The first challenge in Low-Temperature Plasma Physics is “Atmospheric Pressure Nonequilibrium Plasma (APNP)”.
At one atmospheric pressure and room temperature, the molecular/atom density of gas is about 2.4×10
19cm
-3. For electron temperature of few electron volts range, the electron-neutral collision frequency is on the order of 10
10 to 10
12/s range, so the electron can quickly transfer its energy to molecular/atom and result in thermal equilibrium plasma when it receives energy from the electric field. Thus it is extremely difficult to obtain nonequilibrium plasma at atmospheric pressure. To obtain APNP, in general, there are two major strategies, one is limiting the discharge lasting time, which can be achieved by using a short voltage pulse to drive the plasma, or by inserting a dielectric in the circuit; this is widely known as dielectric barrier discharge (DBD). Another strategy is confining the discharge within a small space, so the plasma has a large surface-volume ratio, which is favorable for cooling the plasma and is frequently referred to as micro plasma. Certainly, there are several other methods that are used to generate APNP, such as gliding arc discharge, transit spark discharge, and so on.
For APNP, because its gas temperature is significantly lower than its electron temperature, the plasma has an enhanced chemical reactivity compared to the gas at the same gas temperature. The electron could excite the molecules to higher excitation and vibrational states, or even break chemical bonds through electron collision. In such a way, certain chemical reactions are enhanced and intended chemical products can be obtained at relatively low gas temperatures.
Several emerging applications of APNP, such as plasma for CO
2 conversion, nitrogen fixation, and plasma medicine, are attracting lots of attention in the past decades. However, before these applications can be realized, there are several big unanswered questions in the field needing to be addressed - these include:
(1) how the energy is temporally distributed among rotation/vibration/excitation/ionization paths for different plasma sources and how to control among the paths;
(2) what are the preferred plasma sources for various plasma applications?;
(3) how to develop suitable plasma sources for specific applications;
(4) how to obtain the full picture of the spatial and temporal resolved plasma characteristics;
(5) what will be the new potential applications of APNP in the following decade?
The Specialty Chief Editor would like to invite critical, ambitious, and courageous contributions, covering theoretical, conceptual, empirical, or computational research, that can provide new insights and stimulate a constructive debate around the open questions mentioned above.
The Research Topic solicits contributions from the Editorial Board members of the Low-Temperature Plasma Physics section.
-Article types: Brief Research Report, Original Research, Review, Mini Review, Perspective…
The Specialty Chief Editors of Frontiers in Physics launch a new series of Research Topics to highlight current challenges across the field of Physics. Other titles in the series are:
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Editor's Challenge in Quantum Engineering and Technology: Economic Impact and Perspectives of Quantum Technologies
Editor’s Challenge in Soft Matter Physics: Where Is Soft Matter Physics Going?
Editor's Challenge in Optics and Photonics: Advancing Electronics with Photonics
Editor’s Challenge in High Energy and Astroparticle Physics: Is The W Mass Anomaly Real?
Editor’s Challenge in Fluid Dynamics: Flows Across the Scales