Structure and time behavior of vacuum arc cathode spots

Barengolts, S. A.; Mesyats, G. A.; Shmelev, D. L.

doi:10.1109/tps.2003.818449

Cited by 60 publications

(36 citation statements)

References 23 publications

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“…According to the ecton model [41][42][43][44], thermal runaway occurs on microprotrusions until they explode with a delay time associated with the material-specific action. The ecton is the "quantum" of an electron emission event or microexplosion.…”

Section: Fractal Cathode Spotsmentioning

confidence: 99%

The evolution of ion charge states in cathodic vacuum arc plasmas: a review

Anders¹

2012

Plasma Sources Sci. Technol.

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ACKNOWLEDGMENTMany of the here-collected results are based on ideas and contributions by close friends and colleagues. Running the risk of offending those not mentioned, I gratefully acknowledge the input over the years from just a few: B. Jüttner, E. Hantzsche, P. Siemroth, T. Schülke, I. Brown, E. Oks and G. Yushkov. This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. DISCLAIMERThis document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California. 2The evolution of ion charge states in cathodic vacuum arc plasmas: a review André AndersLawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 53, Berkeley, California 94720, USA Email: aanders@lbl.gov AbstractCathodic vacuum arc plasmas are known to contain multiply charged ions. 20 years after "Pressure Ionization: its role in metal vapour vacuum arc plasmas and ion sources" appeared in vol. 1 of Plasma Sources Science and Technology, it is a great opportunity to re-visit the issue of pressure ionization, a non-ideal plasma effect, and put it in perspective to the many other factors that influence observable charge state distributions, such as the role of the cathode material, the path in the density-temperature phase diagram, the "noise" in vacuum arc plasma as described by a fractal model approach, the effects of external magnetic fields and charge exchange collisions with neutrals. A much more complex image of the vacuum arc plasma emerges putting decades of experimentation and modeling in perspective.

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Section: Fractal Cathode Spotsmentioning

confidence: 99%

The evolution of ion charge states in cathodic vacuum arc plasmas: a review

Anders¹

2012

Plasma Sources Sci. Technol.

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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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“…In ref. [20], the arc voltage jump was observed before the jump; in the present situation, it was difficult to increase the arcing voltage, because the voltage was determined between the plasma and cathode. It is likely that the surrounding high density plasma and the high temperature electron emitting cathode supported the jumping of arcing.…”

Section: Initiation Of Unipolar Arcingmentioning

confidence: 69%

“…In the unipolar arc trail observed in LHD, the arc spot could not jump a narrow scratch on the nanostructured tungsten [19]. In vacuum arc, sometimes the jumping phenomena was observed [20]. In ref.…”

Section: Initiation Of Unipolar Arcingmentioning

confidence: 95%

Superimposition of Pulses to Steady Arc Discharge in Toroidal Divertor Simulator

Kajita

Uchiyama

Ohno

2012

Plasma and Fusion Research

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A pulsed discharge was superimposed to a steady state arc discharge in the toroidal divertor simulator NAGDIS-T. The dynamic response of the plasma was observed with an electrostatic probe and fast framing camera. In the first loop plasma, which is close to the plasma source, the density becomes higher in response to the pulsed discharge, and the emission from the plasma significantly increases. On the other hand, in the second loop plasma, where a recombining plasma is formed, the emission from the plasma disappears in response to the pulse. Just after the pulsed discharge, plasma instabilities were formed and they were propagated from the upstream to downstream at the velocity of ∼10 km/s. After the series of pulsed plasma experiments, arc trails were recorded around the cathode area. On a molybdenum cover of the cathode, unipolar arcing was initiated on the surface. It is likely that the pulsed discharge leads to instabilities and initiate the unipolar arcing consequently.

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Structure and time behavior of vacuum arc cathode spots

Cited by 60 publications

References 23 publications

The evolution of ion charge states in cathodic vacuum arc plasmas: a review

The evolution of ion charge states in cathodic vacuum arc plasmas: a review

Cathodic arcs: Fractal voltage and cohesive energy rule

Superimposition of Pulses to Steady Arc Discharge in Toroidal Divertor Simulator

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