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15 Feb 2012

Volume 111, Issue 4, Articles (04xxxx)

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J. Appl. Phys. 111, 043501 (2012); http://dx.doi.org/10.1063/1.3680881 (8 pages)

Gregory J. McGraw and Stephen R. Forrest
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back to top Plasmas and Electrical Discharges

Investigation of the swirl flow on anode surface in high-current vacuum arcs

Shenli Jia, Dingge Yang, Lijun Wang, and Zongqian Shi

J. Appl. Phys. 111, 043301 (2012); http://dx.doi.org/10.1063/1.3684974 (6 pages)

Online Publication Date: 17 February 2012

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The anode activities are critical for high-current vacuum arc characteristics, especially the interruption performance of vacuum interrupters. The serious anode melting and sputter of liquid droplets into arc column often lead to interruption failure. In our previous work, the obvious anode melting and swirl flow of melted anode metal were detected at the center of anode surface when arc current exceeded a critical value under axial magnetic field (AMF). It is found that the AMF has great influence on the anode swirl flow, no swirl flow is found on the butt plate anode without AMF, but obvious swirl flow can be found when a moderate AMF is applied. Meanwhile, the swirl flow direction reversed if the AMF direction also reversed. The electromagnetic forcej×Bin anode melting pool and the impact force of ions coming from cathode plasma jets which are inclined to the arc axis on anode surface were thought to be two main possible reasons. In order to discover the physics behind the anode swirl flow phenomenon, special experiments have been conducted in this paper. Both the theoretical analysis and experimental results indicate that it is not the electromagnetic force but the interaction between ions from cathode plasma jets and anode melting pool that leads to the observed anode swirl flow. The inclination direction of cathode plasma jets, which is consistent with the direction of magnetic field vector, determines the direction of swirl flow.
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82.45.-h Electrochemistry and electrophoresis
64.70.D- Solid-liquid transitions

Ion current density measurements in a copper vacuum arc with different refractory anode thicknesses

I. I. Beilis, Y. Koulik, and R. L. Boxman

J. Appl. Phys. 111, 043302 (2012); http://dx.doi.org/10.1063/1.3686183 (6 pages)

Online Publication Date: 22 February 2012

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The time-dependent ion current density was measured in a hot refractory anode vacuum arc (HRAVA) sustained between a consumed water-cooled cylindrical Cu cathode and non-consumed cylindrical W anodes with thickness d = 5, 10, 15, 20, or 30 mm separated by an h = 10 mm gap. Arc currents of I = 130, 150, 175, and 200 A were applied for a period of 90 s. Ion current density Ji extracted from the plasma was measured using a probe located at varying distances from the electrode axis. The active surface of the probe was oriented to be either perpendicular or parallel to the radially expanding plasma to measure the directed or random component of Ji, respectively. Ji started at arc ignition and grew slowly, passed through a peak, and reached a final steady state level. This level increased with arc current and decreased with probe distance. The time to reach the steady state decreased when d was decreased from 30 to 5 mm, for I = 200 A from 48 to 12 s and for I = 150 A from 69 to 20 s, and weakly depended on probe orientation. Ji to the perpendicular probe significantly exceeded that for the parallel orientation.
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52.70.Ds Electric and magnetic measurements
52.80.Vp Discharge in vacuum
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Phase locking of high power relativistic backward wave oscillator using priming effect

Yan Teng, Wei Song, Jun Sun, Renzhen Xiao, Zhimin Song, Ligang Zhang, Zhiqiang Zhang, Lijun Zhang, Yuchuan Zhang, Jiawei Li, and Jinyong Fang

J. Appl. Phys. 111, 043303 (2012); http://dx.doi.org/10.1063/1.3686620 (7 pages) | Cited 3 times

Online Publication Date: 23 February 2012

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The phase-locking approach using the priming effect is developed for high power relativistic backward wave oscillators (RBWO). A plasma switch is conceived to avoid the feedback effect. In experiment, multicavity RBWO of 200 MW with the 73 MHz half power bandwidth is phase-locked under the injection power ratio 0.044 for the frequency separation of 20 MHz. We found that it takes more time to reach stable phase-locking than to achieve saturation of RBWO generation. The external signal of higher power results in the longer time duration of phase locking. Besides phase-locking, the priming effect leads to longer microwave pulse duration.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
52.75.Kq Plasma switches (e.g., spark gaps)

Correlation of current drop, filling gas pressure, and ion beam emission in a low energy Mather-type plasma focus device

R. A. Behbahani and F. M. Aghamir

J. Appl. Phys. 111, 043304 (2012); http://dx.doi.org/10.1063/1.3686753 (5 pages) | Cited 1 time

Online Publication Date: 24 February 2012

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The behavior of current drop and its correlation with ion beam emission during the radial phase of a high inductance low energy Mather type plasma focus device have been studied. The study includes two ranges of filling gas pressure, namely the low range of 0.2–0.8 mbar and the high range of 0.8–1.5 mbar. Two different current simulation processes were performed to aid the interpretation of the experimental results. Within the low range of operating pressure, an acceptable match between the computed and experimental current signals was achieved when the effects of anomalous resistances were contemplated. While in the high range of pressure, the computed and experimental current traces were in line even without considering the effects of anomalous resistances. The analysis shows that by decreasing the filling gas pressure the effects of instabilities are intensified. The computed and experimental current traces, along with ion beam signals gathered from a faraday cup, show that there is a strong correlation between the intensity of ion beam and its duration with the current drop during the radial phase.
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52.59.Fn Multistage accelerated heavy-ion beams
52.75.-d Plasma devices
52.25.-b Plasma properties
52.65.-y Plasma simulation
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Real-time observation of the capacitance variation in a surface dielectric layer in radio frequency discharge

Jin-Young Bang, Kyoung Yoo, and Chin-Wook Chung

J. Appl. Phys. 111, 043305 (2012); http://dx.doi.org/10.1063/1.3688052 (5 pages)

Online Publication Date: 27 February 2012

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The capacitance of an Al2O3 layer coated on a probe was measured in real-time in plasma using the harmonic method. The measured capacitance was influenced by the applied power and the exposure time to the plasma. Upon varying the power, the capacitance quickly changed and then slowly saturated. The change in the capacitance was partly understood to be due the temperature dependence of the dielectric constant. However, the rate of the capacitance change as a function of temperature was higher than that typically observed, and the quick response to varying power was too fast to be explained by the temperature variation. These results showed that other effects besides temperature should be considered to explain this phenomenon.
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52.80.Pi High-frequency and RF discharges
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
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