Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session QR1: Microwave Discharges II |
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Chair: Alok Ranjan, TEL Technology Center America Room: Ballroom I |
Thursday, October 3, 2013 3:30PM - 3:45PM |
QR1.00001: Investigation of Microplasma Instabilities at 1 GHz Chen Wu, Jeffrey Hopwood Microwave microplasmas have been operated stably in excess of 2000 hours using less than one watt of power. Plasmas at atmospheric pressure and high power density, however, are subject to ionization overheating instability followed by a destructive glow-to-arc transition. We describe steady-state atmospheric pressure microplasmas in non-flowing argon and air driven by up to 40 watts of microwave power. These discharges are supported by either a quarter-wave microstrip resonator or a microstrip transmission line. Models show that the resonator configuration rejects excess power and remains unconditionally stable. The transmission line, however, couples power efficiently to a plasma of $\sim$100 $\Omega $ and produces a more intense discharge. Electrodes of copper, aluminum and lead-based solder are investigated on both polymer and alumina substrates. Copper and lead electrodes may be evaporated by a high power microdischarge as seen by optical emission. These conditions uniquely result in severe electrode damage. Microdischarges supported on polymer substrates show C$_{2}$, CN and CH emission but alumina substrates are unaffected by the microplasma. These results show that steady-state microwave discharges can be stable at very high power density provided that copper microelectrodes and ceramic substrates are employed. [Preview Abstract] |
Thursday, October 3, 2013 3:45PM - 4:00PM |
QR1.00002: VUV Photon Fluxes from Microwave Excited Microplasmas at Low Pressure Peng Tian, Mark Denning, Randall Urdhal, Mark J. Kushner Microplasmas in rare gases and rare gases mixtures can provide efficient and discretely tunable sources of VUV light. Microwave excited microplasma sources excited by a split-ring resonator antenna in rare gas mixtures operated in ceramic cavities with sub-mm dimensions have been developed as discretely tunable VUV sources for chemical analysis. Controlling wavelengths and the ratio of ion to VUV fluxes are important to achieving chemical selectivity. In this paper, we will discuss results from an investigation of scaling laws for the efficiency of VUV photon production in rare gas mixtures. The investigation was performed using a hydrodynamics model where the electron energy distribution and radiation transport are addressed by Monte Carlo simulations. Plasma density, VUV photon production and fluxes from the cavities will be discussed for mixtures of Ar, He, Xe, Kr, and as a function of power format (pulsing, cw), pressure and cavity sizes. [Preview Abstract] |
Thursday, October 3, 2013 4:00PM - 4:15PM |
QR1.00003: Time-resolved microplasma excitation temperature in a pulsed microwave discharge Jeffrey Hopwood, Shabnam Monfared, Alan Hoskinson Microwave-driven microplasmas are usually operated in a steady-state mode such that the electron temperature is constant in time. Transient measurements of excitation temperature and helium emission lines, however, suggest that short microwave pulses can be used to raise the electron energy by 20-30{\%} for approximately 100ns. Time-resolved optical emission spectrometry reveals an initial burst of light emission from the igniting microplasma. This emission overshoot is also correlated with a measured increase in excitation temperature. Excimer emission lags atomic emission, however, and does not overshoot. A simple model demonstrates that an increase in electron temperature is responsible for the overshoot of atomic optical emission at the beginning of each microwave pulse. The formation of dimers and subsequent excimer emission requires slower three-body collisions with the excited rare gas atom; this is why excimer emission does not overshoot the steady state value. Similar experimental and modeling results are observed in argon gas. The overshoot in electron temperature may be used to manipulate the collisional production of species in microplasmas using short, low-duty cycle microwave pulses. [Preview Abstract] |
Thursday, October 3, 2013 4:15PM - 4:30PM |
QR1.00004: Harmonic Generation by Microwave-frequency Microplasma Stephen Parsons, Alan Hoskinson, Jeffrey Hopwood A microplasma may operate as a nonlinear circuit element and generate power at the harmonics of the drive frequency. As an example, microplasma is sustained using 1 W of power at 1.3 GHz in a small discharge gap formed in a split-ring resonator. A probe extends into the microplasma and extracts the 3$^{\mathrm{rd}}$ harmonic power through a tuned resonator at 3.9 GHz. The experimental data show that this non-optimized system produces a $+$38 dB increase in 3$^{\mathrm{rd}}$ harmonic power in the presence of a microplasma. Two origins of nonlinearity are described: the harmonic conduction current due to electron collection by microelectrodes, and the harmonic displacement current due to the voltage-dependent sheath capacitance. PIC-MC simulations suggest that the microplasma nonlinearity may also be exploited at frequencies of 100 GHz. [Preview Abstract] |
Thursday, October 3, 2013 4:30PM - 4:45PM |
QR1.00005: Microwave-driven plasmas in Hollow-Core Photonic Crystal Fibres L.L. Alves, O. Leroy, C. Boisse-Laporte, P. Leprince, B. Debord, F. Gerome, R. Jamier, F. Benabid This paper reports on a novel solution to ignite and maintain micro-plasmas in gas-filled Hollow-Core Photonic Crystal Fibres (HC-PCFs), using CW microwave excitation (2.45 GHz) [1]. The original concept is based on a surfatron, generating argon micro-plasmas of few centimetres in length within a $100\;\mu m$ core-diameter Kagome HC-PCF, at $\sim $1 mbar on-gap gas-pressure using low powers (\textless\ 50 W). Diagnostics of the coupled power evidence high ionization degrees ($\sim $10$^{-2})$, for moderate gas temperatures ($\sim $1300 K at the centre of the fibre, estimated by OES), with no damage to the host structure. This counter intuitive result is studied using a 1D-radial fluid model that describes the charged particle and the electron energy transport, the electromagnetic excitation and the gas heating [2,3]. We analyze the modification of the plasma and the gas heating mechanisms with changes in the work conditions (core diameter, pressure and electron density). \\[4pt] [1] B. Debord et al, ECOC conference Mo.2.LeCervin.5. (2011)\\[0pt] [2] L.L. Alves et al, Phys. Rev. E \textbf{79}, 016403 (2009) \\[0pt] [3] J. Greg\'{o}rio et al, Plasma Sources Sci. Technol. \textbf{21}, 015013 (2012) [Preview Abstract] |
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