Efficiency Of Plasma Generation Research Articles

Plasma Generated in Hydrodynamic Cavitation Bubbles for the Preparation of Plasma Activated Water

Objective: In recent years, the medical applications of plasma activated water (PAW) have attracted growing interest. PAW can be prepared using plasma generated by hydrodynamic cavitation bubbles (HCB). To facilitate this application, the current study was performed to investigate the efficiency of plasma generation in HCB. Methods: Based on the plasma generated in HCB, an experimental system has been constructed. We measured the characteristics of the cavitating flow, including pressure, temperature, and water flow rate, and estimated the system and cavitation power consumptions. High-speed images of cavitating flow were obtained to examine the evolution of the cavitation zone. Images of discharge emission at various velocities were captured to identify the location of electrodes. In addition, optical emission spectra were examined to determine the type of reactive species. H2O2 concentration and energy efficiency were measured and analyzed. Results: In this experiment, the system power consumption was 1.2W. The highest cavitation power consumption was 50.4W and increased with the elevation of throat velocities. The processing findings of high-speed images revealed that the cavitation characteristic length was essential for plasma generation and was necessary for establishing the location of electrodes. In addition, the UV-Vis emission spectra of the plasma discharge demonstrated that the hydroxyl radical ·OH was formed in situ and that cavitation increased the yield of ·OH. H2O2 was the principal active component of PAW. Plasma generated in HCB produced H2O2 with a high energy efficiency of 77.0mol/kWh. Conclusion: Plasma generated in HCB may provide a viable and cost-effective alternative method for PAW preparation.

Enhanced plasma generation in capacitively coupled plasma using a parallel inductor

Plasma generation efficiency in a capacitively coupled plasma (CCP) at high densities or high conductivity tends to be lower due to low plasma resistance. An inductor is installed to a powered electrode in parallel to improve plasma generation efficiency at higher density in the CCP. To reduce the power loss in a system, a parallel resonance is used between the capacitance of the CCP and the inductance of the parallel inductor. When parallel resonance occurs, the impedance of the chamber, including the plasma, increases. Therefore, the current flowing in the system is expected to decrease. At the resonance, the current in the system significantly decreases, and the voltages and currents at the powered electrode significantly increase. This phenomenon indicates that the system power loss is decreased, and the power absorbed by the plasma is increased. As a result, the ion density and the voltage at the powered electrode are increased up to 66% and 25% at the parallel resonance condition, respectively. To understand these increases, a circuit model for the plasma and the parallel inductor is suggested which shows good agreement with the experimental results. This method can be applied to the CCP for improving plasma generation.

Inductively Coupled Plasma Facilities for Testing of Thermal Protection Materials

This is an overview of existing facilities for testing of thermal protection materials (TPM) for spacecraft based on the inductively plasma (ICP) sources with power over 100 kW. As a chief designer of the ICP plasma torch systems, the author provides the main parameters, describes design of the torches and power supplies, analyzes efficiency of plasma generation, and discusses trends in the ICP-based facilities development with power from 100 kW to 1 MW. The overview is based on data from the open sources and real parameters of APT-100 and −200 plasma systems currently in production by Applied Plasma Technologies, Corporation, Marshall, VA, USA.

A large-area planar helicon plasma source with a multi-ring antenna on Linear Experimental Advanced Device (LEAD)

A planar helicon plasma source with a four-ring antenna has been developed on Linear Experimental Advanced Device (LEAD) in Southwestern Institute of Physics. The diameter of the largest antenna ring is 320 mm. This source is located outside of the vacuum chamber without any vacuum interface and injects radio frequency power into the chamber through a 340-mm-diameter quartz window. A low power threshold of 150 W for electromagnetic-mode to wave-mode transfer is experimentally confirmed. A large volume plasma with a density of over 1019 m−3 and a plasma generation efficiency (total number of electrons diveded by input power) of over 30× 1013 W−1 indicate the high performance of this large-area helicon plasma source, promising LEAD a suitable device for fundamental plasma physics and plasma material interaction research.

Radiation Losses From a Microwave Surface-Wave Sustained Plasma Source (Surfatron)

Surfatron is an electromagnetic (EM) field applicator yielding surface-wave (SW) discharges (SWDs) within dielectric tubes in a broad range of operating conditions. In this article, the vector wave equation for the electric field is solved numerically in 2-D to determine the influence of plasma parameters, such as electron density, normalized electron–neutral collisions frequency, plasma column length and radius, as well as the length of the surfatron body on the field strength distribution, radiation patterns, and ratio of radiated power to power absorbed in plasma. This analysis allows for estimating the efficiency of plasma generation. The model takes into account the surfatron configuration, reproducing the typical SWD plasma column behavior, namely the fact that the plasma column is “pushed out” of the surfatron interstice as absorbed power increases. The surfatron is assumed to be placed in an air-filled sphere with the surface transparent to the wave. Calculations are performed for a field frequency of 2450 MHz and a fused silica tube, considering plasma parameters typical for both atmospheric- and lower-pressure discharge gases for achieving a parametric survey. It is found that for given plasma parameters, varying the plasma column length from a few up to 30 cm significantly affects the distribution of the electric field around the surfatron and the radiation patterns. It is further shown that the radiated to absorbed power ratio increases with increasing electron density and plasma radius, and decreasing electron–neutral collision frequency. This ratio can exceed 30% for a 30-cm plasma column with a plasma radius of 3 mm and parameters typical for atmospheric and reduced gas pressures. The surfatron length at which radiation losses are minimal is at half the vacuum wavelength.

NBR surface modification by gaseous plasma source with electron injection

A gaseous plasma source for materials surface modification has been developed and investigated in detail. The operating pressure range was 6.7 × 10−2 ÷ 2.5 × 10−1 Pa. At discharge current of 10 A and discharge voltage of 100 V the maximum plasma density was up to 3·1010 cm−3 in the volume up to 0.1 m3 in DC mode. The possibility of independent control of the current of injected electrons and their energy, makes it possible to choose the optimal parameters to ensure high energy efficiency of plasma generation (up to 150 eV/ion) according to process requirements and material properties. Using Hughes–Rojansky electrostatic analyzer and moveable Langmuir probe, an electron and ion energy spectra and plasma distribution were measured in the region of substrate location. The source was used for NBR surface modification in the ambient of noble gases, nitrogen, oxygen and acetylene. It has been shown that plasma treatment leads to a decrease in the coefficient of friction of NBR by 2–3 times.

Experimental comparative analysis on series and parallel antenna in an inductively coupled plasma

An experimental comparative analysis of series and parallel antennas was performed in an inductively coupled plasma. For the quantitative comparison of series and parallel antennas on the plasma generation, both antennas were made of copper tubes of the same length and thickness. The power transfer efficiency and the electron energy distribution function were measured. The experimental results show that the series antenna generates higher density plasma due to high coupling at the same applied powers (RF powers), while the parallel antenna generates higher density plasma due to low plasma potential (low ion energy losses) at the same absorbed powers. This provides practical information on plasma generation efficiency according to the antenna configuration of the ICP.

Influence of target structure on laser plasma generation efficiency

Spatial restrictions on heat transfer imposed in foil and sintered powder titanium targets have resulted in sufficient increase of efficiency of laser plasma generation as compared to bulk Ti targets. Especially at low laser fluences, where target material input in plasma is higher than ambient air’s. Also, the pattern of momentum coupling coefficient Cm dependency on laser fluence F has changed from convex to concave. Minimum difference in Cm values for bulk and foil targets was 1.68 times, maximum – 1.5 orders of magnitude (always higher for foil). At the impact on sintered porous targets momentum coupling coefficient was lower than for foil, but normalised by mass density, the results were about equal. To our mind, obtained results show that suppression of heat dissipation in porous targets can be same efficient as in foils, but with more benefits for feeding systems and energy efficiency of laser plasma generators.

Light-curing polymers for laser plasma generation

Solid rather than liquid media are used in pulsed laser plasma generators despite sophisticated transportation and dosing system need for a long-term operation. Liquid media could be more preferable due to transfer and dosing (down to 10-14 L) being well developed, but plasma generation of those results in intense droplet formation and kinetic energy losses. Combination of liquids transportation advantages and solids plasma generation efficiency might resolve this trade-off. Liquid-to-solid transition can be induced by cooling down to sublimation temperature, thermo-, photo- or electron induced polymerization (curing). Light cured polymers seem to be very useful as active media for plasma generators, since they can be solidified very fast (ca. 30 ms) just before impact. We considered experimentally several UV- curing polymer and mixtures ablation regimes and supply schemes for laser plasma generation. The best results were obtained for liquid polymer at high-power pulsed irradiation matching curing optimum wavelength.

Investigation of parameters and uninterrupted service of a generator of gas-discharge plasma based on a nonsustained hot-cathode arc discharge in gas

The design of an electrode system and the characteristics of a gas-discharge plasma source (generator) based on an arc discharge in gas sustained by thermionic emission are presented. The results of an experimental investigation of the service life of a thermionic (hot) cathode of the plasma generator are reported as a function of the discharge current and voltage and the cathode filament power. It is shown that an increase in the burning voltage from 28 to 60 V considerably reduces the service life of the hot cathode, while the discharge current and the cathode filament power exert a less critical effect on its lifetime. The conditions necessary for achieving long-term service life parameters and high efficiency of plasma generation are found out.

Radio frequency discharge with control of plasma potential distribution

A RF discharge plasma generator with additional electrodes for independent control of plasma potential distribution is proposed. With positive biasing of this ring electrode relative end flanges and longitudinal magnetic field a confinement of fast electrons in the discharge will be improved for reliable triggering of pulsed RF discharge at low gas density and rate of ion generation will be enhanced. In the proposed discharge combination, the electron energy is enhanced by RF field and the fast electron confinement is improved by enhanced positive plasma potential which improves the efficiency of plasma generation significantly. This combination creates a synergetic effect with a significantly improving the plasma generation performance at low gas density. The discharge parameters can be optimized for enhance plasma generation with acceptable electrode sputtering.

Advanced Large Volume Surface Plasma H-/D- Source Neutral Beam Injectors

The design of an Advanced Large Volume Surface Plasma Source (LV SPS) for Neutral Beam Injectors is presented and discussed. The LV SPS will be assembled from a set of modules. Every module consists of a plasma generator with an RF saddle antenna injecting plasma and hyperthermal atoms into the expander chamber. The plasma electrode with multi-slit extraction system and localized magnetic filter is attached to the bottom flange of the expander chamber. The plasma will be generated by an RF discharge using a saddle antenna in an optimized longitudinal magnetic field. This type of discharge is very efficient for dense plasma generation. The magnetic field is used to suppress plasma diffusion to the wall, improve the efficiency of plasma generation and decrease the thermal flux to the plasma generator wall. The expanded flux of ions and hyperthermal atoms bombards uniformly the plasma electrodes of the extraction system and produces an intense beam of negative ions. With improved cooling, the average discharge power can be increased significantly above that of any existing SPS. With smaller slit emission apertures, it is possible to suppress H- stripping after extraction. These conditions are promising for reliable production of higher emission current density up to ~40-50 mA/cm2 with corresponding decrease of SPS dimensions and cost.

Time evolution of plasma afterglow produced by femtosecond laser pulses

In this paper we investigate the time evolution of laser plasmas generated in atmospheric air by ultrashort (100fs) laser pulses. The detected quantity is the time integrated photon yield emitted by the plasma, which monotonically depends on the amount of energy transferred by the laser pulses to the plasma. We study the effect of a preionizing pulse on the efficiency of plasma generation by a second “probe” pulse and demonstrate that preionization results into a considerable increase of the overall photon yield emitted by the plasma. An explanation of this phenomenon relies on the fact that the larger the electron density experienced by the probe pulse, the more effective the energy transfer from the probe pulse to the residual plasma, the more intense is the light from the plasma. With this concept in mind and by relying on a pump-probe technique, we also measure the total photon yield emitted by the plasma produced by the combination of the two pulses, as a function of their relative delay time. We observe a considerable increase in the plasma brightness for delay times much longer than the laser pulse duration. This phenomenon is associated with an increase of the electron density even after the end of the pump pulse, due to secondary electron-impact ionization originating from highly-energetic primary photoelectrons, and to superelastic electron-molecule collisions. We also develop a simplified model describing the time evolution of the electron and ion densities and the electron temperature. From the calculated time evolution of these quantities produced by a single laser pulse, we can predict with a good approximation the main features of the plasma generated by an ultrashort laser pulse.

Characteristics of a helicon ion source as a high current density ion source (abstract)

A novel helicon ion source has been developed as a high current density ion source. High plasma generation efficiency of helicon wave lends various high-density, high-temperature plasmas available for ion sources. High-density plasmas of 1012 cm−3 are generated to implement a high current density ion source with 1 kW, 13.56 MHz rf power source. An axial magnetic field of up to 900 G has been applied with a set of permanent magnets to make the helicon wave propagate. Various gaseous ion beams have been extracted with this source. Beam characteristics such as ion energy spread and ionic charge states will be discussed with the plasma parameters.

Generation of a homogeneous large cross section ion beam in a magnetically insulated diode

The paper is dedicated to the studies of ion beam generation in a ribbon type magnetically insulated diode with special attention to the electron losses on the anode. Several modifications of this type of diode resulted in a very low level of these losses and a high degree of beam homogeneity. At the same time the low plasma generation efficiency demonstrates the important role of electron bombardment for its production.