Understanding and Improving High Voltage Vacuum Insulators for Microsecond Pulses

Javedani, J.B.; Goerz, D.A.; Houck, T.; Lauer, E.J.; Speer, R.D.; Tully, L.K.; Vogtlin, G.E.; White, A. D.

doi:10.2172/902244

Cited by 5 publications

(7 citation statements)

References 13 publications

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“…In Ref. 12, fast framing imaging was applied to estimate the velocity of the plasma front propagation along the surface of polyethylene or polycarbonate insulator inclined to b C ¼ 45 .…”

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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“…In Ref. 12, fast framing imaging was applied to estimate the velocity of the plasma front propagation along the surface of polyethylene or polycarbonate insulator inclined to b C ¼ 45 .…”

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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“…Investigating surface flashover has received much attention due to its importance in high voltage and pulsed power systems [2][3][4][5][6][7][8][9][10]. Although many of the mechanisms involved in surface flashover are believed to be understood, there are currently no reliable models to predict when insulators will fail or the optimum design under operational conditions [7].…”

Section: Introductionmentioning

confidence: 99%

“…One reason for not having a predictable model is due to the many different physical processes involved in flashover [2,7,[8][9][10]12]. The order of importance of the physical phenomena may also change for different operating conditions.…”

Section: Introductionmentioning

confidence: 99%

“…We have implemented several physics modules in VORPAL and applied them to investigate the surface flashover problem. Figure 1 shows pictures taken in the pulsed power lab at LLNL of a typical setup used to find the breakdown voltage of a +45° angled insulator as well as pictures demonstrating anode and cathode initiated flashover events [2]. In order to focus our attention on the physics involved in flashover, we will restrict ourselves in this discussion to slab like geometries where an insulator is placed between two electrodes of a planar parallel plate waveguide.…”

Section: Introductionmentioning

confidence: 99%

“…Pictures from[2] showing a typical setup to measure breakdown voltage as well as anode and cathode initiated breakdown across the surface of a +45° insulator. _______________________________ This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.…”

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Progress on simulating the initiation of vacuum insulator flashover

Perkins

Houck

Javedani

et al. 2009

2009 IEEE Pulsed Power Conference

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Vacuum insulators are critical components in many pulsed power systems. The insulators separate the vacuum and non-vacuum regions, often under great stress due to high electric fields. The insulators will often flashover at the dielectric vacuum interface for electric field values much lower than for the bulk breakdown through the material. Better predictive models and computational tools are needed to enable insulator designs in a timely and inexpensive manner for advanced pulsed power systems. In this article we will discuss physics models that have been implemented in a PIC code to better understand the initiation of flashover. The PIC code VORPAL [1] has been ran on the Linux cluster Hera at LLNL. Some of the important physics modules that have been implemented to this point will be discussed for simple angled insulators. These physics modules include field distortion due to the dielectric, field emission, secondary electron emission, insulator charging, and the effects of magnetic fields. In the future we will incorporate physics modules to investigate the effects of photoemission, electron stimulated desorption, and gas ionization. This work will lead to an improved understanding of flashover initiation and better computational tools for advanced insulator design.

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Spectroscopic investigation of early light emission from anode-initiated surface flashover in vacuum

Clark,

Mounho,

Brooks

et al. 2024

Physics of Plasmas

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Time-resolved optical emission spectroscopy is used to explore the early development of anode-initiated flashover in vacuum. An experimental apparatus for collecting flashover self-luminosity is introduced, which enables spatially resolved light collection from regions adjacent to the anode and cathode triple junctions. The emitted light is spectrally and temporally resolved utilizing an imaging spectrograph and a fast electronic shutter camera. The first light detectable from flashovers across both Rexolite and polytetrafluoroethylene (PTFE) insulators begins less than 10 ns prior to the flashover gap's impedance collapse and consists of faint broadband feature in primarily visible wavelengths. This suggests luminosity due to excitation in the solid, possibly occurring as a result of field emitted electrons. In the few nanoseconds leading up to and including the impedance collapse, the broadband spectrum grows in intensity and extends into the UV, eventually accompanied by a few emission lines of the insulator material. This is strong evidence that the early stages of anode-initiated flashover include surface layer breakdown of the insulator, as a contrast from cathode-initiated flashover, which is predominately an above-surface process. Spectra accumulated over longer exposures of PTFE flashovers indicate that, in the first few hundred nanoseconds after the impedance collapse, ions from the insulator material constitute the majority of the emission lines. Later, neutral and ionic metal species from the electrode contribute with similar prominence as well as molecular bands from diatomic carbon. Finally, a comparison is provided of the results of these studies to other spectroscopic investigations of vacuum flashover from the literature.

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Understanding and Improving High Voltage Vacuum Insulators for Microsecond Pulses

Cited by 5 publications

References 13 publications

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

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

Progress on simulating the initiation of vacuum insulator flashover

Spectroscopic investigation of early light emission from anode-initiated surface flashover in vacuum

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