Time- and space-resolved light emission and spectroscopic research of the flashover plasma

Gleizer, J. Z.; Krasik, Ya. E.; Leopold, J. G.

doi:10.1063/1.4913213

Cited by 23 publications

(7 citation statements)

References 16 publications

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“…The results of these experiments support our previous work [1][2][3] in that they show that a small amount of primary electrons produced near the CTJ is sufficient to produce vacuum insulator surface flashover if the electric field accelerates them along this surface. If conditions exist that sufficient plasma forms at the ATJ and there is sufficient time and power for it to expand, acquire the anode potential, and shorten the anode cathode gap, flashover may develop.…”

Section: -4supporting

confidence: 86%

Initiation of vacuum insulator surface high-voltage flashover with electrons produced by laser illumination

Krasik

Leopold

2015

Physics of Plasmas

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In this paper, experiments are described in which cylindrical vacuum insulator samples and samples inclined at 45 relative to the cathode were stressed by microsecond timescale high-voltage pulses and illuminated by focused UV laser beam pulses. In these experiments, we were able to distinguish between flashover initiated by the laser producing only photo-electrons and when plasma is formed. It was shown that flashover is predominantly initiated near the cathode triple junction. Even dense plasma formed near the anode triple junction does not necessarily lead to vacuum surface flashover. The experimental results directly confirm our conjecture that insulator surface breakdown can be avoided by preventing its initiation [

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Section: -4supporting

confidence: 86%

Initiation of vacuum insulator surface high-voltage flashover with electrons produced by laser illumination

Krasik

Leopold

2015

Physics of Plasmas

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“…For a vacuum-dielectric system, high-field induced flashover is prone to take place on the insulator surface with a breakdown threshold much lower than the puncture voltage of both the vacuum gap and the solid dielectric with the same length [1][2][3], which primarily accounts for the failure of electrovacuum devices like vacuum interrupters, dielectric windows, pulsed-power devices [4][5][6], etc. This phenomenon has attracted great attention for more than half a century.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of vacuum flashover on surface roughness

Guo¹,

Sun²,

Zhang³

et al. 2019

J. Phys. D: Appl. Phys.

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An investigation is conducted regarding the influence of surface roughness on the flashover strength of an insulator in vacuum. A series of experiments is first presented, showing the relationship between surface roughness and flashover voltage, combined with measurement of surface potential distribution. It is found that surface charging on a roughened dielectric is suppressed remarkably; also the flashover voltage threshold depicts a rise-and-fall trend with roughness increasing, exhibiting a voltage summit at a certain roughness value. In addition, optical observation is implemented to draw a parallel with an electron trajectory in vacuum. A proposal can therefore be made that multipactor expansion tends to be mitigated as electron bombardment on a dielectric occurs with a lower secondary electron yield. Then a theoretical model considering the microscopic physical process is established to explain the above phenomena, consisting of an internal charge migration layer, an interfacial electron absorption layer and an external electron obstruction layer. The validity of this theoretical model can be confirmed by obtaining the surface trap distribution, microscopic morphology and net secondary electron yield.

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“…A multipactor due to secondary electron emission frequently appears over the surface of a material, giving rise to microwave breakdown as well as insulator failure in a vacuum, hindering further advancements in many areas like pulsed-power technology, high-power microwave (HPM), electrovacuum devices, satellite, etc [1][2][3][4][5]. The single-surface multipactor induces gas desorption in a vacuum, which produces a lowpressure plasma discharge along the dielectric surface, also referred to as a flashover [6][7][8][9]. Processes above the surface in a vacuum flashover caused by a multipactor have been consistently well expatiated in the secondary electron emission avalanche (SEEA) model in works over the years [8,[10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Estimation of surface flashover threshold in a vacuum II: flashover phase transition

Sun¹,

Guo²,

Li³

et al. 2019

J. Phys. D: Appl. Phys.

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Surface discharge in a vacuum occurs under an intense external field, also called a flashover. The flashover threshold over which the surface flashover occurs is of vital importance in the vacuum-solid interface. It is widely assumed that the flashover is initiated by a single surface multipactor and develops as a plasma discharge along a dielectric surface, namely the secondary electron emission avalanche (SEEA). Yet the SEEA model is not versatile for all practical vacuum-solid interfaces and there remain experiment results contradicting the theory predictions without a resolute answer. Here we further expand on previous theories and consider the conventional SEEA model under arbitrary field distributions. The example of a conical insulator is then given to test the validity of the SEEA model under an arbitrary field. It is found that the obtained flashover threshold is only consistent with the experiment at low cone angles where the field near the cathode triple junction is strong, while remarkable discrepancies appear when the anode field is significantly enhanced. The discrepancies can be understood if a different discharge model, i.e. an anode-initiated flashover (AIF) is included. Both particle-in-cell simulation and optical diagnostics are employed to visualize this unique discharge, which are then formalized on theoretical grounds to elucidate the early stage of the AIF. The transition between two flashover phases is then clarified. The plasma-surface interaction and sheath dynamics during the discharge are analyzed theoretically, showing distinct sheath evolutions in two flashover models. Additionally, a new factor reflecting field distortion is introduced to estimate the discharge threshold under an SEEA framework.

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Time- and space-resolved light emission and spectroscopic research of the flashover plasma

Cited by 23 publications

References 16 publications

Initiation of vacuum insulator surface high-voltage flashover with electrons produced by laser illumination

Initiation of vacuum insulator surface high-voltage flashover with electrons produced by laser illumination

Mechanism of vacuum flashover on surface roughness

Estimation of surface flashover threshold in a vacuum II: flashover phase transition

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