Analysis of Anode Current From a Thermionic Cathode With a 2-D Work Function Distribution

Jassem, Abhijit; Chernin, D.; Petillo, John; Lau, Y. Y.; Jensen, Aaron; Ovtchinnikov, Serguei

doi:10.1109/tps.2020.3048097

Cited by 23 publications

(10 citation statements)

References 14 publications

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“…In our nonuniform emission model, even though electrons are restricted along the cathode-anode direction with no lateral momentum, our model is able to predict the trend of the change in the emission nonuniformity as temperature changes. Such a trend has also been observed in experiments [60,61] and is consistent with some previous computational studies [39,40,47,48].…”

Section: Two-dimensional Emission Mapsupporting

confidence: 92%

“…The smooth TL-FSCL transition in the predicted curves arises as a natural consequence of the nonuniform emission from the polycrystalline cathode with a nonuniform spatial distribution of work function. Previous studies [39,40,47,48] show that the 3-D space charge effect plays a significant role in making the transition region smooth for a nonuniform cathode. However, when using a work function map for a real cathode derived from DFT and EBSD, a model only considering the 3-D space charge effect predicts a TL-FSCL transition in a Miram curve sharper than experimental results.…”

Section: Emitted Current Densitymentioning

confidence: 95%

“…The theory of the anomalous Schottky effect [46] studied the contribution of the patch field effect (electrostatic potential nonuniformity on the cathode surface based on local work function values) and the Schottky barrier lowering effect on the smoothness of the TL-FSCL transition in J − V curves. Studies on space charge effects [39,40,47,48] reveal the contribution of 3-D space charge fields on the smooth transition in J − T curves. However, the TL-FSCL transition behaviors predicted from these two separate sets of studies are sharper than experimental observations, indicating that some physical effects are missing.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

Chen¹,

Jacobs²,

Petillo³

et al. 2021

Preprint

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A new physics-based model is developed that predicts the emitted current from thermionic emission that accurately spans from the temperature-limited (TL) to the full-space-charge-limited (FSCL) regions. Experimental observations of thermionic electron emission demonstrate a smooth transition between TL and FSCL regions of the emitted-current-density-versus-temperature (J − T ) (Miram) curve and the emitted-current-density-versus-voltage (J − V ) curve. Knowledge of the temperature and shape of the TL-FSCL transition is important in evaluating the thermionic electron emission performance of cathodes, including predicting the lifetime. However, there have been no firstprinciples physics-based models that can predict the smooth TL-FSCL transition region for real thermionic cathodes without applying physically difficult to justify a priori assumptions or empirical phenomenological equations. Previous work detailing the nonuniform thermionic emission found that the effects of 3-D space charge, patch fields (electrostatic potential nonuniformity on the cathode surface based on local work function values), and Schottky barrier lowering can lead to a smooth TL-FSCL transition region from a model thermionic cathode surface with a checkerboard spatial distribution of work function values. In this work, we construct a physics-based nonuniform emission model for commercial dispenser cathodes for the first time. This emission model is obtained by incorporating the cathode surface grain orientation via electron backscatter diffraction (EBSD) and the facet-orientation-specific work function values from density functional theory (DFT) calculations. The model enables construction of two-dimensional emitted current density maps of the cathode surface and corresponding J − T and J − V curves. The predicted emission curves show excellent agreement with experiment, not only in TL and FSCL regions but, crucially, also in the TL-FSCL transition region. This model provides a method to predict the thermionic emission from the microstructure of a commercial cathode, and improves the understanding on the relationship between thermionic emission and cathode microstructure, which is beneficial to the design of vacuum electronic devices.

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Section: Two-dimensional Emission Mapsupporting

confidence: 92%

Section: Emitted Current Densitymentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

Chen¹,

Jacobs²,

Petillo³

et al. 2021

Preprint

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show abstract

“…This article is a significant extension of the plenary paper [75] given at the 2020 IEEE International Conference on Plasma Science. Various topics presented in [75] were published in [76]- [79], [67], [68].…”

Section: Acknowledgmentmentioning

confidence: 99%

Explicit Brillouin Flow Solutions in Magnetrons, Magnetically Insulated Line Oscillators, and Radial Magnetically Insulated Transmission Lines

Lau

Packard

Swenson

et al. 2021

IEEE Trans. Plasma Sci.

Self Cite

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This article re-examines the Brillouin flow solutions in crossed-field diodes, with applications to magnetrons, magnetically insulated line oscillators (MILOs), and magnetically insulated transmission lines (MITLs). The Brillouin flow solutions are constructed for various geometries, including planar magnetrons, MILOs, and MITLs, cylindrical magnetrons with electrons flowing in the azimuthal direction, cylindrical MITLs and MILOs with electrons flowing in the axial direction, and radial MITLs and MILOs with electrons flowing in the radial direction. A common theme of this analysis is that two main external parameters are used to characterize the Brillouin flow: the anode-cathode voltage (V a ) and the total magnetic flux within the crossed-field diodes ( A a ). These two parameters are equivalent to the gap voltage and a specification of the degree of magnetic insulation, which is approximately equal to the ratio of the magnetic field to the Hull cutoff (HC) magnetic field.The magnetic flux may be provided externally by a magnet (as in a magnetron) or by the wall currents without an external magnet (as in a MILO or MITL), or by some combination of the two, as in the intermediate case of a magnetron-MILO hybrid. Once these two parameters are specified, the electron flow speed at the top of the Brillouin hub is uniquely determined. This immediately yields the Buneman-Hartree (BH) condition according to the Brillouin flow model, whether it be a planar magnetron or a cylindrical MILO. In so doing, we have obtained, for the first time using the Brillouin flow model, the BH condition for a cylindrical MILO, and we show that the same condition is obtained from the single-particle orbit model. We also found that, in general, the electron current within the Brillouin hub Manuscript

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“…Despite a considerable effort done to explain the shape of the Miram curves [6][7][8][13][14][15][16][17][18], the physical processes governing the thermal emission have not been fully understood yet. Recently, significant advancement has been made in understanding the processes responsible for the softening of the knee has due to the works of Chernin et al [7] and Jassem et al [18].…”

Section: Introductionmentioning

confidence: 99%

Edge effect on the current-temperature characteristic of thermionic cathodes

Sitek,

Torfason,

Manolescu

et al. 2021

Preprint

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We perform a computational study, based on the molecular dynamics method, of the shape of Miram curves obtained from microscale planar diodes. We discuss the smooth transition from the source-limited to space-charge-limited regime due to the finite size of the emitter, i.e. the "knee" in the Miram curve. In our model we find that the smoothing occurs mostly due to the increased emission at the external edges of the emitting area, and that the knee becomes softer when the size of the emitting area decreases. We relate this to the recent work which has described how a heterogeneous work function similarly affects the Miram curve.

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Analysis of Anode Current From a Thermionic Cathode With a 2-D Work Function Distribution

Cited by 23 publications

References 14 publications

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

Explicit Brillouin Flow Solutions in Magnetrons, Magnetically Insulated Line Oscillators, and Radial Magnetically Insulated Transmission Lines

Edge effect on the current-temperature characteristic of thermionic cathodes

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