Similarity law for a homogeneous discharge in the presence of a strong field and analogues of the Stoletov constant for the pulsed regime

Yakovlenko, S. I.

doi:10.1134/s1054660x07030036

Cited by 22 publications

(10 citation statements)

References 11 publications

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“…4 are shorter than the ones calculated with the ionization frequency data from literature. 10,13 It is expected that the same mechanisms are active in argon as in nitrogen, i.e., a pressure dependent loss of photoelectrons for the case with UV illumination and a field dependent source of discharge initiating electrons. The fact that the measured formative times are substantially shorter than the calculated ones is probably due to higher "hard" UV emission of exited argon atoms, which in turn might be associated with an electron energy distribution function which is shifted to higher energies.…”

Section: B Argonmentioning

confidence: 96%

“…An equation for this ionization frequency for nitrogen as well as argon as a function of E eff / p has been adopted from literature. 10,13 If any avalanche reaches the critical density, the calculation is terminated and the time when this happens is recorded as delay time for this particular run. This procedure is repeated typically 40 times to generate a simulated distribution of delay times.…”

Section: Sampling Proceduresmentioning

confidence: 99%

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Investigation of the delay time distribution of high power microwave surface flashover

2011

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Characterizing and modeling the statistics associated with the initiation of gas breakdown has proven to be difficult due to a variety of rather unexplored phenomena involved. Experimental conditions for high power microwave window breakdown for pressures on the order of 100 to several 100 torr are complex: there are little to no naturally occurring free electrons in the breakdown region. The initial electron generation rate, from an external source, for example, is time dependent and so is the charge carrier amplification in the increasing radio frequency ͑RF͒ field amplitude with a rise time of 50 ns, which can be on the same order as the breakdown delay time. The probability of reaching a critical electron density within a given time period is composed of the statistical waiting time for the appearance of initiating electrons in the high-field region and the build-up of an avalanche with an inherent statistical distribution of the electron number. High power microwave breakdown and its delay time is of critical importance, since it limits the transmission through necessary windows, especially for high power, high altitude, low pressure applications. The delay time distribution of pulsed high power microwave surface flashover has been examined for nitrogen and argon as test gases for pressures ranging from 60 to 400 torr, with and without external UV illumination. A model has been developed for predicting the discharge delay time for these conditions. The results provide indications that field induced electron generation, other than standard field emission, plays a dominant role, which might be valid for other gas discharge types as well.

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Section: B Argonmentioning

confidence: 96%

Section: Sampling Proceduresmentioning

confidence: 99%

Investigation of the delay time distribution of high power microwave surface flashover

2011

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“…To provide an example of this, a flashover plasma induced by a 11.4 kV/cm peak field RF pulse in N 2 at 60 Torr has a momentum transfer collision frequency of 575 GHz and an ionization frequency of 3.7 GHz, as calculated using the scaling laws by Yakovlenko. 10 In addition to ionization rates and momentum transfer collision rates, Bolsigþ also provides scaling laws for diffusion coefficients as a function of electric field and gas type/ density. Axial diffusion as an electron transport (and loss) mechanism is observed in simulations to be significant, and is incorporated directly into the simulation via a subroutine as follows:…”

Section: Dtmentioning

confidence: 99%

“…The boundary conditions for Eqs. (9) and (10) When calculating v c for nitrogen and argon using the equations given by Yakovlenko, 10 it is necessary to use a scaling law derived from the drift velocity u ed where this average velocity can be found by the relationship:…”

Section: Dtmentioning

confidence: 99%

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A finite-difference time-domain simulation of high power microwave generated plasma at atmospheric pressures

et al. 2012

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A finite-difference algorithm was developed to calculate several RF breakdown parameters, for example, the formative delay time that is observed between the initial application of a RF field to a dielectric surface and the formation of field-induced plasma interrupting the RF power flow. The analysis is focused on the surface being exposed to a background gas pressure above 50 Torr. The finite-difference algorithm provides numerical solutions to partial differential equations with high resolution in the time domain, making it suitable for simulating the time evolving interaction of microwaves with plasma; in lieu of direct particle tracking, a macroscopic electron density is used to model growth and transport. This approach is presented as an alternative to particle-in-cell methods due to its low complexity and runtime leading to more efficient analysis for a simulation of a microsecond scale pulse. The effect and development of the plasma is modeled in the simulation using scaling laws for ionization rates, momentum transfer collision rates, and diffusion coefficients, as a function of electric field, gas type and pressure. The incorporation of plasma material into the simulation involves using the Z-transform to derive a time-domain algorithm from the complex frequency-dependent permittivity of plasma. Therefore, the effect of the developing plasma on the instantaneous microwave field is calculated. Simulation results are compared with power measurements using an apparatus designed to facilitate surface flashover across a polycarbonate boundary in a controlled N2, air, or argon environment at pressures exceeding 50 Torr.

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Statistical analysis of high power microwave surface flashover delay times in nitrogen with metallic field enhancements

2011

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The physical mechanisms that contribute to atmospheric breakdown induced by high power microwaves (HPMs) are of particular interest for the further development of high power microwave systems and related technologies. For a system in which HPM is produced in a vacuum environment for the purpose of radiating into atmosphere, it is necessary to separate the atmospheric environment from the vacuum environment with a dielectric interface. Breakdown across this interface on the atmospheric side and plasma development to densities prohibiting further microwave propagation are of special interest. In this paper, the delay time between microwave application and plasma emergence is investigated. Various external parameters, such as UV illumination or the presence of small metallic points on the surface, provide sources for electron field emission and influence the delay time which yields crucial information on the breakdown mechanisms involved. Due to the inherent statistical appearance of initial electrons and the statistics of the charge carrier amplification mechanisms, the flashover delay times deviate by as much as ±50% from the average, for the investigated case of discharges in N2 at pressures of 60–140 Torr and a microwave frequency of 2.85 GHz with 3 μs pulse duration, 50 ns pulse risetime, and MW/cm2 power densities. The statistical model described in this paper demonstrates how delay times for HPM surface flashover events can be effectively predicted for various conditions given sufficient knowledge about ionization rate coefficients as well as the production rate for breakdown initiating electrons.

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Similarity law for a homogeneous discharge in the presence of a strong field and analogues of the Stoletov constant for the pulsed regime

Cited by 22 publications

References 11 publications

Investigation of the delay time distribution of high power microwave surface flashover

Investigation of the delay time distribution of high power microwave surface flashover

A finite-difference time-domain simulation of high power microwave generated plasma at atmospheric pressures

Statistical analysis of high power microwave surface flashover delay times in nitrogen with metallic field enhancements

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