Formation time and heating mechanism of arc cathode craters in vacuum

Jüttner, B.

doi:10.1088/0022-3727/14/7/014

Cited by 86 publications

(26 citation statements)

References 12 publications

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“…It is clear that physical cutoffs exist but the (rather elusive) characteristic elementary size and times have not been confirmed despite numerous sophisticated investigations 13,35,36 . Since the early work by Kesaev 9 , the existence of spot cells or fragments was confirmed by high-resolution diagnostics 13,37 , though the lower scaling cutoff would only be confirmed if higher resolution techniques did not find smaller structures and faster changes.…”

Section: Lbnl-57025mentioning

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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Section: Lbnl-57025mentioning

confidence: 99%

Cathodic arcs: Fractal voltage and cohesive energy rule

Anders

Окс

Yushkov

2005

Applied Physics Letters

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“…This is an indication that fundamental processes of plasma production at cathode spots have features whose characteristic time is shorter than 150 ns. This is not surprising because fast changes and fluctuations have previously been observed in other arc parameters, such as crater formation [34,35], voltage and light emission [20] and absorption [36]. figure 14 for Mg. Due to the non-zero width of the velocity distribution, the information on cathode processes is smeared out and mixed, and thus the extracted ion current becomes correlated over a time determined by the width of the velocity distribution function.…”

Section: Discussionmentioning

confidence: 56%

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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“…spot brightness and burning voltage 111, 121. The crater formation time as a characteristic time constant of the spot processes is in the order of only a few nanoseconds [13].…”

Section: Compilation Of Cathode Spot Parametersmentioning

confidence: 99%

Effects of Non‐Ideality and Non‐Equilibrium in the Cathode Spot Plasma of Vacuum Arcs

Anders

1989

Contrib. Plasma Phys.

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The cathode spot plasma of a metal vapour arc in vacuum is non-ideal (electron density no -loz5 -102' m-3, temperature T N 1 -5 eV, plasma parameter r = 0.6-0.1). The fast expansion of the spot plasma into the ambient vacuum leads t o a non-equilibrium charge state distribution ("frozen" state of ionization). The calculations presented show that the freezing of the different charge states appears a t different distances from the spot, therefore a t different plasma densities and temperatures. I n this way, specific proportions of the ion species are produced which do not agree with any equilibrium state. The freezing of the charge states occurs near the cathode spot ( r = 5 -50pm, T -distance from the spot centre) where the plasma is weakly non-ideal (r = 0.2-0.6).

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Formation time and heating mechanism of arc cathode craters in vacuum

Cited by 86 publications

References 12 publications

Cathodic arcs: Fractal voltage and cohesive energy rule

Cathodic arcs: Fractal voltage and cohesive energy rule

Ion charge state fluctuations in vacuum arcs

Effects of Non‐Ideality and Non‐Equilibrium in the Cathode Spot Plasma of Vacuum Arcs

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