Correlation between cathode properties, burning voltage, and plasma parameters of vacuum arcs

Anders, André; Yotsombat, B.; Binder, Róbert

doi:10.1063/1.1371276

Cited by 93 publications

(47 citation statements)

References 15 publications

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“…One has to be aware that these voltages are slightly larger than the actual arc voltage, because of the voltage drop inside the cathode and other relevant parts of the circuit. This offset can be several volts [29]. The general current and voltage pulse shapes are displayed in figure 3(a) for the Nb cathode.…”

Section: Arc Current and Voltagementioning

confidence: 99%

“…Sample mean of voltages and currents (V arc and I arc ), a lower limit for their standard errors (SE), and sample counts (n) measured at the cathode feed through for the time interval: τ=[300, 500] μs. These values are listed for the measurements at each cathode composition and the single-element cathodes are compared to literature data ( * V arc , * I arc ) from [29]. MEA orifice; the times shown are times after triggering, regardless of ion charge or element.…”

Section: Ion Velocity Distributionsmentioning

confidence: 99%

“…The standard error shown in table 3 assumes independent samples and can therefore only act as a lower limit. A comparison to literature data [29] is added to the table, which shows the voltage ( * V arc ) and current ( * I arc ) of 250 μs arc pulses from Nb and Al cathodes, averaged over 16 pulses in the time interval from 150 to 250 μs and additionally corrected by the voltage drop in the circuit. It should be noted that different currents in that magnitude have only a slight influence on arc voltage [30].…”

Section: Arc Current and Voltagementioning

confidence: 99%

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Time-resolved ion energy and charge state distributions in pulsed cathodic arc plasmas of Nb−Al cathodes in high vacuum

Zöhrer

Anders

Franz

2018

Plasma Sources Sci. Technol.

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Cathodic arcs have been utilized in various applications including the deposition of thin films and coatings, ion implantation, and high current switching. Despite substantial progress in recent decades, the physical mechanisms responsible for the observed plasma properties are still a matter of dispute, particularly for multi-element cathodes, which can play an essential role in applications. The analysis of plasma properties is complicated by the generally occurring neutral background of metal atoms, which perturbs initial ion properties. By using a time-resolved method in combination with pulsed arcs and a comprehensive Nb−Al cathode model system, we investigate the influence of cathode composition on the plasma, while making the influence of neutrals visible for the observed time frame. The results visualize ion detections of 600 μs plasma pulses, extracted 0.27 m from the cathode, resolved in mass-per-charge, energy-per-charge and time. Ion properties are found to be strongly dependent on the cathode material in a way that cannot be deduced by simple linear extrapolation. Subsequently, current hypotheses in cathodic arc physics applying to multi-element cathodes, like the so-called 'velocity rule' or the 'cohesive energy rule', are tested for early and late stages of the pulse. Apart from their fundamental character, the findings could be useful in optimizing or designing plasma properties for applications, by actively utilizing effects on ion distributions caused by composite cathode materials and charge exchange with neutrals.

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Section: Arc Current and Voltagementioning

confidence: 99%

Section: Ion Velocity Distributionsmentioning

confidence: 99%

Section: Arc Current and Voltagementioning

confidence: 99%

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Time-resolved ion energy and charge state distributions in pulsed cathodic arc plasmas of Nb−Al cathodes in high vacuum

Zöhrer

Anders

Franz

2018

Plasma Sources Sci. Technol.

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“…For example, one can find data on average ion charge states 10,19 , average burning voltages 20,21 , average ion velocities 15 , or average ion velocity distribution functions 22 .…”

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confidence: 99%

Cathodic arcs: Fractal voltage and cohesive energy rule

Anders

Окс

Yushkov

2005

Applied Physics Letters

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The noise of the burning voltage of cathodic arcs in vacuum was analyzed for a range of cathode materials (C, Mg, Ti, V, Ni, Cu, Zr, Nb, Ag, Hf, Ta, W, Pt, Bi, and Si). Cathodic arcs were generated in a coaxial plasma source, and the voltage noise was measured with a broadband (250 MHz) measuring system. Each measurement of 50,000 points was analyzed by Fast Fourier Transform, revealing a power spectrum ~ 1/f 2 for all metals over several orders of magnitude of frequency f (brown noise). The absence of any characteristic time down to possible cutoffs at high frequencies supports a fractal model of cathode spots. Our preliminary research indicate that materials of high cohesive energy have a cutoff of self-similarity at 50 MHz while no cutoff could be found up to 100 MHz for non-refractory metals. The amplitude of colored noise scaled approximately linearly with the cathode's cohesive energy, which is another manifestation of the Cohesive Energy Rule. a) electronic address: aanders@lbl.gov LBNL-57025 1The plasma of cathodic vacuum arcs is produced at non-stationary cathode spots 1 . Much research, both theoretically 2-7 and experimentally [8][9][10][11][12][13][14] , has been done for decades to understand the spot phenomena that produce non-equilibrium plasmas containing multiply ion charge states. The plasma is mesosonic 15 ,i.e., subsonic for electrons and supersonic for ions, with respect to the local ion sound velocity. Difficulties in experimentation and modeling are associated with the spots' fast changes, small sizes, and extreme gradients of power density and particle densities. The formation of spot plasma is often described as a sequence of microexplosions, where cathode material transitions through various phases, from solid to liquid, non-ideal plasma and/or gas phases, finally turning into in a non-equilibrium, expanding, fully ion ionized plasma 6,16 .With improvement of experimental techniques, faster and smaller phenomena have been discovered. This becomes especially striking when the issue of current density is considered. As the apparent area of electron emission was found to be smaller than previously thought, the corresponding current density increased accordingly 17,18 . There were arguments what constitutes an electron-emitting site.In one extreme, electron emission should occur from areas much larger than the molten crater due to intense ion bombardment of the crater vicinity. On the other hand, the most relevant electron emission area might be smaller than the later visible crater because crater formation could be the result of the action of several spot fragments or cells.In order to make any useful statements on cathode processes and parameters of cathodic arc plasma, many researches decided to repeat measurements and average the measured data. For example, one can find data on average ion charge states 10,19 , average burning voltages 20,21 , average ion velocities 15 , or average ion velocity distribution functions 22 .All parameters fluctuate with large amplitude; in some cases up to...

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“…For example, one can find data on average ion charge states [2,3], average burning voltages [14,15], average velocities [11], or average velocity distribution functions [16]. The arc plasma is known to be "noisy," that is, all parameters fluctuate with large amplitude (some up to 100% of the average value), which can be associated with the explosive nature of cathode spot ignition and plasma production [17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Ion charge state fluctuations in vacuum arcs

Anders¹,

Fukuda²,

Yushkov³

2005

J. Phys. D: Appl. Phys.

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Abstract. Ion charge state distributions of cathodic vacuum arcs have been investigated using a modified time-of-flight method. Experiments have been done in double gate and burst gate mode, allowing us to study both systematic and stochastic changes of ion charge state distributions with a time resolution down to 100 ns. In the double gate method, two ion charge spectra are recorded with a well-defined time between measurements. The elements Mg, Bi, and Cu were selected for tests, representing metals of very different properties. For all elements it was found that large stochastic changes occur even at the limit of resolution. This is in agreement with fast changing arc properties observed elsewhere. Correlation of results for short times between measurements was found but it is argued that this is due to velocity mixing rather than due to cathode processes. The burst mode of time-of-flight measurements revealed the systematic time evolution of ion charge states within a single arc discharge, as opposed to previous measurements that relied on data averaged over many pulses. The technique shows the decay of the mean ion charge state as well as the level of material-dependent fluctuations.

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Correlation between cathode properties, burning voltage, and plasma parameters of vacuum arcs

Cited by 93 publications

References 15 publications

Time-resolved ion energy and charge state distributions in pulsed cathodic arc plasmas of Nb−Al cathodes in high vacuum

Time-resolved ion energy and charge state distributions in pulsed cathodic arc plasmas of Nb−Al cathodes in high vacuum

Cathodic arcs: Fractal voltage and cohesive energy rule

Ion charge state fluctuations in vacuum arcs

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