Diagnostics and active species formation in an atmospheric pressure helium sterilization plasma source (original) (raw)
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Helium (He) and Argon (Ar) atmospheric pressure plasma jets operated with low-frequency power source are designed and studied. The current and voltage waveforms, formation of plasma jets, estimated rotational and vibrational temperatures, optical emission spectra, and numerical simulations for He and Ar gases are investigated to analyze the plasma characteristics. Ar plasma shows higher discharge current and many instantaneous current peaks compared with He plasma. For gas flow between 1 and 7 L/min and applied voltage between 3 and 10 kV, no significant changes in Ar plasma are observed. He plasma is found to be sensitive as far as gas flow rate and applied voltage are concerned.
Spectroscopic investigations on a low power atmospheric pressure capacitively coupled helium plasma
2008
An atmospheric pressure helium plasma is characterized based on its optical emission. The plasma is generated at 13.56 MHz (continuous wave) at power levels ranging from 4 to 35 W. It is in contact with a single electrode and is part of a resonant electric circuit. The excitation, vibrational and rotational temperatures are in the range 1880-5660 K, 1960-3150 K and 760-1398 K, respectively. The temperatures are correlated with the plasma power, plasma volume and gas dynamic flow. Atomization and excitation capabilities of the plasma were tested for three easily excitable elements (Zn, Na and Li) introduced in the plasma by pneumatic nebulization from liquid solution.
2010
A cross-flow atmospheric plasma jet with distilled water or analyte solution nebulization has been investigated. The plasma gas flows perpendicularly to the RF powered electrode (11.21 MHz) and a grounded electrode was added for plasma stabilization. The working parameters of the plasma generator can be controlled in order to maximize either the plasma power (75 W) or the voltage on the RF powered electrode (plasma power, 40 W). The plasma gas, pure argon (0.4 l min −1) or a mixture of argon (0.3-0.4 l min −1) and helium (0-0.2 l min −1), was also used for liquid nebulization. Optical emission of the plasma, collected in the normal viewing mode, was used for plasma diagnostics and for evaluating its excitation capabilities. The influence of helium content in the mixed-gas plasma on the plasma characteristics and on the emission axial profiles of the plasma gas constituents and of the analytes originate from the wet aerosol was studied. The addition of helium to the argon plasma, generally determines decreases in the emission of the plasma gas constituents (with the exception of molecular nitrogen), in the rotational temperature and in the electron number density and increases in the excitation temperatures and in the emission of easily excitable analytes. Based on the determined electron number densities, it was concluded that in the plasma zone which presents interest from analytical point of view the plasma is not very far from the partial thermodynamic equilibrium. In function of the helium content in the plasma gas and of the axial distance from the powered electrode the excitation temperatures are in the range of 2420-3340 K for argon, 2500-5450 K for oxygen and 900-2610 K for ionic calcium and the electron number densities are in the range of 1.2 10 12-1.25 10 13 cm −3. Some elements with excitation energy lower than 6 eV were excited in the plasma. The plasma excitation capability depends on the working conditions of the plasma generator (maximum power or maximum voltage on the RF powered electrode) and on the helium content in the mixed-gas plasma. The estimated detection limits for the studied elements (Na, Li, K, Ca, Cu, Ag, Cd, Hg and Zn) are in the range of 7 ng ml −1 to 28 μg ml −1 .
ANALYSIS OF PARAMETERS AND IDENTIFICATION OF CHEMICAL SPECIES PRESENT IN PLASMA JETS FROM THE EXCITATION OF HELIUM AND ARGON FOR DENTAL PURPOSES (Atena Editora), 2024
The study Atmospheric pressure plasma technology has become a prominent area of research due to its diverse applications in health. Areas such as pollution control, materials processing, electrochemistry and engineering as a whole have this technology as very relevant. The moment in which the chemical species in the plasma reach the treated surfaces still requires studies, so the current search aims to obtain deeper knowledge for applications in dentistry. Special attention is paid to the biological and surface effects of plasma-generated reactive species. It is the research aims to use the Optical Emission Spectroscopy (EEO) technique, a tool for plasma diagnosis, detection of reactive species and their identification, as well as the analysis of how they behave according to the parameters adopted in the process. to obtain plasma by Dielectric Barrier Discharge (DBD). To carry out this analysis, it was necessary to follow the steps search of articles to carry out the literature review, laboratory experiments to obtain data and analysis of reactive species. The results include graphs of the plasma spectrum, with its respective parameters, as well as the identification of its chemical species, with thermal images of some samples under incidence of the plasma plume, considered critical for dentistry. It is concluded that the study of reactive species is very important for several areas, especially dentistry, as the chemicals species in addition to carrying out superficial modifications, increasing the applied energy, inactive unwanted microorganisms, with sterilizing effect.
2010
A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5-70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar-He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500-2100 K), He (3000-3500 K) and H (2500-3200 K), the rotational temperature of the OH band (1300-2900 K), the electron temperature (5500-6500 K) and the electron number density (8 • 10 13-2 • 10 14 cm − 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.
Diagnostics of low-pressure hydrogen discharge created in a 13.56 MHz RF plasma reactor
Physica Scripta, 2016
A 13.56 MHz RF discharge in hydrogen was studied within the pressure range of 1-10 Pa, and at power range of 400-1000 W. The electron energy distribution function and electron density were measured by a Langmuir probe. The gas temperature was determined by the Fulcher-α system in pure H2, and by the second positive system of nitrogen using N2 as the probing gas. The gas temperature was constant and equal to 450 ± 50 K in the Capacitively Coupled Plasma mode (CCP), and it was increasing with pressure and power in the Inductively Coupled Plasma mode (ICP). Also the vibrational temperature of ground state of hydrogen molecules was determined to be around 3100 and 2000 ± 500 K in ICP and CCP mode, respectively. The concentration of atomic hydrogen was determined by means of actinometry, either by using Ar (5 %) as the probing gas, or by using H2 as the actinometer in pure hydrogen (Q1 rotational line of Fulcher-α system) The concentration of hydrogen density was increasing with pressure in both modes, but with a dissociation degree slightly higher in the ICP mode (a factor 2).
Spectrochimica Acta Part B: Atomic Spectroscopy, 2017
Using optical emission spectrometry, fundamental properties are investigated of a stable, planar atmospheric pressure micro discharge, several dozen microliters in volume, driven by a digitally controlled 20 kHz rotating microsecond pulsed power. The discharge is generated by rectangular wave pulses using helium as the working gas. At a low cost, the digitally controlled plasma source produces a highly symmetrical, non-stationary helium discharge maintained in open air within 5 electrodes positioned in the plane toward the center. It has been shown that the geometrical shapes of the momentary discharges, which occur between the electrodes, are not arc-like shaped, but rather have a diffusive character and the resulting plasma can become doughnut-like in shape. Rotational and vibrational temperatures from OH and N 2 bands, excitation temperatures from He lines and ionization temperatures from Ca lines, as well as electron number densities from H β Stark broadening have been estimated along the plasma diameter using axial viewing. The results demonstrated that T exc (He) reaches stable value of 3800 K for selected plasma generation conditions (one anode and two cathodes commutation mode, cathode pulse width 8 microseconds, supplied power 200 W, helium gas flow 1 L•min −1), while the T rot (OH) is considerably lower (1700 K). The electron number density has been evaluated to be (1.7-3.3) × 10 14 cm −3 and both T ion (Ca) and T vib (N 2) varied, throughout in the 4500-5100 K and 4000-4800 K ranges respectively, reaching its peak value near 2 mm off the plasma axis. Spatial measurements revealed symmetrical distribution of the plasma parameters, while the measurements of calcium and nitrogen ionic emission confirmed symmetrical doughnut shape of the discharge. Moreover, the processes running inside the discharge and their interaction with the surrounding atmosphere have been described in accordance to the recorded spectra. Spectroscopic observation has shown the existence of N 2 + molecular ions, although their emission profile differs significantly from neutral N 2. Namely, the population of ionic molecules forms a doughnut shape, while the N 2 population exhibits disk shape, indicating that plasma ionization zone is located off-axis.
Review of Scientific Instruments, 1994
A "reference cell" for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.
Spectrochimica Acta Part B: Atomic Spectroscopy, 2004
The radial dependence of the electron density and the gas temperature, two major parameters of the microwave helium plasma produced at atmospheric pressure by the axial injection torch, is presented here. An intensified charge coupled device in combination with an image rotation system allowed to perform laterally resolved emission intensity measurements that were mathematically transformed into radial emissivity using the Abel inversion technique in conjunction with a Smoothing and Interpolation Procedure. When the Abel inversion is not used, only radially averaged values of the electron density and gas temperature values are obtained. The results presented here have been used to obtain the radial range of application of such averaged values. The variation of the radial distribution of these parameters with the incident microwave power and the He flowrate was also obtained. The entrainment of species from the surrounding air into the plasma was also studied in radial terms. Small amounts of O(I), H(I), N(I) and N were found in addition to He(I); this suggests a high entrainment of these elements q 2 from the ambient air into the plasma, which affects the plasma kinetics and the parameter values.