A Multicomponent Theory of the Cathodic Plasma Jet in Vacuum Arcs

Wieckert, Christian

doi:10.1002/ctpp.19870270502

Cited by 71 publications

(45 citation statements)

References 21 publications

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“…Ref. [9][10][11][12][13][14], which indicate an acceleration zone of less than 1 mm. The assumption will be checked and discussed in section IV of this work.…”

Section: Theorymentioning

confidence: 99%

Ion energy distribution functions of vacuum arc plasmas

Byon

Anders

2003

Journal of Applied Physics

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The velocity distribution function of vacuum arc ions can be measured by a time-of-flight technique similar to a method originally proposed by Yushkov. The measuring principle makes use of the welljustified assumption that the ion drift velocity from the cathode spot region to a collector is approximately constant. It is shown that the negative time derivative of the collector current is directly proportional to the ion distribution function provided that the time-averaged source intensity (i.e., emission of ions from cathode spots) is constant until the arc is rapidly switched off. In the experiment, arc termination took about 700 ns, which is much faster than the decay of the ion current measured at the collector placed in more than 2 meters distance from the cathode. The experimental distribution functions for most cathode materials show one large peak with a tail and one or more small peaks at higher ion velocities. The distribution functions for some other materials exhibit several peaks. No conclusive answer can be given about the nature of these peaks. Arguments are presented that the peaks are not caused by different charge states or plasma contamination but rather due to insufficiently averaged source fluctuations and/or acceleration by plasma instabilties.a Author to whom correspondence should be addressed; electronic mail: aanders@lbl.gov 2

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“…Ref. [9][10][11][12][13][14], which indicate an acceleration zone of less than 1 mm. The assumption will be checked and discussed in section IV of this work.…”

Section: Theorymentioning

confidence: 99%

Ion energy distribution functions of vacuum arc plasmas

Byon

Anders

2003

Journal of Applied Physics

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“…In contrast to previous measurements where the ion extraction feature of the system was used, the ion current modulation was detected by a Langmuir probe working in the ion saturation regime with a constant negative bias of -60 V. Because ion acceleration occurs in the vicinity (< 1 mm) of the cathode spot 22,23 , the ion velocity can be treated as constant for the length of the drift region between the cathode and the sheath edge of the detecting probe (s=277 mm in most experiments). The ion velocity is simply…”

Section: Measurment Principle and Experimental Detailsmentioning

confidence: 99%

“…Ref. 2,5,10,22,23,25,28,29 . Here we limit ourselves to one-dimensional, spherical hydrodynamic models because they provide simple physical interpretation and formulas that agree surprisingly well with experimental data.…”

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confidence: 99%

Ion flux from vacuum arc cathode spots in the absence and presence of a magnetic field

Anders

Yushkov

2002

Journal of Applied Physics

344

155

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Because plasma production at vacuum cathode spots is approximately proportional to the arc current, arc current modulation can be used to generate ion current modulation that can be detected far from the spot using a negatively biased ion collector. The drift time to the ion detector can used to determine kinetic ion energies. A very wide range of cathode materials have been used. It has been found that the kinetic ion energy is higher at the beginning of each discharge and approximately constant after 150 µs. The kinetic energy is correlated with the arc voltage and the cohesive energy of the cathode material. The ion erosion rate has in inverse relation to the cohesive energy, enhancing the effect that the power input per plasma particle correlates with the cohesive energy of the cathode material. The influence of three magnetic field configurations on the kinetic energy has been investigated. Generally, a magnetic field increases the plasma impedance, arc burning voltage, and kinetic ion energy. However, if the plasma is produced in a region of low field strength and streaming into a region of higher field strength, the velocity may decrease due to the mirror effect. A magnetic field can increase the plasma temperature but may reduce the density gradients by preventing free expansion into vacuum. Therefore, depending on the configuration, a magnetic field may increase or decrease the kinetic energy of ions. Additionally, the angular distribution of the ion flux and ion kinetic energy has been investigated in the absence of an external magnetic field. The result can be fitted by a superposition of an isotropic and a cosine distribution. * Corresponding Author, aanders@lbl.gov 3

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“…Little recent work has been done on extending PH theories, probably because accumulating evidence indicates that the maximum possible potential humps are only a few volts (5-9 V [6,39]), so while a potential hump may make a significant contribution to the ion energy, it probably is not be the major source of energy for the ions.…”

Section: Theoretical Explanations Of Cathode Ion Parametersmentioning

confidence: 99%

Ion Flux from the Cathode Region of a Vacuum Arc

Miller

Kutzner

1991

Contrib. Plasma Phys.

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This paper reviews the properties of the cathode ion flux generated in the vacuum arc. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cnthode region a t moderate nrc currents are described. An appreciable ion flux (M 10% of total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, though some ion flux may be seen even at angles below the plane of the cnthode surface. The observed spntinl distribution of the ion flux is expressed quite well ns an exponential function of solid angle. The ion f l i m is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply-charged ions. The average ion potcntinl and ion multiplicity increiise significantly for cathode materials with higher arc voltages, but decrease with increasing arc current for a particular material.The main theories concerning ion acceleration in cathode spots are the potcntinl hump theory (PH), which assumes that all ions are creatcd at the same potential, and the gas dynirmic thcory (GD), which assumes that all ions are created with the same flow velocity. Experimental data on the potentials and energies of individual ions indicates that these theories in their original forms are not quite correct, howevcr extensions or modifications of the PH and CD theories seem vcry likely t o be able to predict correct vnlues for the chnrge states, potentials, and energies of individual ions. 1*= 2x(icos el).

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A Multicomponent Theory of the Cathodic Plasma Jet in Vacuum Arcs

Cited by 71 publications

References 21 publications

Ion energy distribution functions of vacuum arc plasmas

Ion energy distribution functions of vacuum arc plasmas

Ion flux from vacuum arc cathode spots in the absence and presence of a magnetic field

Ion Flux from the Cathode Region of a Vacuum Arc

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