Radio frequency capacitively coupled plasma source(RF-CCP)with a hollow electrode can increase the electron density through the hollow cathode effect(HCE),which offers a method to modify the spatial profiles of the pl...Radio frequency capacitively coupled plasma source(RF-CCP)with a hollow electrode can increase the electron density through the hollow cathode effect(HCE),which offers a method to modify the spatial profiles of the plasma density.In this work,the variations of the HCE in one RF period are investigated by using a two-dimensional particle-in-cell/Monte-Carlo collision(PIC/MCC)model.The results show that the sheath electric field,the sheath potential drop,the sheath thickness,the radial plasma bulk width,the electron energy distribution function(EEDF),and the average electron energy in the cavity vary in one RF period.During the hollow electrode sheath's expansion phase,the secondary electron heating and sheath oscillation heating in the cavity are gradually enhanced,and the frequency of the electron pendular motion in the cavity gradually increases,hence the HCE is gradually enhanced.However,during the hollow electrode sheath's collapse phase,the secondary electron heating is gradually attenuated.In addition,when interacting with the gradually collapsed hollow electrode sheaths,high-energy plasma bulk electrons in the cavity will lose some energy.Furthermore,the frequency of the electron pendular motion in the cavity gradually decreases.Therefore,during the hollow electrode sheath's collapse phase,the HCE is gradually attenuated.展开更多
Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the...Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the dynamic range of operation voltage, repetition frequencies and lifetime of switch. The unique feature of pseudospark switch is its hollow cathode geometry. The hollow cathode effect produced by the hollow cathode provides the protection of the switch for the triggering unit from erosion by high discharge plasma. In this paper, a zinc oxide (ZnO) surface flashover triggering is presented. This trigger unit possesses an excellent time delay (80 ns - 360 ns) and jitter (20 ns - 50 ns) at the switch voltage of 30 kV - 2 kV. The emitted plasma electron density is high enough to trigger switch reliably down to switch voltage of 440 V.展开更多
To investigate the galvanic corrosion behavior of a copper(Cu)-304 stainless steel curved surface coupling system in a chloride-containing acidic environment,wire beam electrode(WBE)technology was innovatively integra...To investigate the galvanic corrosion behavior of a copper(Cu)-304 stainless steel curved surface coupling system in a chloride-containing acidic environment,wire beam electrode(WBE)technology was innovatively integrated with dynamic electrochemical monitoring.The approach enabled a systematic analysis of how the geometric characteristics of a curved surface and variations in cathode area jointly influence local corrosion dynamics.A series of flat and curved(curvature radius:3 mm)Cu WBE models,along with cathode areas of varying diameters(φ0.3–0.9 mm),were constructed.By coupling these with in situ current distribution mapping,electrochemical impedance spectroscopy,and polarization curve analysis,it was revealed that the curved surface geometry significantly enhanced chloride ions/proton mass transport and facilitated the dynamic breakdown of passive films,thereby elevating the local corrosion intensity index to 2.9 times that observed under flat-surface conditions.Further investigations demonstrated that a moderate cathode size(φ0.7 mm diameter)effectively optimized the interfacial microenvironment,markedly suppressed the anodic dissolution rate(total current density reduced by 28%).And it increased the breakdown potential of the stainless steel passivation film,enhanced the self-repairing ability of the passivation film.This study,for the first time,elucidates the dynamic mechanisms underlying the synergistic regulation of galvanic current distribution by surface curvature and cathode area,offering critical theoretical insights for the corrosion-resistant design and life prediction of dissimilar metal joints with complex geometries in aggressive environments.展开更多
文摘Radio frequency capacitively coupled plasma source(RF-CCP)with a hollow electrode can increase the electron density through the hollow cathode effect(HCE),which offers a method to modify the spatial profiles of the plasma density.In this work,the variations of the HCE in one RF period are investigated by using a two-dimensional particle-in-cell/Monte-Carlo collision(PIC/MCC)model.The results show that the sheath electric field,the sheath potential drop,the sheath thickness,the radial plasma bulk width,the electron energy distribution function(EEDF),and the average electron energy in the cavity vary in one RF period.During the hollow electrode sheath's expansion phase,the secondary electron heating and sheath oscillation heating in the cavity are gradually enhanced,and the frequency of the electron pendular motion in the cavity gradually increases,hence the HCE is gradually enhanced.However,during the hollow electrode sheath's collapse phase,the secondary electron heating is gradually attenuated.In addition,when interacting with the gradually collapsed hollow electrode sheaths,high-energy plasma bulk electrons in the cavity will lose some energy.Furthermore,the frequency of the electron pendular motion in the cavity gradually decreases.Therefore,during the hollow electrode sheath's collapse phase,the HCE is gradually attenuated.
基金The project supported by the National Nature Science Foundation of China(No.10035020)
文摘Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the dynamic range of operation voltage, repetition frequencies and lifetime of switch. The unique feature of pseudospark switch is its hollow cathode geometry. The hollow cathode effect produced by the hollow cathode provides the protection of the switch for the triggering unit from erosion by high discharge plasma. In this paper, a zinc oxide (ZnO) surface flashover triggering is presented. This trigger unit possesses an excellent time delay (80 ns - 360 ns) and jitter (20 ns - 50 ns) at the switch voltage of 30 kV - 2 kV. The emitted plasma electron density is high enough to trigger switch reliably down to switch voltage of 440 V.
基金the Special Funds for the Construction of an Innovative Province of Hunan(2019GK2231).
文摘To investigate the galvanic corrosion behavior of a copper(Cu)-304 stainless steel curved surface coupling system in a chloride-containing acidic environment,wire beam electrode(WBE)technology was innovatively integrated with dynamic electrochemical monitoring.The approach enabled a systematic analysis of how the geometric characteristics of a curved surface and variations in cathode area jointly influence local corrosion dynamics.A series of flat and curved(curvature radius:3 mm)Cu WBE models,along with cathode areas of varying diameters(φ0.3–0.9 mm),were constructed.By coupling these with in situ current distribution mapping,electrochemical impedance spectroscopy,and polarization curve analysis,it was revealed that the curved surface geometry significantly enhanced chloride ions/proton mass transport and facilitated the dynamic breakdown of passive films,thereby elevating the local corrosion intensity index to 2.9 times that observed under flat-surface conditions.Further investigations demonstrated that a moderate cathode size(φ0.7 mm diameter)effectively optimized the interfacial microenvironment,markedly suppressed the anodic dissolution rate(total current density reduced by 28%).And it increased the breakdown potential of the stainless steel passivation film,enhanced the self-repairing ability of the passivation film.This study,for the first time,elucidates the dynamic mechanisms underlying the synergistic regulation of galvanic current distribution by surface curvature and cathode area,offering critical theoretical insights for the corrosion-resistant design and life prediction of dissimilar metal joints with complex geometries in aggressive environments.
