Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session RR4: Electro-Magnetic Interactions with Plasmas IFocus
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Chair: Bert Ellingboe, Dublin City University Room: 3 |
Thursday, October 13, 2016 11:00AM - 11:30AM |
RR4.00001: Peering inside microplasmas sustained by microwaves, millimeter waves and beyond Invited Speaker: Jeffrey Hopwood Atmospheric microplasmas are experimentally investigated over a range of excitation frequency from 0.5 to 12 GHz. A validated fluid model correctly predicts the measured electron density in this band of operation. This model is then extended to predict plasma behavior up to 0.4 THz. At constant power (0.25 W), the central electron density increases to 5x10$^{\mathrm{14}}$ cm$^{\mathrm{-3}}$ as the microwave frequency increases toward the electron energy dissipation frequency of 5 GHz (in argon). Above 5 GHz, the argon plasma density remains approximately constant, but the electrode voltage decreases to less than 5 volts in amplitude. This is remarkable in that the microwave potential is less than the excitation potential of argon. In the millimeter wave band, we observe series resonance between the plasma inductance and sheath capacitance at \textasciitilde 30 GHz. The parallel resonance results in strong electron oscillation within the microplasma at the position where the electron plasma frequency is equal to the excitation frequency (\textasciitilde 200 GHz). Crossing resonance boundaries changes the nature of the microplasma impedance between capacitive, resistive, and inductive. In addition to linear behavior, we also present models and measurements of microplasma nonlinearity. Nonlinearity generates harmonic plasma currents and is due primarily to dynamic sheath expansion and electron conduction currents. In total, the microplasma provides a rich variety of electromagnetic behaviors that can be incorporated into plasma-reconfigurable metamaterials and photonic crystals. [Preview Abstract] |
Thursday, October 13, 2016 11:30AM - 11:45AM |
RR4.00002: Abnormal glow discharge as a variable capacitor for tunable RF systems Sergey Macheret, Abbas Semnani, Dimitrios Peroulis For frequency-tunable resonators and filters in high-power applications, conventional semiconductor devices are easily damaged, while mechanically-tunable systems are bulky and slow. In this regard, weakly ionized plasmas can offer an attractive solution. In this work, an LC resonator circuit where a commercial gas discharge tube (GDT) serves as a variable capacitor was studied experimentally and theoretically. The experiments show continuous decrease of the resonant frequency by up to 50 percent with increase in the DC current through the GDT. Analysis of the current-voltage characteristic and the breakdown parameters, combined with lumped-parameter equivalent-circuit RF simulations, allowed us to determine the gas pressure, the electrode coating material and the secondary emission coefficient, and to achieve a very good agreement between the calculated and measured transmittance values. The analysis reveals that reduction in the cathode sheath thickness with increase in the DC current in the abnormal glow discharge regime is the key factor responsible for the experimentally observed tunability. [Preview Abstract] |
Thursday, October 13, 2016 11:45AM - 12:00PM |
RR4.00003: Numerical modeling of high power breakdown in metamaterials. Konstantinos Kourtzanidis, Dylan Pederson, Laxminarayan Raja Metamaterials consist of sub-wavelength structural inclusions layered in a periodic fashion, which provide an effective response to electromagnetic (EM) radiation. The electric or magnetic responses of these materials are based on the resonant nature of their constitutive micro-structures. Under high power EM radiation, these resonances can result in the production of high amplitude currents and field amplification. Depending on the background gas and supporting pressure, breakdown can occur. The formation of plasma can strongly modify the EM response of the metamaterial and thus a detailed study on the breakdown threshold, plasma localization and EM response modification is necessary. Here, we present three-dimensional numerical simulations of high power -- high frequency air breakdown in metamaterials. We use a self-consistent fluid description of the plasma formation and dynamics coupled with Maxwell's equations via the electron momentum equation. We study two typical (for metamaterials) micro-structures: The Split Ring Resonator and the Cut Wire pairs. Breakdown threshold is identified for both configurations. Calculations of transmittance and retrieval of the metamaterials' effective parameters help us quantify the effect of plasma formation on the EM response of these metamaterials. [Preview Abstract] |
Thursday, October 13, 2016 12:00PM - 12:15PM |
RR4.00004: Plasma-Based Tunable High Frequency Power Limiter Abbas Semnani, Sergey Macheret, Dimitrios Peroulis Power limiters are often employed to protect sensitive receivers from being damaged or saturated by high-power incoming waves. Although wideband low-power limiters based on semiconductor technology are widely available, the options for high-power frequency-selective ones are very few. In this work, we study the application of a gas discharge tube (GDT) integrated in an evanescent-mode (EVA) cavity resonator as a plasma-based power limiter. Plasmas can inherently handle higher power in comparison with semiconductor diodes. Also, using a resonant structure provides the ability of having both lower threshold power and frequency-selective limiting, which are important if only a narrowband high-power signal is targeted. Higher input RF power results in stronger discharge in the GDT and consequently higher electron density which results in larger reflection. It is also possible to tune the threshold power by pre-ionizing the GDT with a DC bias voltage. As a proof of concept, a 2-GHz EVA resonator loaded by a 90-V GDT was fabricated and measured. With reasonable amount of insertion loss, the limiting threshold power was successfully tuned from 8.3 W to 590 mW when the external DC bias was varied from 0 to 80 V. The limiter performed well up to 100 W of maximum available input power. [Preview Abstract] |
Thursday, October 13, 2016 12:15PM - 12:30PM |
RR4.00005: Control of powerful microwaves using EBG plasma structures. Leanid Simonchik, Thierry Callegari, Jerome Sokoloff, Maxim Usachonak Glow discharge plasmas have great potential for application as control elements in microwave devices designed on the basis of electromagnetic band gap (EBG) structures. In this report, a plasma control of powerful microwave propagation by means of 1D and 2D EBG structures is under investigation. Three pulsed discharges in argon (or helium) at atmospheric pressure are applied in the capacity of plasma inhomogeneities. Temporal behavior of electron concentration in discharge is determined. The transmission spectra of 1D EBG structure formed solely by plasma in the X-waveguide are measured. The amplitudes of short (\textasciitilde 200 ns) and powerful (50 kW) microwave pulses at frequency of 9.15 GHz are strongly suppressed (more than on 40 dB) when plasma structure exists. The propagation of these powerful microwave pulses through the triangular metallic 2D EBG structure with the plasma control elements is investigated, too. It is shown that the transmission of the 2D EBG structure at the angle of 45$^{\mathrm{o}}$ ceases quickly (during a few tenth of nanoseconds) when plasma acts as a compensator of defect in the front row of the structure. On the contrary, the transmission arises quickly once plasma acts as an additional defect. [Preview Abstract] |
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