Different approach to pulsed high-voltage vacuum-insulation design

Leopold, J. G.; Leibovitz, C.; Navon, I.; Markovits, M.

doi:10.1103/physrevstab.10.060401

Cited by 29 publications

(6 citation statements)

References 15 publications

(21 reference statements)

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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%

“…We conjectured that by deflecting these primary electrons away from the insulator surface the breakdown properties of the vacuum insulator could be improved. 1 Since we assume that electrons are the most common breakdown initiators, our conjecture excluded anode triple junction (ATJ) initiation. Recently, 2 by measuring the flashover breakdown electric fields over various insulator arrangements using a conditioning method, we experimentally demonstrated that for high voltage pulses of a microsecond time scale duration, initiation is indeed predominantly at the cathode triple junction (CTJ).…”

Section: Introductionmentioning

confidence: 99%

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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%

Section: Introductionmentioning

confidence: 99%

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

Krasik

Leopold

2015

Physics of Plasmas

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“…On the basis of previous studies with respect to flashover development, methods to improve the flashover threshold or increase the flashover voltage contain either a multipactor suppression or a field-optimization-reducing emission from the CTJ. While various researchers have capitalized on the refined secondary emission yield (SEY) [30,31] or external fields [32,33] to constrain the formation of the multipactor, methods including insulator shape redesign and structural modification near the CTJ have been employed as well to reduce the field near the CTJ [34,35]. Yet flashover can still occur even when the cathode field is significantly reduced, as reported in previous experiments [36][37][38][39][40], which seemingly contradicts the SEEA model.…”

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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“…In Ref. 6, it was suggested that voltage holdoff will considerably improve if primary electrons are deflected away from impacting while at the same time secondary electrons are accelerated away from the insulator surface so these electrons cannot restrike. Such a scheme is made possible by appropriate design of the orientation of the electric and magnetic fields near the insulator surface.…”

Section: Introductionmentioning

confidence: 99%

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

Gleizer

Krasik

Leopold

2015

Journal of Applied Physics

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The results of an experimental study of the evolution of surface flashover across the surface of an insulator in vacuum subject to a high-voltage pulse and the parameters of the flashover plasma are reported. For the system studied, flashover is always initiated at the cathode triple junctions. Using time-resolved framing photography of the plasma light emission the velocity of the light emission propagation along the surface of the insulator was found to be $2.5Á10 8 cm/s. Spectroscopic measurements show that the flashover is characterized by a plasma density of 2-4 Â 10 14 cm À3 and neutral and electron temperatures of 2-4 eV and 1-3 eV, respectively, corresponding to a plasma conductivity of $0.2 X À1 cm À1 and a discharge current density of up to $10 kA/cm 2 . V C 2015 AIP Publishing LLC. [http://dx.08:05:16 FIG. 3. Typical waveforms of voltage (a), current (b), and fast camera synchronized pulse (c) for the case of 15 mm polypropylene sample. FIG. 4. Images of flashover plasma along a 15 mm high, 50 mm diameter Polypropylene sample. (a) t d % 4 ns, MCP voltage: 860 V; (b) t d % 8 ns, MCP voltage: 860 V; (c) t d % 26 ns, MCP voltage: 750 V; (d) t d % 34 ns, MCP voltage: 750 V. Frame duration is 5 ns.

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Different approach to pulsed high-voltage vacuum-insulation design

Cited by 29 publications

References 15 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

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

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

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