the substrate electrode, carefully controlling the distance between the target and substrate electrode based on Paschen’s law, leading to the reduction of local high plasma intensity.

Effects of a radial variation of surface coefficients on plasma uniformity in capacitive RF discharges

With the increasing demands toward large area plasma etching and deposition, the radial uniformity of capacitively coupled plasmas (CCPs) becomes one of the key factors that determine process performance in industrial applications. However, there is a variety of parasitic effects, e.g. electromagnetic and electrostatic edge effects, that typically lead to the formation of nonuniform radial plasma density profiles at various discharge conditions with a density peak appearing either at the center or near the edges of the electrodes. Moreover, in commercial CCPs different surface materials are in contact with the plasma at various positions as parts of boundary surfaces such as focus rings, masks, showerhead electrodes, wall and/or target materials. Via complex material specific plasma-surface interactions, the presence of such different surface materials affects plasma uniformity in a way that is typically not understood and, thus, not controlled. In this work, aided by 2d3v graphics processing unit accelerated particle-in-cell/Monte Carlo collision simulations, we study the effects of radial variations of electrode materials on the plasma via their different ion and electron induced secondary electron emission as well as electron reflection coefficients on the discharge characteristics. Based on such fundamental understanding we tailor the radial variation of boundary surface materials to improve plasma uniformity in low pressure CCPs. Such investigations are performed at different neutral gas pressures, where both center and edge high radial plasma density profiles form in the presence of radially uniform surface coefficients that resemble the presence of a single electrode material. It is demonstrated that by radially varying the surface coefficients at the grounded electrode, the radial plasma density profile can be finely adjusted and the plasma uniformity above the wafer placed at the powered electrode can be improved in both cases.

Laser wakefield acceleration of electrons using Bessel–Gauss doughnut beams for accelerating beam guiding

A high-intensity laser pulse propagating through a gas target disturbs the uniform plasma distribution. Plasma density structures, created by high-order Bessel–Gauss beams for guiding the accelerating Gaussian beam and laser wakefield acceleration of electrons, are analysed using Wake-T and Fourier–Bessel particle-in-cell (FBPIC) simulation tools. The use of Bessel–Gauss doughnut beams increases the acceleration distance and energy of accelerated electrons up to 2.3 times at a 2 mm distance relative to the Gaussian beam of the same intensity.

Broadband microwave absorption effects in 2D nitrogen capacitively coupled plasma under different operating conditions

In recent years, the interaction of electromagnetic waves (EM) with plasma sources under argon and helium discharges has been extensively studied due to its potential applications in plasma stealth. However, nitrogen, as a more economical discharge gas, has been ignored in terms of its absorption of EM waves and stealth effect. In this work, a numerical calculation model combining two-dimensional capacitively coupled plasma (CCP) fluid model and EM wave model was developed to investigate the plasma uniformity degree and broadband microwave absorption effects in helium and nitrogen CCP. It is concluded that the two-dimensional model in this paper has more accurate and reasonable through comparison with the one-dimensional and experimental results in helium CCP. Nitrogen CCP shows better broadband absorption effects than that of helium, and helium plasma has better uniformity than nitrogen under the same discharge parameters. But the uniformity degree of nitrogen plasma is not much different from that of helium under the same electron density, which means that nitrogen can significantly improve its broadband wave absorption properties to some extent without loss of uniformity degree. Based on the above conclusions, the absorption characteristics of nitrogen CCP under different radio frequency (RF) power and pressure are analyzed. The attenuation effect of nitrogen CCP increases with the increasing RF power, and it is interesting that the influence of pressure on the attenuation of EM waves is not monotonically increasing, and the related mechanism is discussed. Finally, discussion of skin depth under different RF power and pressure validates the above conclusions. The absorption band of nitrogen CCP under the best parameters in this work can reach the X-band, which shows great application potential in plasma stealth.

Uniform plasma generation with filament assisted DC discharge in a linear plasma device

Uniform and quiescent (δ n/n < 0.5%) laboratory plasma has been produced in a linear plasma device with a simple filament-assisted DC source without using any magnetic field for plasma confinement. A filament-assisted DC plasma source has been designed, fabricated in-house, and operated successfully to achieve the desired plasma parameters. A stainless steel(ss)-grid is placed in-front of the filament assembly and biased appropriately using a DC-regulated power supply to accelerate thermionically emitted electrons from the heated filaments along the length of the main chamber and facilitate the production of uniform plasma. Heating of the filaments was done by passing a current of ∼3.8 − 4.2 A through it using another DC-regulated power supply. 2-dimensional spatial profiles of plasma density (n e ), electron temperature (T e ) and plasma potential (V P ) obtained from the Langmuir Probe measurements by inserting 4 number of Langmuir Probes inside the plasma from 4 co-linear radial ports of the plasma chamber and scanning them radially with the help of indigenously built probe drive setups reveal spatially uniform plasma generation with n e in the range ∼(1 − 2) × 1015 m−3 and T e ∼ (2.5 − 3.5) eV. Variations of plasma parameters and its spatial uniformity with neutral pressure are also investigated. It is observed that the spatial uniformity of the plasma produced at neutral pressures in the range of ∼(3 − 6) × 10−4 mbar is very good with δ n/n < 0.5%.

Coplanar Capillary Plasma Electrode Discharge Flat-Panel Lamps Based on Porous Anodic Alumina

A coplanar capillary plasma electrode discharge is a promising source owing to its superior performance. In this study, a coplanar capillary plasma electrode discharge flat-panel plasma lamp fabricated from porous anodic alumina and glass was designed to investigate its properties. Coplanar capillary plasma electrode discharge flat-panel lamps with porous anodic alumina dielectric layers were fabricated and investigated. Changing of the frequency and voltage of the power supply and altering of the thickness of the dielectric layers and the interval distance of the electrode were carried out to optimize the performance of the lamps by decreasing the spark-ignition voltage and enhancing the luminous efficacy. The luminance can exceed 7200 Cd/m2 and the white light flux efficacy is more than 4.92 lm/W. The discharge process of capillary plasma electrode discharge was modeled and simulated using COMSOL Multiphysics. The electron density and temperature were also analyzed. The results show that small plasma jets were produced at the pores of the porous anodic alumina, which helped stabilize the plasma. The voltage in the gas gap changes sharply with the geometry of the porous anodic alumina dielectric layer, leading to a higher electric field. The spark-ignition voltage decreased. Small plasma jets increase the plasma uniformity. The electron density and electron temperature reach approximately 1.94 × 108 m3 and 3.34 eV, respectively. A high electric field intensity produced at the porous anodic alumina validated the promising potential in related fields.

Real-time monitoring of the plasma density distribution in low-pressure plasmas using a flat-cutoff array sensor

In the industrial semiconductor plasma processing, plasma density and its spatial distribution are critical for the understanding of discharge physics and the enhancement of the processing yield via monitoring of the status of plasma processing. Thus, real-time monitoring of plasma density and uniformity in the wafer region during wafer processing have been receiving significant attention. In this study, we developed an electrode-embedded flat-cutoff array sensor for the real-time measurement of electron density uniformity during wafer processing. We measured the spatial distribution of electron density on the wafer surface, compared it with the results measured in the bulk plasma region, and found different plasma distributions between the two where this difference can be attributed to local electron kinetics. We also performed plasma etching of amorphous carbon materials, which showed a clear correlation with the electron density distribution measured by the flat-cutoff array sensor. This indicates that the electron density distribution on the wafer surface is crucial for the process result. Thus, the array sensor developed in this study can be applied not only to measure plasma uniformity but also to predict the wafer process beforehand, making it highly significant for industrial plasma processing methods, such as virtual metrology.

Time‐dependent charged particle stopping in quantum plasmas: testing the G1–G2 scheme for quasi‐one‐dimensional systems

AbstractWarm dense matter—an exotic, highly compressed state on the border between solid and plasma phases is of high current interest, in particular for compact astrophysical objects, high‐pressure laboratory systems, and inertial confinement fusion. For many applications, the interaction of quantum plasmas with energetic particles is crucial. Moreover, often the system is driven far out of equilibrium. In that case, there is high interest in time‐dependent simulations to understand the physics, in particular, during thermalization. Recently a novel many‐particle technique, the G1–G2 scheme was presented with reference to the study by Schlünzen et al. (2020) which allows for first‐principle simulations of the time evolution of interacting quantum systems. Here we apply this scheme to a spatially uniform dense quantum plasma (jellium) and explore its performance. To this end, the G1–G2 scheme is transformed into momentum representation, and first results are presented for a quasi‐one‐dimensional model system.

Particle motion and lensing with plasma of acoustic Schwarzschild black hole

This paper is motivationally based on the study revealing the characteristics of Acoustic Schwarzschild BHs in respect of particle dynamics, and weak gravitational plasma lensing. We discuss the particle dynamics by studying the effective potential, ISCO, for massive particle and photon motion. We consider the weak gravitation field to study the gravitational lensed photons. This purpose of lensing is served by taking under consideration three fields of plasma uniform plasma, singular isothermal sphere and a nonsingular isothermal sphere. Each field is separately incorporated to calculate the plasma deflection angle, which is further utilized in the image magnification associated with the source brightness for uniform plasma and singular isothermal sphere as a selective case. All the obtained results are compared with the Schwarzschild black hole case as a standard.

Plasma-Activated Mist: Continuous-Flow, Scalable Nitrogen Fixation, and Aeroponics

Nitrogen fixation underpins diverse biological and industrial processes and is currently one of the leading producers of carbon emissions at a global scale. Radical solutions to decarbonize nitrogen fixation include plasma-electrified ammonia (NH3) synthesis using water and atmospheric nitrogen. Here, we resolve the intrinsic limitations of the state-of-the-art solutions in (i) energy efficiency; (ii) scalability; (iii) direct use of clean renewable energy; and (iv) direct sustainable application of water-based nitrogen fixation by the novel, scalable plasma-enabled process and system for the continuous-flow, scalable nitrogen fixation, and aeroponics using plasma-activated mist (PAM). The new approach is based on the continuous, scalable, in-flow generation of PAM containing NH4+, NO3–, NO2–, and other nitrogen-fixation species through the reaction of large-area uniform air plasma and high-flux water mist containing large area-to-volume ratio micron-sized droplets. Through the solar-energy-driven plasma-assisted oxidation confined within the droplet micro-reactors, a liquid-phase nitrogen fixation product dominated by NO3– is produced. This PAM nitrogen fixation system is applied for the continuous delivery of nitrogen-based nutrients directly to the roots of living plants using a custom-designed aeroponic system which increases the leaf emergence rate and leaf area of bean sprouts by more than 30%. The unique energy concentration in droplet microreactors leads to the much increased (from 2 to 39 times) energy efficiency at a larger scale compared to the key types of common lab-scale plasma reactors. Compatibility with direct solar power, flow-reactor chemistry, and electrified processes at industry-relevant scales make this low-cost, low-carbon-footprint, renewable-energy-driven process and system promising for the widespread sustainable and distributed production and applications of plasma-enabled nitrogen fixation.

A Novel Design Eco-friendly Microwave-assisted Cu–N@CQDs Sensor for the Quantification of Eravacycline via Spectrofluorimetric Method; Application to Greenness Assessments, Dosage Form and Biological Samples

Community-acquired pneumonia is one of the most common infectious diseases and a substantial cause of mortality and morbidity worldwide. Therefore eravacycline (ERV) was approved by the FDA in 2018 for the treatment of acute bacterial skin infections, GIT infections, and community-acquired bacterial pneumonia caused by susceptible bacteria. Hence, a green highly sensitive, cost-effective, fast, and selective fluorimetric approach was developed for the estimation of ERV in milk, dosage form, content uniformity, and human plasma. The selective method is based on the utilization of plum juice and copper sulphate for the synthesis of green copper and nitrogen carbon dots (Cu–N@CDs) with high quantum yield. The quantum dots' fluorescence was enhanced after the addition of ERV. The calibration range was found to be in the range 1.0 – 80.0 ng mL−1 with LOQ equal to 0.14 ng mL−1 and LOD was found to be 0.05 ng mL−1. The creative method is simple to deploy in clinical labs and therapeutic drug health monitoring system. The current approach has been bioanalytically validated using US-FDA and validated ICH criteria. High-resolution transmission electron microscopy (HR-TEM), X-ray photon spectroscopy (XPS), Zeta potential measurements, fluorescence, UV–VIS, and FTIR spectroscopy have all been used to fully characterize the Cu–N@CQDs. The Cu–N@CQDs were effectively applied in human plasma and milk samples with a high percentage of recovery ranging from 97.00 to 98.80%.

Localization of electron modes in nonuniform helicon plasma

New guided electrostatic and electromagnetic modes propagating in a nonuniform magnetized plasma with plane geometry are presented. The modes may arise in a plasma with a region of strong inhomogeneity leading to a concentration of wave energy and, thus, a localization of the modes. These localized modes can only propagate if the density gradient is sufficiently strong, whereas they do not exist in weakly nonuniform plasma. The eigenfunctions and the spectrum of the modes are found. In detail, the properties of the modes are studied for particular profiles in the transitional layer between two uniform plane plasma regions.

The engineering design of half-size RF negative ion source for CRAFT-NNBI

The full-size radio frequency (RF) negative ion source used in comprehensive research facility for fusion technology (CRAFT) has four drivers, which are arranged in the vertical direction. In order to study the physical and engineering issues, a quarter-size negative ion source was designed, developed and tested in ASIPP. This source has only one driver, making it impossible to research radio frequency interference and large-area plasma uniformity when multiple drivers work together. Therefore, a half-size negative ion source with dual drivers is developed in this study. The half-size negative ion source with dual drivers has been successfully developed and used as a module. Two half-size negative ion sources were assembled after the improvement to complete the overall design of the full-size negative ion source, which is of great significance to the entire beam source project. This paper mainly introduced the structural design, structural finite element analysis and key component manufacturing process test of the half-size negative ion source.

Explicit dispersion relations for warm fluid waves in a uniform plasma (invited)

Explicit dispersion relations for warm fluid waves in a uniform plasma (invited)

Development of the Tele-Measurement of Plasma Uniformity via Surface Wave Information (TUSI) Probe for Non-Invasive In-Situ Monitoring of Electron Density Uniformity in Plasma Display Fabrication Process.

The importance of monitoring the electron density uniformity of plasma has attracted significant attention in material processing, with the goal of improving production yield. This paper presents a non-invasive microwave probe for in-situ monitoring electron density uniformity, called the Tele-measurement of plasma Uniformity via Surface wave Information (TUSI) probe. The TUSI probe consists of eight non-invasive antennae and each antenna estimates electron density above the antenna by measuring the surface wave resonance frequency in a reflection microwave frequency spectrum (S11). The estimated densities provide electron density uniformity. For demonstration, we compared it with the precise microwave probe and results revealed that the TUSI probe can monitor plasma uniformity. Furthermore, we demonstrated the operation of the TUSI probe beneath a quartz or wafer. In conclusion, the demonstration results indicated that the TUSI probe can be used as an instrument for a non-invasive in-situ method for measuring electron density uniformity.

Photon Acceleration from Optical to XUV.

The propagating density gradients of a plasma wakefield may frequency upshift a trailing witness laser pulse, a process known as "photon acceleration." In uniform plasma, the witness laser will eventually dephase because of group delay. We find phase-matching conditions for the pulse using a tailored density profile. An analytic solution for a 1D nonlinear plasma wake with an electron beam driver indicates that, even though the plasma density decreases, the frequency shift reaches no asymptotic limit, i.e., is unlimited provided the wake can be sustained. In fully self-consistent 1D particle-in-cell (PIC) simulations, more than 40 times frequency shifts were demonstrated. In quasi-3D PIC simulations, frequency shifts up to 10 times were observed, limited only by simulation resolution and nonoptimized driver evolution. The pulse energy increases in this process, by a factor of 5, and the pulse is guided and temporally compressed by group velocity dispersion, resulting in the resulting extreme ultraviolet laser pulse having near-relativistic (a_{0}∼0.4) intensity.

Weak gravitational lensing by an ESTGB black hole in the presence of a plasma

This paper is devoted to studying the weak-field gravitational lensing properties of a 4D ESTGB black hole, which is surrounded by the plasma medium. The effects of the magnetic charges and the three plasma distribution models in the deflection of light around a 4D ESTGB black hole are investigated in detail. We find that the uniform plasma leads to a larger deflection of light rays in comparison with the singular isothermal sphere (SIS), the non-singular isothermal sphere (NSIS) models. Moreover, the deflection angle increases slightly as the absolute value of the magnetic charge decreases. Finally, we analyze the total magnification of image due to weak gravitational lensing around the black hole. The result shows that the presence of a uniform plasma medium remarkably enhances the total magnification whereas the non-uniform plasma reduces the total magnification.

Ammonia decomposition in a dielectric barrier discharge plasma: Insights from experiments and kinetic modeling

Utilizing ammonia as a storage medium for hydrogen is currently receiving increased attention. A possible method to retrieve the hydrogen is by plasma-catalytic decomposition. In this work, we combined an experimental study, using a dielectric barrier discharge plasma reactor, with a plasma kinetic model, to get insights into the decomposition mechanism. The experimental results revealed a similar effect on the ammonia conversion when changing the flow rate and power, where increasing the specific energy input (higher power or lower flow rate) gave an increased conversion. A conversion as high as 82 % was achieved at a specific energy input of 18 kJ/Nl. Furthermore, when changing the discharge volume from 31 to 10 cm3, a change in the plasma distribution factor from 0.2 to 0.1 was needed in the model to best describe the conversions of the experiments. This means that a smaller plasma volume caused a higher transfer of energy through micro-discharges (non-uniform plasma), which was found to promote the decomposition of ammonia. These results indicate that it is the collisions between NH3 and the high-energy electrons that initiate the decomposition. Moreover, the rate of ammonia destruction was found by the model to be in the order of 1022 molecules/(cm3 s) during the micro-discharges, which is 5 to 6 orders of magnitude higher than in the afterglows. A considerable re-formation of ammonia was found to take place in the afterglows, limiting the overall conversion. In addition, the model revealed that implementation of packing material in the plasma introduced high concentrations of surface-bound hydrogen atoms, which introduced an additional ammonia re-formation pathway through an Eley-Rideal reaction with gas phase NH2. Furthermore, a more uniform plasma is predicted in the presence of MgAl2O4, which leads to a lower average electron energy during micro-discharges and a lower conversion (37 %) at a comparable residence time for the plasma alone (51 %).