Plasma Excitation Research Articles

Effects of duty ratio on liquid- and polymer-surface treatment by a unipolar microsecond-pulsed helium atmospheric-pressure plasma jet

Effects of duty ratio of a unipolar microsecond-pulsed helium atmospheric-pressure plasma jet (APPJ) on liquid- and polymer-surface treatments were investigated. In addition, changes in the plasma plume length, gas temperature, excitation temperature, discharge current, absorption power, and optical emission spectra were examined by varying the other operating parameters, such as applied voltage and additive flow of oxygen or water vapor. As an example of liquid sample, de-ionized water (DW) was exposed to an APPJ, and the concentrations of the reactive species generated in the DW were measured as functions of the operating parameters. Polycarbonate, polypropylene, and polymethylmethacrylate were employed as exemplary substrate materials to investigate the effect of plasma treatment on polymeric surfaces. The APPJ treatment increased the surface energy and changed the wetting characteristics of the surface from hydrophobic to hydrophilic. X-ray photoelectron spectroscopy results showed that a short-time plasma treatment with He and/or He/O2, He/H2O affects the surface wettability owing to the introduction of polar groups.

P‐1.4: Oxygen‐Plasma Induced Generation of Mobile Charge Carriers in Indium‐Tin‐Zinc Oxide

Mobile charge carriers can be generated in indium‐tinzinc oxide (ITZO) covered with a silicon oxide layer when subjected to an oxygen plasma treatment. The resulting ‍resistivity is sensitive to the thickness of the cover oxide, the plasma excitation power, and the treatment time. With 280 ‍nm of cover oxide and 10 mins of treatment, a low resistivity of 1.2 mΩ∙cm can be obtained in a plasma biased ‍with a radio frequency excitation power of 100 W and an inductively coupled plasma excitation power of 2000 W. ‍The treatment has been deployed to form the source/drain regions of a self‐aligned, top‐gate ITZO thin‐film ‍transistor.

Design and Fabrication of Birdcage Resonators for Low-pressure Plasma Excitation

Design and Fabrication of Birdcage Resonators for Low-pressure Plasma Excitation

Spatio-temporal variation of Laguerre–Gaussian laser pulse and its effect on electron acceleration

In this paper, the longitudinal and transverse variation of Laguerre Gaussian laser pulse has been investigated, when it is propagating inside the nonlinear plasma medium under the united impact of both relativistic and ponderomotive nonlinearity. Two second-order differential equations for transverse and longitudinal pulse width parameters have been derived using the approach of method of moments. The solution of both equations are obtained numerically and variation in spatio-temporal pulse width parameters is obtained. The excited plasma wave generated by the laser-plasma interaction, accelerate the plasma electrons to high gradients. The effect of the spatio-temporal variation on electron acceleration has also been studied and it has been observed that the laser pulse with smaller pulse duration results in better energy gain by the electrons.

Topological Langmuir-cyclotron wave.

A theory is developed to describe the topological Langmuir-cyclotron wave (TLCW), a topological excitation in magnetized plasmas recently identified by numerical simulations. As a topological wave in a continuous medium, the TLCW propagates unidirectionally without scattering in complex boundaries and can be explored as an effective mechanism to energize particles. We show that, because momentum space in continuous media is contractible in general, the topology of the wave bundles is trivial over momentum space that contains no degeneracy points. This is in stark contrast to condensed matters with periodic lattice structures that impose nontrivial topology on momentum space. In continuous media without lattice structures, nontrivial topology of the eigenmode bundles manifests over phase space, and it is the nontrivial topology over phase space that underpins the topological excitations, such as the TLCW. It is shown that the TLCW can be faithfully modeled by a generic tilted Dirac cone in phase space, whose entire spectrum, including the spectral flow, is given.

Comparison of excitation and kinetic temperatures in a laser-produced plasma using absorption spectroscopy.

High-resolution tunable laser absorption spectroscopy is used to measure time-resolved absorption spectra for six neutral uranium transitions in a laser-produced plasma. Analysis of the spectra shows that kinetic temperatures are similar for all six transitions, but excitation temperatures are higher than kinetic temperatures from 10-100 μs, indicating departures from local thermodynamic equilibrium.

Factors affecting decolourization efficiency of indigo carmine in a coaxial surface plasma falling film reactor

Low temperature plasmas generated in close proximity to water offers a convenient means of generating highly oxidising aqueous phase chemical species capable of degrading recalcitrant organic compounds. To ensure the efficacy of the approach the interplay between the plasma excitation parameters and reactor characteristics must be optimised to facilitate efficient generation and transport of reactive chemical species from the plasma phase to the liquid. In this study, indigo carmine dye was used as a model contaminant to investigate factors affecting degradation efficacy in a coaxial falling film reactor coupled to a surface barrier discharge. Plasma generated species in the gas phase were characterised using Fourier transform infra-red spectroscopy and linked to aqueous phase species in the exposed solution. Parameters including dissipated power, pulse width modulation and reactor sealing conditions were systematically investigated to reveal a maximum decolourisation efficiency of 20.18 g/kWh. Through a comparison with other plasma-based and non-plasma-based advanced oxidation processes it was revealed that the coaxial surface barrier falling film reactor developed in this study is highly competitive and worthy of further investigation.

Coexistence of Compressive and Rarefactive Positron-Acoustic Electrostatic Excitations in Unmagnetized Plasma with Kaniadakis Distributed Electrons and Hot Positrons

Coexistence of Compressive and Rarefactive Positron-Acoustic Electrostatic Excitations in Unmagnetized Plasma with Kaniadakis Distributed Electrons and Hot Positrons

Control system of high-voltage pulse power supply for compact torus injector based on EPICS

The Compact Torus Injector (CTI) is a magnetic confinement fusion device feeding system, which injects the excited compact toroidal plasma into the target device at high speed, and controls the fuel injection and injection speed to achieve optimal control of the density pressure profile of the magnetic confinement fusion device. As the important subsystem of the CTI, the CTI High-Voltage Pulse Power Supply (HVPPS) system consists of five sets of power supply. This paper uses EPCIS as a development platform to design the control system of the CTI HVPPS which realizes timing sequential control, status detection, parameter setting and read-back status of the CTI power supplies with different communication interfaces and protocols. The discharge experiments are performed on the CTI. The experimental results prove that the control system meets the real-time control requirements of CTI devices for HVPPS. (Abstract)

Overcoming the matrix effect in the element analysis of steel: Laser ablation-spark discharge-optical emission spectroscopy (LA-SD-OES) and Laser-induced breakdown spectroscopy (LIBS)

The optical emission of plasma on industrial steel samples induced by Laser Ablation-Spark Discharge-Optical Emission Spectroscopy (LA-SD-OES) and by Laser-Induced Breakdown Spectroscopy (LIBS) is investigated and correlated to the volume of ablated steel material. The 36 steel samples investigated have an iron content C(Fe) above 94 wt%. The excitation energy in LIBS (laser pulse of 55 mJ) and in LA-SD-OES (laser pulse of 5 mJ and spark discharge of 50 mJ) is the same. In LA-SD-OES, the optical emission of plasma and the size of ablation craters are very similar for all samples and a linear calibration curve for Mn is measured (R2 = 0.99). In LIBS, however, a pronounced dependence of the plasma emission and of the crater volume on the steel matrix is observed and calibration curves show a strong cross-sensitivity to other elements such as Si (matrix effect). The hardness, grain size, and phase of steel samples are analyzed to correlate the matrix effect in LIBS measurements to a physical property of the specimen. The different behavior for LA-SD-OES and LIBS is probably due to different processes of sampling and plasma excitation. From our results we conclude that LA-SD-OES enables for the element analysis of industrial steel largely independent of composition and structure of samples while in LIBS the matrix effect has to be taken into account.

Comparative Analysis of Flame Propagation and Flammability Limits of CH4/H2/Air Mixture with or without Nanosecond Plasma Discharges

This study investigates the kinetic modeling of CH4/H2/Air mixture with nanosecond pulse discharge (NSPD) by varying H2/CH4 ratios from 0 to 20% at ambient pressure and temperature. A validated version of the plasma and chemical kinetic mechanisms was used. Two numerical tools, ZDPlasKin and CHEMKIN, were combined to analyze the thermal and kinetic effects of NSPD on flame speed enhancement. The addition of H2 and plasma excitation increased flame speed. The highest improvement (35%) was seen with 20% H2 and 1.2 mJ plasma energy input at ϕ = 1. Without plasma discharge, a 20% H2 blend only improved flame speed by 14% compared to 100% CH4. The study found that lean conditions at low flame temperature resulted in significant improvement in flame speed. With 20% H2 and NSPD, flame speed reached 37 cm/s at flame temperature of 2040 K at ϕ = 0.8. Similar results were observed with 0% and 5% H2 and a flame temperature of 2200 K at ϕ = 1. Lowering the flame temperature reduced NOx emissions. Combining 20% H2 and NSPD also increased the flammability limit to ϕ = 0.35 at a flame temperature of 1350 K, allowing for self-sustained combustion even at low temperatures.

Atomic layer deposition of α-Al2O3 from trimethylaluminum and H2O: Effect of process parameters and plasma excitation on structure development

Aluminum oxide (Al2O3) thin films were deposited from trimethylaluminum (TMA) and H2O on Si substrates and α-Cr2O3 seed layers using thermal and plasma-assisted atomic layer deposition (ALD). All films deposited on Si were amorphous. On the α-Cr2O3 seed layers, α-Al2O3 was formed at temperatures ≥350 °C in the thermal ALD and at ≥325 °C in the plasma-assisted ALD processes. The Ar plasma used in the experiments most significantly contributed to crystallization when applied during the purge period following the H2O pulse or during the H2O pulse and the following purge. Application of plasma during the TMA pulse, during the purge following the TMA pulse, or only during the H2O pulse suppressed the crystal growth and could potentially be applied as a crystal growth inhibitor.

A high‐voltage solid‐state Marx generator with adjustable pulse edges

AbstractMost reactors for non‐thermal plasma excitation are capacitive to pulse generators. The density and temperature of electrons in plasma are dominated by the discharging currents which are proportional to the pulse edges. However, adjusting the pulse edges is quite challenging since the switching speed and the inductance and capacitance in the discharging loops dominate them. This study proposes a drive circuit for solid‐state Marx generators with adjustable edges. The drive circuit controls the Miller plateau by adjusting the gate voltage amplitude to adjust both the rise time and fall time of pulses continuously and independently. The influence of the gate voltage on the Miller plateau and the rise time is studied. The feasibility is verified by both simulating and experimental results. An 8‐stage solid‐state Marx generator prototype was built, and 4.8‐kV pulses with a rise time in the range of 79 ns‐22.21 μs were obtained over capacitive loads. Adjusting pulse edges can control the current amplitudes in dielectric barrier discharge loads.

Elemental study of Devarda’s alloy using calibration free-laser induced breakdown spectroscopy (CF‒LIBS)

In the present study, we present the compositional analysis of a Devarda’s alloy using the calibration–free laser-induced breakdown spectroscopy (CF-LIBS) technique. A nanosecond pulsed Q-switched Nd:YAG laser was focused on the target-sample under investigation to ablate its surface and the measured emission spectrum was registered by using a spectrometer (LIBS2000+) having the optical spectral within a range from 200–720 nm. The analysis of the measured optical spectra confirms the presence of three major elements Aluminum (Al), Copper (Cu), and Zinc (Zn) in the target sample. The emission intensity line profiles of Zn, Cu, and Al were utilized to estimate the plasma-parameters consisting of excitation temperature, and the plasma number density. The plasma excitation temperature was investigated using the Boltzmann-plot technique, which yields the temperature for Cu and Zn as 8547 ± 5% K and 8100 ± 5%, respectively, while the electron plasma density was calculated from the Stark-broadening of individual neutral emission lines of Al, Cu, and Zn. For the quantitative analysis of the elements that exist in the target sample, a CF-LIBS technique was employed by assuming the condition of optically thin plasma as well as local thermodynamics equilibrium. Using the CF-LIBS technique, the relative composition in the form of weight percentage was estimated to be Zn: 57%, Al: 39%, and Cu: 4%, whereas, the certified concentration of Devarda’s alloy was 50% for Zn, 45% for Al, and 5% for Cu. These measured results reveal that the elemental concentration utilizing CF-LIBS shows a reasonable agreement with standard estimates illustrated by the manufacturer. This study further suggests that the CF-LIBS technique opens up an opportunity for engineering and industrial usage of LIBS where a quantifiable study of the substance is exceedingly advantageous.

Progress towards a 3D Monte Carlo radiative transfer code for outflow wind modelling

Context. Radiative transfer modelling of expanding stellar envelopes is an important task in their analysis. To account for inhomogeneities and deviations from spherical symmetry, it is necessary to develop a 3 D approach to radiative transfer modelling. Aims. We present a 3 D Monte Carlo code for radiative transfer modelling, which is aimed to calculate the plasma ionisation and excitation state with the statistical equilibrium equations, moreover, to implement photon-matter coupling. As a first step, we present our Monte Carlo radiation transfer routines developed and tested from scratch. Methods. The background model atmosphere (the temperature, density, and velocity structure) can use an arbitrary grid referred to as the modGrid. The radiative transfer was solved using the Monte Carlo method in a Cartesian grid, referred to as the propGrid. This Cartesian grid was created based on the structure of the modGrid; correspondence between these two grids was set at the beginning of the calculations and then kept fixed. The propGrid can be either regular or adaptive; two modes of adaptive grids were tested. The accuracy and calculation speed for different propGrids was analysed. Photon interaction with matter was handled using the Lucy’s macroatom approach. Test calculations using our code were compared with the results obtained by a different Monte Carlo radiative transfer code. Results. Our method and the related code for the 3 D radiative transfer using the Monte Carlo and macroatom methods offer an accurate and reliable solution for the radiative transfer problem, and are especially promising for the inclusion and treatment of 3 D inhomogeneities.

Aeroacoustic control mechanism on near-wall-wing of Aero-train based on plasma jet

In this study, an aeroacoustic control mechanism of a plasma jet acting on a high-speed moving wing under a wing-in-ground effect is investigated. Moreover, a novel method is proposed to reduce the aeroacoustics of Aero-train wings. Numerical simulations of the aeroacoustics generated by flow around a National Advisory Committee for Aeronautics 4412 wing are performed under three different plasma excitation modes at four clearances with an incoming flow velocity of 0.3 Ma and an angle of attack of 5°. The results show that different plasma excitation modes interfere with the vortex generation and development in different ways to achieve aeroacoustic reduction. The UP excitation mode delays the airflow separation, delays the vortex generation and development, and reduces the vortex intensity. The BOTH excitation mode forces transverse vortices to transform into streamwise hairpin vortices and reduces the local pressure fluctuation intensity. Hence, plasma jets exhibit a good control effect on the peak aeroacoustics under different clearance conditions but result in the frequency shift effect of acoustic energy transfer to high frequencies. The modal analysis of the flow field of the three excitation conditions via a proper orthogonal decomposition method reveals that the trend of the modal change is similar for the three excitation conditions, and the change in each order of the modal corresponds to the energy decrease at the peak frequency and the energy increase at high frequencies.

NIR‐triggered Synergetic Photothermal and Chemotherapy Cancer Treatment Based on SiO2@Au@SiO2@QDs‐DOX Composite Structural Particles

AbstractThis paper reports the synthesis of multi‐layer SiO2@Au@SiO2@QDs nanoparticles with a dual‐functionality of simultaneous heating and temperature sensing and their applications to in vitro chemo‐thermal therapy. The heating is activated by a NIR‐light through resonance excitation of surface plasma while in‐situ thermal sensing is accomplished by the QDs photoluminescent (PL) effect. These dual function nanoparticles are used as a drug carrier for in vitro chemotherapy‐photothermal co‐treatment for malignant cells. A comparative study of drug release profiles was performed with and without 808 nm laser irradiation. The drug release rate was accelerated by a rise of temperature, which is induced by plasmonic heat generation associated with Au nanoshells; while the temperature change is monitored by the QD nanoparticles at the same time. The results showed that SiO2@Au@SiO2@QDs‐DOX platform enabled the combination of local specific chemotherapy with external near‐infrared (NIR) photothermal therapy and significantly improved the efficacy of cancer treatment. This combined treatment demonstrated synergistic chemotherapeutic‐thermal effects compared to chemotherapy or photothermal therapy alone, resulting in higher efficacy.

Simulation of hollow-cathode-nitriding plasma and design of diffusion equipment with DC and RF dual discharge

The formation and diffusion of plasma are complex and critical processes in plasma nitriding. A stable and high-concentration plasma atmosphere can effectively increase the diffusion rate and the thickness of the diffusion layer. In this study, a two-dimensional multi-physics model integrating physical kinetics, energy transfer, mass transfer, and electromagnetic induction was developed. The effect of a hollow-cathode structure on plasma distribution was investigated, and the edge effect observed on nitrided metals was eliminated. The impacts of the essential plasma diffusion parameters were simulated using the developed model. A simple but effective experiment was designed to validate the model. A diffusion furnace with DC and RF dual discharge was designed by adding a high-frequency coil to existing equipment. Subsequently, the effects of the two plasma excitation sources on the overall distribution of plasma were analyzed. Notably, the proposed model is a high-fidelity one based on actual device dimensions; therefore, it can be used to simulate, predict, and control the plasma formation process in the diffusion furnace. In addition, the model can provide reference data and guidance for optimizing the diffusion process and structural design of diffusion furnaces.

Effect of laser pulse duration on relative hardness estimation using LIBS

As the demand for a quick and remote way of hardness estimation increases, the attention to use LIBS for such application increases. Most of the studies of hardness estimation that have been done used nanosecond laser sources for LIBS while using femtosecond laser has not been studied yet. In this work, a group of five samples with different hardness were analyzed using nanosecond and femtosecond LIBS for relative hardness estimation. Almost the same wavelength was used to decrease the effect of wavelength as much as possible. Considering that the laser produced plasma is in a state of local thermodynamic equilibrium (LTE), the Boltzmann plot method was adopted to calculate the plasma excitation temperature (Te) which is closely correlated to the samples’ hardness. It was found that in case of nanosecond LIBS as the sample hardness increases the excitation temperature Te increases, while for the femtosecond LIBS the behavior was opposite and Te was found to be decreasing as the hardness of the target increases. This result may be attributed to the different plasma plume creation processes and its expansion for both nano- and femto- second lasers.

Investigation of heat and mass transfer of flow structures generated by a pulsed surface arc discharge actuator in quiescent air

Pulsed Surface Arc Discharge (PSAD) actuators can improve the aerodynamic performance of aircraft due to their fast response speed and wide frequency band. Understanding the flow structure induced by arc discharge and its transfer process is the key to the sensible use of plasma excitation for flow control. This paper has investigated the dynamic heat and mass transfer process of charged particle clusters generated by arc discharge theoretically and experimentally. The results show that the clusters are composed of charged particles, and the thermal effect is the macroscopic manifestation of the thermal motion of charged particles. The heat and mass transfer processes of charged particle clusters can be expressed as a function of temperature. During heat and mass transfer, the transfer mode of the plasma cluster composed of charged particles will change. The plasma cluster will change from forced convection in the initial stage to natural convection in the final stage, and the Richardson number is different in different stages. The heat released by the gas discharge and the heat released by the plasma mass transfer will form accumulated heat in the space and change the temperature difference, thereby affecting the process of heat and mass transfer. This paper has constructed a model describing pulsed plasma clusters' dynamic heat and mass transfer. Furthermore, the dynamic mode decomposition results of the theoretical model function show that plasma clusters mainly conduct the mass transfer through low-frequency and heat transfer through high-frequency modes.