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Investigation Of Triangular Aperture Grid For Plasma Switch Devices
Abstract
First Page of the Article
Tacitrons are triode gas-discharge tubes, similar in construction
to thyratrons. The primary functional difference between a tacitron and
a thyratron is that the tacitron is designed to be completely
grid-controlled, whereas a thyratron has grid control only over
ignition. Demountable cesium-barium (Cs-Ba) tacitrons have exhibited
very low forward voltage drops in the range of a few volts, hold-off
voltages greater than 200 V, and average conduction current densities
greater than 10 A/cm2. These characteristics yield an average
power switching density on the order of 103 W/cm2
approaching 95% peak switching efficiency. This parameter regime places
the Cs-Ba tacitron in the range of conventional solid-state devices,
with the advantage that the tacitron should reliably operate in extremes
of temperature and radiation. The sealed prototype Cs-Ba tacitron
discussed is intended to demonstrate “off-the-shelf”
operation, taking the first step in moving the tacitron from a
laboratory device to the performance level of a commercial product v
A tacitron is a gas-discharge triode that is designed to be completely grid-controlled. Demountable cesium-barium (Cs-Ba) tacitrons have exhibited very low forward voltage drops in the range of a few volts, hold-off voltages greater than 200 V, and average conduction current densities greater than 10 A/cm2. These characteristics yield an average power switching density on the order of 103 W/cm2 in excess of 95% peak switching efficiency. This parameter regime places the Cs-Ba tacitron in the range of conventional solid-state devices, with the advantage that the tacitron should reliably operate in extremes of temperature and radiation. The intent of this investigation is to determine the feasibility of constructing a 6 kW continuous power inverter unit with a pair of high-current tacitrons
Tacitrons are triode gas-discharge tubes, similar in construction
to thyratrons. The primary functional difference between a tacitron and
a thyratron is that the tacitron is designed to be completely
grid-controlled, whereas a thyratron has grid control only over
ignition. Demountable cesium-barium (Cs-Ba) tacitrons have exhibited
very low forward voltage drops in the range of a few volts, hold-off
voltages greater than 200 V, and average conduction current densities
greater than 10 A/cm2. These characteristics yield an average
power switching density in the order of 103 W/cm2
approaching 95% peak switching efficiency. This parameter regime places
the Cs-Ba tacitron in the range of conventional solid-state devices,
with the advantage that the tacitron should reliably operate in extremes
of temperature and radiation. The high-current tacitron has been
designed to modulate average currents in the range of 100 to 200 A, with
the intent of demonstrating continuous power conditioning capability in
the kilowatt range
The Cs-Ba tacitron is being considered as a switch, or as an
inverter consisting of two switches operating in a push-pull mode, for
power conditioning of low voltage/high current dc power sources
operating in high radiation/high temperature environment, beyond the
limits of semiconductor switches. This paper presents new experimental
results delineating the effect of the various operating parameters on
the grid potential needed for ignition, Vg+, and
extinguishing, Vg-, during stable current
modulation of a planar Cs-Ba tacitron. Parameters investigated are Cs
pressure, emitter temperature, TE, discharge current, I<sub>C
</sub>, and modulation frequency, fg. The value of V<sub>g
</sub>+, which is independent of TE, decreases as
Cs pressure increases, but increases as either IC or f<sub>g
</sub> increases. Increasing the emitter temperature from
1100-1200°C only slightly decreases the forward voltage drop in the
device by ~0.2 V. The value of |Vg-| increases
with Cs pressure, decreases with increased TE, and is
sensitive to changes in fg. At IC=5 A, the value of |V<sub>g
</sub>-| for stable modulation shows a maximum between 8 kHz
and 10 kHz. The Cs pressure, IC, fg, and Vg<sup>+
</sup> all affect the ignition delay time; depending on the operating
conditions, it increases from 5-30 μs to an equilibrium value of
10-45 μs during the first 2 ms in the pulse train
1. Introduction.- 2. Single-Particle Motions.- 3. Plasmas as Fluids.- 4. Waves in Plasmas.- 5. Diffusion and Resistivity.- 6. Equilibrium and Stability.- 7. Kinetic Theory.- 8. Nonlinear Effects.- Appendices.- Appendix A. Units, Constants and Formulas, Vector Relations.- Appendix B. Theory of Waves in a Cold Uniform Plasma.- Appendix C. Sample Three-Hour Final Exam.- Appendix D. Answers to Some Problems.- Index to Problems.
The operation characteristics of the Cs‐Ba tacitron as a switch are investigated experimentally in three modes: (a) breakdown mode; (b) I‐V mode; and (c) current modulation mode. The switching frequency, grid potentials for ignition and extinguishing of discharge, and the Cs pressure and emission conditions (Ba pressure and emitter temperature) for stable current modulation are determined. The experimental data is also used to determine the off time required for successful ignition, and the effects of the aforementioned operation parameters on the ignition duty cycle threshold for stable modulation. Operation parameters measured include switching frequency up to 8 kHz, hold‐off voltage up to 180 V, current densities in excess of 15 A/cm2, switch power density of 1 kW/cm2, and a switching efficiency in excess of 90% at collector voltages greater than 30 V. The voltage drop strongly depends on the Cs pressure and to a lesser extent on the emission conditions. Increasing the Cs pressure and/or the emission current lowers the voltage drop, however, for the same initial Cs pressure and emission conditions, the voltage drop in the I‐V mode is usually lower than that during current modulation. As long as the discharge current is kept lower than the emission current, the voltage drop during stable current modulation could be as low as 3 V.
Sov. Phys. Tech. Phys.
- V Z Kaibyshev
- G A Kuzin
- M V Mel 'nikov
- Sov