Low-temperature Plasma Devices Research Articles

A birdcage resonant antenna for helicon wave generation in TORPEX.

A birdcage resonant helicon antenna is designed, mounted, and tested in the toroidal device TORPEX. The birdcage resonant antenna is an alternative to the usual Boswell or half-helical antenna designs commonly used for ∼10 cm diameter helicon sources in low temperature plasma devices. The main advantage of the birdcage antenna lies in its resonant nature, which makes it easily operational even at large scales, an appealing feature for the TORPEX device whose poloidal cross section is 40cm in diameter. With this antenna, helicon waves are shown to be launched and sustained throughout the whole torus of TORPEX. The helicon waves can be launched at low power on a pre-existing magnetron-generated plasma with little effect on the density profiles. The birdcage antenna can also be used alone to produce plasma, which removes the constraint of a narrow range of applied magnetic fields required by the magnetron, opening the way to a new range of studies on TORPEX with the external magnetic field as a control parameter.

Experimental assessment of low temperature plasma devices for bacterial aerosol inactivation in the air duct of HVAC systems.

In light of growing concerns about indoor air quality and the transmission of pathogens, this study aims to evaluate the effectiveness of low temperature plasma (LTP) devices in inactivating bacterial aerosols in the air duct of HVAC systems, exploring methods to enhance air purification efficiency. This research employed experimental methods to explore the deactivation effects of LTP on common bacteria such as E. coli and Bacillus subtilis, focusing on the role of air parameters such as the airflow rate, relative humidity, and temperature in influencing the device's performance. Notably, the study determined that an operational voltage of 3000 V for the LTP device, combined with conditions of low airflow, low humidity, and high temperature, significantly enhances the inactivation of bacterial aerosols, achieving an 82% inactivation rate at a negative ion concentration of 2.4 × 1011 ions per m3 and a wind speed of 3 m s-1. Despite the generation of ozone and ultraviolet light as by-products, their concentrations were found to be within safe limits for human exposure. In addition, this study identified an effective inactivation range, alongside an optimal arrangement for the airflow direction within ducts, to maximize the sterilization efficiency of the LTP device. Given these promising results, the study advocates for the integration of LTP technology into the air duct of HVAC systems of public buildings to improve air quality and reduce the risk of airborne disease transmission.

Bench test of interferometer measurement for the Keda Reconnection eXperiment device (KRX)

Motivated by the need of the electron density measurement for the Keda Reconnection eXperiment (KRX) facility which is under development, an interferometer system has been designed and tested in bench. The 320 GHz solid-state microwave source with 1 mm wavelength is used to fulfill the high phase difference measurement in such low temperature plasma device. The results of the bench test show that the phase difference is accurately measured. In contrast to tens of degrees of phase shift expected to be measured on the KRX, the system noise (∼1°) is low enough for the KRX diagnostics. In order to optimize the system for better performance, we utilize the Terasense sub-THz imaging system to adjust alignment. The interferometer system has also been calibrated via changing of the optical path length controlled by the piezo inertial motor. Simultaneously, high density polyethylene thin film is introduced successfully to change a tiny phase difference and test the sensitivity of the interferometer system.

Introduction of N-containing moieties by ammonia plasma technique can substantially improve ciprofloxacin removal by biochar and the associated mechanisms: Spectroscopic and site energy distribution analysis

A low-temperature plasma device was developed to introduce N-containing moieties into biochar type CS-300 to improve ciprofloxacin removal. The sorption capacity of ciprofloxacin by the treated biochars was 2.61–4.26 times that of CS-300, and the mechanisms were explained by X-ray photoelectron spectroscopy and site energy distribution analysis. The results showed that the π-π stacking mechanism dominated ciprofloxacin removal by biochars. Ammonia-plasma treatment introduced abundant amino and amide groups to CS-300. They increased the π electron density in the delocalized system in CS-300, thus enhancing ciprofloxacin removal by the π-π stacking mechanism. Plasma treatment also enhanced polar interactions between ciprofloxacin and CS-300 through hydrogen- and ionic bonding occurring at high-energy sites with energy over 10,000 J/mol, thereby increasing ciprofloxacin removal. The maximum removal efficiency of ciprofloxacin by the treated biochars reached 71.0–85.7% at pH 6, while that for CS-300 was only 31.6% and occurred at pH 4. This implied that plasma treatment not only greatly increased the maximum removal efficiency but also shifted the optimal pH from acidic to nearly-neutral condition. Our findings highlight that ammonia-plasma treatment is a promising technique to improve ciprofloxacin removal by biochars and the treated biochars have potential applications in its removal from water.

A novel atmospheric-pressure air plasma jet for wound healing.

Current low‐temperature plasma (LTP) devices essentially use a rare gas source with a short working distance (8 to 20 mm), low gas flow rate (0.12 to 0.3 m3/h), and small effective treatment area (1‐5 cm2), limiting the applications for which LTP can be utilised in clinical therapy. In the present study, a novel type of LTP equipment was developed, having the advantages of a free gas source (surrounding air), long working distance (8 cm), high gas flow rate (10 m3/h), large effective treatment area (20 cm2), and producing an abundance of active substances (NOγ, OH, N2, and O), effectively addressing the shortcomings of current LTP devices. Furthermore, it has been verified that the novel LTP device displays therapeutic efficacy in terms of acceleration of wound healing in normal and Type I diabetic rats, with enhanced wound kinetics, rate of condensation of wound area, and recovery ratio. Cellular and molecular analysis indicated that LTP treatment significantly reduced inflammation and enhanced re‐epithelialization, fibroblast proliferation, deposition of collagen, neovascularization, and expression of TGF‐β, superoxide dismutase, glutathione peroxidase, and catalase in Type I diabetic rats. In conclusion, the novel LTP device provides a convenient and efficient tool for the treatment of clinical wounds.

A map of control for cold atmospheric plasma jets: From physical mechanisms to optimizations

The study of cold atmospheric plasma (CAP) began about a decade ago. Currently, multiple applications of CAP have been discovered including biomedicine, nanomaterials, agriculture, and water purifications. At the current stage of these research fields, it is obvious that the next move will be CAP optimization for each specific application. For example, in the field of plasma-based cancer treatment, due to the different responses of cell lines, CAP can activate different biological pathways in different cells, i.e., to be selective. One of the most commonly used CAP types is the cold atmospheric plasma jet (CAPJ). However, without a full understanding of CAPJ physics, it is impossible to optimize the plasma for every application condition. Moreover, since each research team is equipped with its own CAPJ generator, the hardware behaviors vary significantly across researchers. Therefore, a complete big picture of CAPJ control and parameters is a critical milestone for future CAPJ optimization in these research fields. This Review provides a summary of how CAPJ parameters can be manipulated with the control inputs and hardware design to extend that the chemical compositions can be modified by the gas flow rate, discharge waveform, target properties, and local environment. Based on the control map summarized in this work, CAPJ users can easily optimize their device for a certain specific purpose, such as maximizing OH and H2O2 for cancer treatment or maximizing O3 and ultraviolet for sterilization. Therefore, this study sheds light on the general theory of CAPJ control and can be a basis for future optimization of low-temperature plasma devices. Consideration of the plasma control based on machine learning methods has been receiving interest recently and certainly will become a future hot topic.

A 14-moment maximum-entropy description of electrons in crossed electric and magnetic fields

A 14-moment maximum-entropy system of equations is applied to the description of non-equilibrium electrons in crossed electric and magnetic fields and in the presence of low collisionality, a characteristic of low-temperature plasma devices. The flexibility of this formulation is analyzed through comparison with analytical results for steady-state non-equilibrium velocity distribution functions and against particle-based solutions of the time-dependent kinetic equation. Electric and magnetic source terms are derived for the 14-moment equations, starting from kinetic theory. A simplified collision term based on the Bhatnagar–Gross–Krook operator is formulated to describe the collision of electrons with background neutrals, accounting for the large mass disparity and energy exchange. An approximated expression is proposed for the collision frequency, to include the effect of the electrons' drift velocity, showing good accuracy in the considered conditions. The capabilities of the proposed 14-moment closure to accurately capture the non-equilibrium behavior of electrons for space homogeneous problems under conditions representative of those found in Hall thrusters are demonstrated.

Theory of a cylindrical Langmuir probe parallel to the magnetic field and its calibration with interferometry

A theory for data interpretation is presented for a cylindrical Langmuir probe in plasma parallel to the magnetic field direction. The theory is tested in a linear low-temperature plasma device Aline, in a capacitive radio-frequency (RF) discharge. The probe is placed on a 3D manipulator, and a position scan is performed. To exclude strong RF perturbations, the probe is RF compensated. Using the theory, electron densities are obtained from the current at the plasma potential, where no sheath is present. Results are calibrated by line-integrated density measurements of a 26.5 GHz microwave interferometer. Reasonable agreement is observed for probe and interferometer measurements. Furthermore, preceding, more general probe theory is compared to the one developed in the current work and the application limits are discussed.

Rotating structures in low temperature magnetized plasmas—insight from particle simulations

The EXB configuration of various low temperature plasma devices is often responsible for the formation of rotating structures and instabilities leading to anomalous electron transport across the magnetic field. In these devices, electrons are strongly magnetized while ions are weakly or not magnetized and this leads to specific physical phenomena that are not present in fusion plasmas where both electrons and ions are strongly magnetized. In this paper we describe basic phenomena involving rotating plasma structures in simple configurations of low temperature EXB plasma devices on the basis of PIC-MCC (Particle-In-Cell Monte Carlo Collisions) simulations. We focus on three examples: rotating electron vortices and rotating spokes in cylindrical magnetrons, and azimuthal electron-cyclotron drift instability in Hall thrusters. The simulations are not intended to give definite answers to the many physics issues related to low temperature EXB plasma devices but are used to illustrate and discuss some of the basic questions that need further studies.

Oral bacterial inactivation using a novel low-temperature atmospheric-pressure plasma device

Background/purposeAtmospheric-pressure plasma is a new technology for biomedical applications. Utilization of an ionized gas (plasma) to achieve disinfection is an alternative sterilization technique that has become popular recently due to its safety, cost effectiveness, and superior performance to traditional methods. The purpose of this study was to evaluate the germicidal effectiveness of a low-temperature atmospheric-pressure plasma device by treating Enterococcus faecalis for different durations. Materials and methodsA novel low-temperature atmospheric-pressure plasma device was developed for this study. A suspension of E. faecalis (BCRC 10789) was standardized to 107 colony-forming units (CFUs)/mL, as confirmed by an optical spectrophotometer. E. faecalis was first transferred and spread on 70 sterile cover glasses measuring 18 mm2. Each batch of 10 specimens was exposed to the low-temperature plasma device and treated for 1 minute, 2 minutes, 3 minutes, 5 minutes, 10 minutes, and 15 minutes; the specimen treated for 0 minute served as the control. The cover glasses containing plasma-treated bacteria were then immersed into 10 mL deionized distilled water and vibrated with an ultrasonic device to detach the residual fluid. Bacterial colonies were finally inoculated into Luria–Bertani agar plates and cultured at 37°C for 24 hours. The numbers of bacterial colonies were counted to evaluate the germicidal efficacy of the plasma device, and the results were expressed as CFUs. Meanwhile, field emission scanning electron microscopy was performed to observe the cell morphology of E. faecalis prior to and after plasma treatment. ResultsQuantitative analysis of sterilization revealed a reduction in the number of bacterial colonies with time duration. When specimens were treated for 10 minutes, colonies of E. faecalis decreased from 105 CFUs to 102 CFUs. The sterilization D-value (90% cell reduction) of experiments was 2 minutes. ConclusionThe novel low-temperature atmospheric-pressure device was capable of achieving effective sterilization of E. faecalis within a 2-minute interval. Further studies are needed to validate complete inactivation, refine the laboratory-made low-temperature plasma device, and develop a new plasma-jet device, which will be superior to traditional sterilization methods and can be used in root canal environment. This novel sterilization method can also be used as a clinical reference tool.

Low-temperature atmospheric plasma increases the expression of anti-aging genes of skin cells without causing cellular damages

Efforts to employ various types of plasma in the field of skin care have increased consistently because it can regulate many biochemical reactions that are normally unaffected by light-based therapy. One method for skin rejuvenation adopted a high-temperature plasma generator to remove skin epithelial cells. In this case, the catalyzing effects of the plasma were rarely used due to the high temperature. Hence, the benefits of the plasma were not magnified. Recently, many types of low-temperature plasma devices have been developed for medical applications but their detailed functions and working mechanisms are unclear. The present study examined the effect of low-temperature microwave plasma on skin cells. Treatment with low-temperature plasma increased the expression of anti-aging genes in skin cells, including collagen, fibronectin and vascular endothelial growth factor. Furthermore, the plasma treatment did not cause cell death, but only induced slight cell growth arrest at the G2 phase. Although the cells treated with low-temperature plasma showed moderate growth arrest, there were no signs of thermal or genetic damage of skin cells. Overall, this low-temperature microwave plasma device induces the expressions of some anti-aging-related genes in skin cells without causing damage.

Plasmas in Tooth Root Canal

Using the plasma generated inside the root canal rather than the afterglow of the plasma will significantly improve the inactivation efficiency. In this paper, images of three kinds of atmospheric-pressure low-temperature plasma devices driven by different power supplies in the tooth root canal are reported. The images of an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> -needle device driven by a dc power supply inside the root canal using different gases (He, Ar, and surrounding air) are also presented.

The Influence on Hydrophilic after the Surface Treatment of the Singed Gray Fabric by the Low Temperature Plasma

We carried on the surface treatments to the cotton fabric (singed and hadn't been singed) with the low temperature plasma device. We studied the desizing performances, compared the capillaries. The results showed that after the same plasma treatment, the intensity of the singed hydrophilic was similar to those that hadn't been singed yet. We also explained the influence on hydrophilic, the results provide a scientific basis for the using of the pretreatment plasma technique in the future.

Influence of the microstructure on the deuterium retention in tungsten

The microstructure of tungsten samples is systematically modified by recrystallization to investigate the structure dependence of deuterium (D) retention. After a thorough characterization by scanning and transmission electron microscopy, non-recrystallized samples and samples recrystallized by different degrees are loaded with deuterium in a low-temperature plasma device. The deuterium inventory is measured by nuclear reaction analysis and thermal desorption spectroscopy. The post implantation surface morphology is investigated by scanning electron, optical and atomic force microscopy. The modification by recrystallization allows a wide variation in the crystallite size and has a strong impact on the measured D retention. Both the total amount and the binding state of the retained D are changed.

Treatment of Candida albicans biofilms with low-temperature plasma induced by dielectric barrier discharge and atmospheric pressure plasma jet

Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice.

A Novel Continuously Initiated Polymerization by One-Atmosphere Low Temperature Plasma Device

A novel atmospheric plasma device developed in this paper, which is more effective and convenient to study the plasma-initiated polymerization (PIP) than conventional setup. The structure and mechanism of the device is introduced. Some plasma-initiated polymerization experiments are carried out on the device, and the conversion of AA (Acrylic acid) and AM (Acryl amide) atmospheric (N2) plasma polymerization are respectively 89% and 94% after 120 h post polymerization, whereby IR spectra of the product (AA, AM). Our PIP result are confirmed.

Temperature-gradient-driven flows of ions and neutrals in dusty plasmas

Abstract It is shown that in low-temperature plasma devices with pulsed external current circuits such as thermal emission converters and plasma diodes, the only forces inducing plasma flows are due to the temperature stresses on ions. These flows are similar to the plasma “residual” rotations in tokamaks. However, they are connected with the perpendicular viscosity dependence of the ion heat fluxes, contrary to tokamaks where parallel viscosity plays the main role. Dust contamination of these devices can induce temperature-gradient driven flows of ions, which also entrain neutrals in a multi-component partially ionized plasma.