Plasma fluctuations, local partial Saha equilibrium, and the broadening of vacuum-arc ion charge state distributions

Journal Article · Sun Aug 01 04:00:00 EDT 1999 · IEEE Transactions on Plasma Science

DOI:https://doi.org/10.1109/27.782282· OSTI ID:682234

Anders, A ^[1]

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1. Lawrence Berkeley National Lab., CA (United States)

Charge state distributions (CSD`s) of Fe, Co, Zr, Nb, Hf, Ag, Pt, Au ions produced at vacuum arc cathode spots are investigated without often-used averaging procedures. Statistical results are used to evaluate the contribution of fluctuations to the broadening of averaged CSD`s. Calculations of Saha equations in the Debye-Hueckel approximation are often successful in replicating experimental CSD`s even when using the simple model of instantaneous freezing. This allows one to use charge state spectrometry as a plasma diagnostic tool for the dense plasma near the cathode spot. Typically, total heavy particle (atoms and ions) densities and electron temperatures of 10{sup 24}--10{sup 25} m{sup {minus}3} and 3--4 eV have been measured this way at the transition zone from equilibrium to nonequilibrium, the event horizon. It was also found that CSD`s for some elements such as Co, Ag, and Hf could not be accurately simulated with the assumption of instantaneous freezing. Here, a more gradual transition to nonequilibrium occurs. This transition can be described by the model of partial local Saha equilibrium. Finally, an axial magnetic field was found to soften the transition to nonequilibrium thus causing broadening of experimental CSD`s.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 682234
• Report Number(s): CONF-980818--
• Journal Information: IEEE Transactions on Plasma Science, Journal Name: IEEE Transactions on Plasma Science Journal Issue: 4 Vol. 27; ISSN ITPSBD; ISSN 0093-3813
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CATHODES
CHARGE STATES
ELECTRIC ARCS
IONIC COMPOSITION
MULTICHARGED IONS
PLASMA DIAGNOSTICS
PLASMA PRODUCTION
PLASMA SIMULATION
SAHA EQUATION