The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications ...The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.展开更多
In this work,a bright and dark concentric-ring pattern is reported in a dielectric barrier discharge for the first time.The spatiotemporal dynamics of the bright and dark concentric-ring pattern are investigated with ...In this work,a bright and dark concentric-ring pattern is reported in a dielectric barrier discharge for the first time.The spatiotemporal dynamics of the bright and dark concentric-ring pattern are investigated with an intensified charge-coupled device and photomultiplier tubes.The results indicate that the bright and dark concentric-ring pattern is composed of three concentric-ring sublattices.These are bright concentric-ring structures,dark concentric-ring structures and wider concentric-ring structures,respectively.The bright concentric-ring structures and dark concentricring structures are alternately distributed.The bright concentric-ring structures are located at the centre of the wider concentric-ring structures.The wider concentric-ring structures first form from the outer edge and gradually develop to the centre.The essence of all three concentric-ring structures is the individual discharge filaments.The optical emission spectra of different sublattices are acquired and analysed.It is found that the plasma parameters of the three concentricring sublattices are different.Finally,the formation mechanism of the bright and dark concentricring pattern is discussed.展开更多
The surface charge characteristics in a three-electrode surface dielectric barrier discharge(SDBD)are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the...The surface charge characteristics in a three-electrode surface dielectric barrier discharge(SDBD)are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the most commonly used SDBD structure for airflow control, with an exposed electrode supplied with sinusoidal AC high voltage, a grounded encapsulated electrode and an additional exposed electrode downstream supplied with DC voltage. The ionic wind velocity and thrust can be significantly improved by increasing DC voltage although the plasma discharge characteristics are virtually unaffected. It is found that the negative charges generated by the discharge of the three-electrode structure accumulate on the dielectric surface significantly further downstream in an AC period compared to the actuator with a two-electrode structure. The negative charges in the downstream region increase as the DC voltage increases.In addition, the DC voltage affects the time required for the positive charge filaments to decay.The positive DC voltage expands the ionic acceleration zone downstream to produce a greater EHD force. The amplitude of the DC voltage affects the electric field on the dielectric surface and is therefore a key factor in the formation of the EHD force. Further research on the surface charge characteristics of a three-electrode structure has been conducted using a pulse power to drive the discharge, and the same conclusions are drawn. This work demonstrates a link between surface charge characteristics and EHD performance of a three-electrode SDBD actuator.展开更多
Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning imp...Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline(stage 1), rapid velocity rise(stage 2)and slow velocity decline(stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.展开更多
Dielectric barrier discharge(DBD)plasma actuators are widely used in active flow control due to their simple design and rapid responsiveness.However,they need more effectiveness and discharge extension.To overcome the...Dielectric barrier discharge(DBD)plasma actuators are widely used in active flow control due to their simple design and rapid responsiveness.However,they need more effectiveness and discharge extension.To overcome these limitations,a sector-shaped dielectric barrier discharge(SS-DBD)plasma actuator with an adjustable jet angle was developed to enhance flow control effectiveness.The flow field dynamics induced by the SS-DBD plasma actuator were quantitatively analyzed using particle image velocimetry(PIV).Experimental investigations showed that precise adjustments to the actuation voltage can modulate the maximum velocity of the induced jet.Furthermore,a quasi-linear relationship between the sector-shaped angles of the SS-DBD and the deflected jet angles was established,indicating that changes in the sector-shaped angles directly influence the direction of the deflected jet.This correlation enables precise control over jet angles,significantly enhancing flow control by adjusting the SS-DBD-PA's sector-shaped angle.展开更多
Archimedean photonic crystal has become a research area of great interest due to its various unique properties. Here, we experimentally demonstrate the realization of reconfigurable(4, 6^(2))and(4, 8^(2)) Archimedean ...Archimedean photonic crystal has become a research area of great interest due to its various unique properties. Here, we experimentally demonstrate the realization of reconfigurable(4, 6^(2))and(4, 8^(2)) Archimedean plasma photonic crystals(APPCs) by use of dielectric barrier discharges in air. Dynamical control on both the macrostructures including the lattice symmetry and the crystal orientation, and the microstructures including the fine structures of scattering elements has been achieved. The formation mechanisms of APPCs are studied by time-resolved measurements together with numerical simulations. Large omnidirectional band gaps of APPCs have been obtained. The tunable topology of APPCs may offer new opportunities for fabricating multi-functional and highly-integrated microwave devices.展开更多
基金supported by National Natural Science Foundation of China (No. 12075132)。
文摘The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.
基金supported by National Natural Science Foundation of China(No.12075075)the Natural Science Foundation of Hebei Province,China(Nos.2020201016,A2018201154,A2023201012)Scientific Research and Innovation Team of Hebei University(No.IT2023B03)。
文摘In this work,a bright and dark concentric-ring pattern is reported in a dielectric barrier discharge for the first time.The spatiotemporal dynamics of the bright and dark concentric-ring pattern are investigated with an intensified charge-coupled device and photomultiplier tubes.The results indicate that the bright and dark concentric-ring pattern is composed of three concentric-ring sublattices.These are bright concentric-ring structures,dark concentric-ring structures and wider concentric-ring structures,respectively.The bright concentric-ring structures and dark concentricring structures are alternately distributed.The bright concentric-ring structures are located at the centre of the wider concentric-ring structures.The wider concentric-ring structures first form from the outer edge and gradually develop to the centre.The essence of all three concentric-ring structures is the individual discharge filaments.The optical emission spectra of different sublattices are acquired and analysed.It is found that the plasma parameters of the three concentricring sublattices are different.Finally,the formation mechanism of the bright and dark concentricring pattern is discussed.
基金supported by National Natural Science Foundation of China (Nos. 51777026 and 11705075)。
文摘The surface charge characteristics in a three-electrode surface dielectric barrier discharge(SDBD)are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the most commonly used SDBD structure for airflow control, with an exposed electrode supplied with sinusoidal AC high voltage, a grounded encapsulated electrode and an additional exposed electrode downstream supplied with DC voltage. The ionic wind velocity and thrust can be significantly improved by increasing DC voltage although the plasma discharge characteristics are virtually unaffected. It is found that the negative charges generated by the discharge of the three-electrode structure accumulate on the dielectric surface significantly further downstream in an AC period compared to the actuator with a two-electrode structure. The negative charges in the downstream region increase as the DC voltage increases.In addition, the DC voltage affects the time required for the positive charge filaments to decay.The positive DC voltage expands the ionic acceleration zone downstream to produce a greater EHD force. The amplitude of the DC voltage affects the electric field on the dielectric surface and is therefore a key factor in the formation of the EHD force. Further research on the surface charge characteristics of a three-electrode structure has been conducted using a pulse power to drive the discharge, and the same conclusions are drawn. This work demonstrates a link between surface charge characteristics and EHD performance of a three-electrode SDBD actuator.
基金supported by the Beijing Science Fund for Distinguished Young Scholars(No.JQ22009)National Natural Science Foundation of China(No.51977198)。
文摘Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline(stage 1), rapid velocity rise(stage 2)and slow velocity decline(stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.
基金supported by National Natural Science Foundation of China(Nos.61971345 and 52107174)。
文摘Dielectric barrier discharge(DBD)plasma actuators are widely used in active flow control due to their simple design and rapid responsiveness.However,they need more effectiveness and discharge extension.To overcome these limitations,a sector-shaped dielectric barrier discharge(SS-DBD)plasma actuator with an adjustable jet angle was developed to enhance flow control effectiveness.The flow field dynamics induced by the SS-DBD plasma actuator were quantitatively analyzed using particle image velocimetry(PIV).Experimental investigations showed that precise adjustments to the actuation voltage can modulate the maximum velocity of the induced jet.Furthermore,a quasi-linear relationship between the sector-shaped angles of the SS-DBD and the deflected jet angles was established,indicating that changes in the sector-shaped angles directly influence the direction of the deflected jet.This correlation enables precise control over jet angles,significantly enhancing flow control by adjusting the SS-DBD-PA's sector-shaped angle.
基金supported by National Natural Science Foundation of China(Nos.12275065 and 11975089)Natural Science Foundation of Hebei Province(Nos.A2021201010 and A2021201003)+4 种基金Interdisciplinary Research Program of Natural Science of Hebei University(No.DXK202108)Hebei Provincial Central Government Guiding Local Science and Technology Development Funds(No.236Z1501G)Scientific Research and Innovation Team Foundation of Hebei University(No.IT2023B03)The Excellent Youth Research Innovation Team of Hebei University(No.QNTD202402)Regional Key Projects of National Natural Science Foundation of China(No.U23A20678).
文摘Archimedean photonic crystal has become a research area of great interest due to its various unique properties. Here, we experimentally demonstrate the realization of reconfigurable(4, 6^(2))and(4, 8^(2)) Archimedean plasma photonic crystals(APPCs) by use of dielectric barrier discharges in air. Dynamical control on both the macrostructures including the lattice symmetry and the crystal orientation, and the microstructures including the fine structures of scattering elements has been achieved. The formation mechanisms of APPCs are studied by time-resolved measurements together with numerical simulations. Large omnidirectional band gaps of APPCs have been obtained. The tunable topology of APPCs may offer new opportunities for fabricating multi-functional and highly-integrated microwave devices.
