Jing Li

Selective control of the key parameters of the cold atmospheric plasmas (CAPs) is crucial for diverse applications ranging from materials processing, clinical medicine to clean energy generation. In particular, the low gas temperature ( T _g ) and high electron number density ( n _e ) are both critical for obtaining high treatment efficiency of heat-sensitive materials, yet are challenging to achieve because of the very frequent species collision nature in CAPs. In this paper, selective control of T _g and n _e in a helium CAP driven by a radio-frequency power supply and operated in an open environment is achieved successfully for the first time numerically and experimentally with the quasi-independent variation windows from −33.7 °C to 49.5 °C (i.e. 239.3 to 322.5 K) for T _g and from 2.7 × 10 ¹⁶ to 6.3 × 10 ¹⁶ m ⁻³ for n _e . This result has expanded the key CAP parameter windows significantly into a previously unachievable domain. The further theoretical analysis of the energy transfer and balance based on the ‘energy tree’ concept and numerical modeling reveals the unique non-equilibrium energy transfer channel allowing selective control of T _g and n _e . This energy transfer channel is enabled by the two ‘valves’, one for controlling the energy deposition from the external circuit to the discharge cell (valve 1), and another one for controlling the energy exchange between the discharge cell and the environment (valve 2). Our conceptual approach and proof-of-principle demonstration open a new way for the active and selective control of the key CAP parameters, which will be quite important for designing CAP sources with specific requirements and for advancing or even creating new CAP applications in the future.

During discharges of an arc plasma, complex mass, momentum and energy exchanges exist between the arc column and the surrounding cold gas, forming a nonequilibrium region deviating from both the local thermodynamic equilibrium and local chemical equilibrium states. The nonequilibrium synergistic transport plays a crucial role not only in controlling the characteristics of the arc plasmas theoretically, but also in optimizing the plasma material processing qualities in actual applications. In this paper, the nonequilibrium transport processes in free-burning argon arc plasmas under different operating pressures and arc currents are studied based on a complete nonequilibrium fluid model, and are also validated by comparing with measured data. The energy transfer processes under various operating conditions, especially Joule heating, elastic and inelastic collisions, conductive and convective heat transfer, and energy transfer related to the temperature ratio spatial gradient, are analyzed based on the concept of the ‘energy tree.’ The revealed major energy transfer channels in the high-pressure argon arc plasmas also provide some possibilities to control the characteristics of thermal plasmas in the future.

Cold atmospheric plasmas (CAPs) used in plasma medicine have shown great potential in various aspects including wound healing, dermatology, cancer therapy, etc. It is one of the important issues to determine the plasma dosage in plasma medicine because it dominates the specific plasma treatment results. However, the multi-process interactions between CAPs and biological materials make it rather challenging to give an accurate and versatile definition for plasma dosage. In this study, the ratio of the discharge energy to the number of the treated in vitro kidney cells (mJ/cell) was employed as the unit of the plasma dosage. Additionally, inspired by basic knowledge of pharmacy, the median lethal dose (LD₅₀) was employed to help estimate the plasma dosage. The experimental results show that the value of LD₅₀ using the newly designed CAP Bio-Med Platform for the kidney cells is 34.67 mJ/cell. This biology-based method has the advantages of easy operation, independence of specific CAP sources, and also independence of complex interactions between CAPs and the treated biological targets, and consequently, may provide a new direction to quantitatively define the plasma dosage in various plasma medical applications.

Surgical incision infection of multidrug-resistant microorganisms (e.g., methicillin-resistant Staphylococcus aureus , MRSA) is a severe cause of poor wound healing, which is prevalent in healthcare facilities and constitutes a huge infectious disease burden in the world. The purpose of this study is to investigate the medical application and possible mechanisms of the cold atmospheric plasma jet on infected wounds. In this article, the New Zealand rabbit in vivo wound infected with MRSA is used as the wound healing animal model. The helium atmospheric-pressure dielectric-barrier-discharge (AP-DBD) plasma jet is employed to treat the wounds infected with MRSA. The wound healing, histological, and cytokine analyses are conducted to evaluate the efficacy of the helium AP-DBD plasma jet on the MRSA-infected wound healing process. The experimental results show that the helium AP-DBD plasma jet treatment on the wounds infected with MRSA can regulate the secretion of the cytokines, limit the inflammatory response and cell excessive proliferation, accelerate the process of re-epithelialization, and consequently, promote the wound healing process and the inactivation of the bacteria.

Determination of the key chemical reaction pathways in cold atmospheric plasmas (CAPs) is of great importance not only for understanding the spatiotemporal evolutions of the key plasma parameters during discharges but also for improving the plasma materials processing qualities. In this paper, a novel chemical reaction reduction method (CRRM) is proposed by using the global fluid model coupled with the genetic algorithm and the dynamic programming technique. With the aid of this newly developed CRRM, the key chemical reaction pathways can be automatically screened with a high computational efficiency under a pre-set critical calculation accuracy for the atmospheric pure helium and helium–nitrogen glow discharge plasmas. By comparing the calculated key plasma parameters, e.g., the species number densities, electron temperatures, voltage–current characteristics, based on the simplified models and their corresponding full models with those of the experimentally measured data, the reliability of the CRRM itself and the established key chemical reaction database for the atmospheric pure helium and helium–nitrogen CAPs are validated. This research also provides a general method for screening the key chemical reaction pathways for various low-temperature plasma sources.

It is a useful method to lengthen the cold atmospheric plasma jet with the aid of gas shielding. In this paper, the interactions between the shielding gas and the radio-frequency atmospheric-pressure glow discharge plasma jet are studied numerically and experimentally. The modeling results show that both the chemical compositions and flowrates of the shielding gas strongly influence the characteristics of the plasma jets. A long helium-shielding plasma jet with a length of 34-35 mm is obtained. The predicted lengths of the plasma shielding jets under specified operating conditions are qualitatively consistent with the experimental measurements.