Current density limitations in a fast-pulsed high-voltage vacuum diode
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Authors
Welsh, David S.
Subjects
current density
cathode spot
vacuum diode
whisker
unipolar arc
space charge
numerical
simulation
cathode spot
vacuum diode
whisker
unipolar arc
space charge
numerical
simulation
Advisors
Schwirzke, Fred
Date of Issue
1992-06
Date
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
An investigation into the limitations on the enhanced field-emitted current density
in a fast-pulsed (rise-time = ns), high voltage (> 106 V), 1-inch vacuum diode was
conducted using a computer simulation based on the Fowler-Nordheim equation.
Oscillations in the emitted current density (due to the change in the amount of
space charge within the gap) were found to quickly decay into a final steady-state for
the voltages applied. Steady-state values for a wide variety of work functions, electric
field enhancement factors (based on the theory that "whiskers" on the cathode surface
experience varying degrees of enhancement), and applied potentials were compared
to two benchmarks: the amount of current density required to explode a whisker in
< 10 ns by joule heating (J E = 109 A/cm2
); and the Child-Langmuir (C-L) spacecharge-
limited current density. Steady-state values were found to be less than J E . One model of the formation
process of a plasma at the cathode surface requires that J E be met or exceeded by
the steady-state value. Thus, such a model is not supported by this project's findings.
The C-L limit is based on a thermionic-type emission process. As only pure field
emission (i.e., no thermionic emission included) was considered, the steady-state
values were, in all conclusive cases, less than the corresponding C-L limited values.
Type
Thesis
Description
Series/Report No
Department
Physics
Organization
Naval Postgraduate School
Identifiers
NPS Report Number
Sponsors
Funder
Format
56 p.;28 cm.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.