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Title: Production of neutrals and their and effects on the ion chargestates in cathodic vacuum arc plasmas

Abstract

Cathodic arc plasmas are considered fully ionized and theycontain multiply charged ions, yet, gaseous and metal neutrals can bepresent. It is shown that they can cause a significant reduction of theion charge states as measured far from the cathode spots. Several cathodematerials were used to study the evolution the mean ion charge state as afunction of time after arc ignition. The type of cathode material, arccurrent amplitude, intentionally increased background gas, additionalsurfaces placed near the plasma flow, and other factors influence thedegree of charge state reduction because all of these factors influencethe density of neutrals. In all cases, it was found that the mean ioncharge state follows an exponential decay of first order, Q(t) = A *exp(t/tau) + Qss, where A is a parameter describing the importance of thedecay, tau is the characteristic decay time, and Qss is a steady-statevalue approached for continuous arc operation. The extrapolated valuesQ(t-->0) indicate surprisingly high mean charge states as produced atcathode spots and not "skewed" by charge exchange collisions withneutrals.

Authors:
; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE. Administrator for National Nuclear SecurityAdministration Nonproliferation and National Security ProgramDirection
OSTI Identifier:
926618
Report Number(s):
LBNL-63444
R&D Project: Z2N196; BnR: NN4101010
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 102; Related Information: Journal Publication Date: 08/15/2007
Country of Publication:
United States
Language:
English
Subject:
70; cathodic arcs neutrals ion charge states

Citation Formats

Anders, Andre, Oks, Efim M., and Yushkov, Georgy Yu.. Production of neutrals and their and effects on the ion chargestates in cathodic vacuum arc plasmas. United States: N. p., 2007. Web. doi:10.1063/1.2769789.
Anders, Andre, Oks, Efim M., & Yushkov, Georgy Yu.. Production of neutrals and their and effects on the ion chargestates in cathodic vacuum arc plasmas. United States. doi:10.1063/1.2769789.
Anders, Andre, Oks, Efim M., and Yushkov, Georgy Yu.. Wed . "Production of neutrals and their and effects on the ion chargestates in cathodic vacuum arc plasmas". United States. doi:10.1063/1.2769789. https://www.osti.gov/servlets/purl/926618.
@article{osti_926618,
title = {Production of neutrals and their and effects on the ion chargestates in cathodic vacuum arc plasmas},
author = {Anders, Andre and Oks, Efim M. and Yushkov, Georgy Yu.},
abstractNote = {Cathodic arc plasmas are considered fully ionized and theycontain multiply charged ions, yet, gaseous and metal neutrals can bepresent. It is shown that they can cause a significant reduction of theion charge states as measured far from the cathode spots. Several cathodematerials were used to study the evolution the mean ion charge state as afunction of time after arc ignition. The type of cathode material, arccurrent amplitude, intentionally increased background gas, additionalsurfaces placed near the plasma flow, and other factors influence thedegree of charge state reduction because all of these factors influencethe density of neutrals. In all cases, it was found that the mean ioncharge state follows an exponential decay of first order, Q(t) = A *exp(t/tau) + Qss, where A is a parameter describing the importance of thedecay, tau is the characteristic decay time, and Qss is a steady-statevalue approached for continuous arc operation. The extrapolated valuesQ(t-->0) indicate surprisingly high mean charge states as produced atcathode spots and not "skewed" by charge exchange collisions withneutrals.},
doi = {10.1063/1.2769789},
journal = {Journal of Applied Physics},
number = ,
volume = 102,
place = {United States},
year = {Wed May 23 00:00:00 EDT 2007},
month = {Wed May 23 00:00:00 EDT 2007}
}
  • Cathodic arc plasmas are considered fully ionized and they contain multiply charged ions, yet gaseous and metal neutrals can be present. It is shown that they can cause a significant reduction of the ion charge states as measured far from the cathode spots. Several cathode materials were used to study the evolution of the mean ion charge state as a function of time after arc ignition. The type of cathode material, arc current amplitude, intentionally increased background gas, additional surfaces placed near the plasma flow, and other factors influence the degree of charge state reduction because all of these factorsmore » influence the density of neutrals. In all cases, it was found that the mean ion charge state follows an exponential decay of first order, Q(t)=A exp(-t/{tau})+Q{sub ss}, where A is a parameter describing the importance of the decay, {tau} is the characteristic decay time, and Q{sub ss} is a steady-state value approached for continuous arc operation. The extrapolated values Q(t{yields}0) indicate surprisingly high mean charge states as produced at cathode spots and not ''skewed'' by charge exchange collisions with neutrals.« less
  • Cathodic 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 ofmore » 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.« less
  • Time-dependent ion charge state measurements for Pb and Bi cathodic arc plasmas revealed unexpected differences: the mean Bi ion charge state dropped much stronger and with a longer time constant. It is shown that the differences in thermal conductivity and vapor pressure led to much higher neutral density for Bi, which in turn can cause charge exchange collisions. The results have implications beyond Pb and Bi plasmas: most importantly, they imply that the 'true' ion charge states, as emitted from the cathode spots, are higher than what is generally measured and published.
  • Time-dependent ion charge state measurements for Pb and Bicathodic arc plasmas revealed unexpectedly strong differences: the meanBi ion charge state dropped much stronger and with a longer time constantthan the mean Pb ion charge state. It is shown that the difference inthermal conductivity led to much higher vapor pressure for Bi, which inturn much more effectively caused charge exchange collisions. The resultshave implications beyond Pb and Bi plasmas, most importantly that the"true" charge states as emitted from the cathode spot are higher thanwhat is generally measured and published.
  • The effects of pulsing parameters such as the duty cycles, frequencies, and arc currents on the production and distribution of macroparticles (MPs) were studied. A tunable pulsed arc power supply that could provide either direct current (dc) or pulsed current plus dc was used in the experiments. Copper and titanium were used as the cathodes, and glasses were used as the substrate. Optical microscopy, scanning electron microscopy, and special image processing were utilized to investigate the MPs deposited onto the substrate. Our results illustrate the general trend that the MP density increases with higher dc but decreases with increasing pulsingmore » frequency. There is no obvious relationship between the MP density and the duty cycle at high dc but the MP density obviously increases with the duty cycle at low dc.« less