Field emission from metal particles in a vacuum gap

Hurley, R.E.; Parnell, T. M.

doi:10.1088/0022-3727/2/6/313

Cited by 20 publications

(10 citation statements)

References 11 publications

(7 reference statements)

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“…Hence the MP starts to move in the interelectrode space, under vacuum, towards the cathode, driven by the macroscopic electric field. Its initial charge Q MP [47] is controlled by the electrode surface electric field. This charge is expressed as follows:…”

Section: Microparticle Modelmentioning

confidence: 99%

Dynamics of microparticles in vacuum breakdown: Cranberg’s scenario updated by numerical modeling

Seznec

Dessante

Jäger

et al. 2017

Phys. Rev. Accel. Beams

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Microparticles (MP) and thermofield emission in vacuum are mainly caused by the roughness present at the surface of electrodes holding a high voltage. They can act as a trigger for breakdown, especially under high vacuum. This theoretical study discusses the interactions between one MP and the thermofield emission electron current as well as the consequences on the MP's transit. Starting from Cranberg's assumptions, new phenomena have been taken into account such as MP charge variation due to the secondary electron emission induced by energetic electron bombardment. Hence, the present model can be solved only numerically. Four scenarios have been identified based on the results, depending on the electron emission current from the cathode roughness (tip) and the size of the MP released at the anode, namely (i) one way; (ii) back and forth; (iii) oscillation; and (iv) vaporization. A crash study of the MP on the cathode shows that the electron emission can decrease if the MP covers the thermoemissive tip, i.e., if the MP is larger than the tip size-a phenomenon often called "conditioning"-and helping to increase the voltage holding in vacuum without breakdown.

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Section: Microparticle Modelmentioning

confidence: 99%

Dynamics of microparticles in vacuum breakdown: Cranberg’s scenario updated by numerical modeling

Seznec

Dessante

Jäger

et al. 2017

Phys. Rev. Accel. Beams

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“…U c is the critical voltage determined by the complemented Cranberg's hypothesis (7). U b is the instant breakdown voltage.…”

Section: Cranberg's Hypothesis Applied To An Impulse Voltage Breakdowmentioning

confidence: 99%

“…As a result, there have been a number of theories concerning the processes involved when a breakdown of a vacuum gap occurs [1][2][3][4][5][6][7][8][9][10]. Researches on vacuum breakdown have shown that breakdown tended to be field-dependent for a short contact gap d ≤0.5 mm.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of impulse voltage breakdown in high voltage vacuum interrupters with long contact gap

Zhang

Liu

Yang

2014

IEEE Trans. Dielect. Electr. Insul.

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The objective of this paper is to propose a breakdown mechanism of lightning impulse voltage in high voltage vacuum interrupters (VIs) with long contact gap by complementing the Cranberg "clump" hypothesis with an impulse voltage and a non-uniform field. The Cranberg "clump" hypothesis assumed that the vacuum breakdown was due to the loosely adhering microscopic particles under a DC voltage and a uniform field. The microscopic particles might be torn from an electrode surface at a critical voltage. We considered the microscopic particles located at the area with the maximum electric field had the highest possibility to be accelerated. Therefore, the transit process of the micro-particles to the opposing electrodes was under a non-uniform field distribution driven by an impulse voltage. The rise rate of the impulse voltage applied was also considered. As a result, it was found that the breakdown voltage of a vacuum gap depends upon a 0.76 power of the gap length for the plate-to-plate contacts. The diameter of the contacts was 60 mm. The contact radius of curvature was 6 mm. In the same conditions, our previous experimental results showed that the impulse breakdown voltage was in a range of 0.70 to 0.79 power of the contact gap. So the experimental results supported the Cranberg hypothesis in its extension to the impulse breakdown under non-uniform field in high-voltage VIs. Thereafter, this proposed breakdown mechanism is a complement to the Cranberg "clump" hypothesis in terms of impulse voltage breakdown under a non-uniform field in high voltage VIs.Index Terms -breakdown mechanism, impulse voltage, vacuum interrupters, Cranberg hypothesis, microscopic particles, non-uniform field.

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“…Charge may in principle be exchanged between the particle and target either by direct ohmic conduction through the surface films during conthct, or by close-proximity quantum mechanical tunnelling. In the special case where both surfaces are atomically clean, charge exchange would only be limited by the electrical properties of the interacting materials, and would be completed in a time comparable with the relaxation time T of typical metals, where T N 10-19-10-17 s. Since 7 < f C , it follows that the reversed charge acquired by a particle under these circumstances would be the equilibrium value for a sphere in contact with a plane (Hurley and Parnell 1969), which for a vacuum-metal interface would be…”

Section: 2 Electrical Considerationsmentioning

confidence: 99%

“…It is significant to note from these computations that E1 provides the dominant contribution for all values of g, so that Vp(g) z qI/ZCo(g) to a good approximation. It is also important to note from figure 5 that E g c 109 V m-1 for all conditions, so that the possibility of in-flight field emission from the target to the particle (Hurley and Parnell 1969) can be ignored in these experiments.…”

Section: 2 Electrical Considerationsmentioning

confidence: 99%

The influence of surface oxidation on the electron tunnelling mechanism of microparticle charge reversal during a bouncing impact on a charged conductor

Latham

Brah

1977

J. Phys. D: Appl. Phys.

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Carbonyl iron microspheres 0.1-2 pm diameter, with velocities of 10-100 ms-1 and positive charges of (0.5-5)x 10-16C have been used for a comparative study of the charge reversal that occurs during a bouncing impact with negatively charged copper and stainless steel high-voltage electrodes that are either atomically clean or have N 30 8, and 2 150 8, surface oxide films. Argon ion etching and electron bombardment heating were available for in-situ surface cleaning, while an ellipsometric facility was used for characterizing electrode surfaces. Experimental results show that the efficiency of charge reversal is strongly dependant on both the thickness and electrical properties of surface oxide films.An associated theoretical analysis has established that these results can be explained in terms of a transient electron tunnelling mechanism, where the behaviour of a given electrode material is determined by its work-function and the bandgap and dielectric constant of its surface oxide.

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Field emission from metal particles in a vacuum gap

Cited by 20 publications

References 11 publications

Dynamics of microparticles in vacuum breakdown: Cranberg’s scenario updated by numerical modeling

Dynamics of microparticles in vacuum breakdown: Cranberg’s scenario updated by numerical modeling

Mechanism of impulse voltage breakdown in high voltage vacuum interrupters with long contact gap

The influence of surface oxidation on the electron tunnelling mechanism of microparticle charge reversal during a bouncing impact on a charged conductor

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