Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session MT2: Glows I |
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Chair: T. Gans, Ruhr University - Bochum Room: Doubletree Hotel Cedar |
Tuesday, October 18, 2005 4:00PM - 4:15PM |
MT2.00001: Thomson scattering and simulation study of electron energy distribution near the dielectric plate of a planar surface wave plasma source A. Kono, T. Otsuki, R. Lee, J. Kobayashi, M. Aramaki Planar surface wave plasma (SWP) is expected to be a promising plasma source producing large-area low-electron-temperatures plasma for materials processing. To clarify the electron heating mechanism in SWP, Thomson scattering measurements and Monte-Carlo simulation study are carried out. A mechanism believed to be responsible for electron heating is the existence of a thin resonance layer near or in the sheath region where the local electron plasma frequency equals the microwave frequency and hence the microwave electric field is enhanced. In the simulation, first the microwave electric field is estimated by solving the fluid equations for electron motion and then carrying out Monte-Carlo simulation in the estimated electric field to obtain the electron energy distribution. The results of simulation indicate that average energy increases near the dielectric plate as observed in Thomson scattering measurements. The electron energy distribution obtained in the simulation (with the effect of Coulomb collision included) is nearly Maxwellian and does not show a high energy hump as reported in some probe studies. (Work supported by 21st Century COE Program from MEXT Japan) [Preview Abstract] |
Tuesday, October 18, 2005 4:15PM - 4:30PM |
MT2.00002: Time-Resolved Studies of Pulsed Plasmas Jose Lopez, WeiDong Zhu, Biswa N. Ganguly, Peter Bletzinger, James M. Williamson, Abraham Belkind, Kurt H. Becker A periodic reversal of the voltage applied to an electrode during the application of pulsed direct current (DC) power has been shown to diminish the buildup of charge due to the attraction of oppositely charged particles in the reverse pulse. This technique has been widely used to reduce arcing caused by charge buildup, especially in reactive magnetron sputtering of dielectric films. A more recent application has been the application of very short DC pulses of voltages much higher than the breakdown voltage to dielectric barrier discharges (DBD). The resulting very high, but short-lived electric fields can enhance radical generation and the intensity of UV radiation emitted by the plasma. In an effort to better understand the effects of frequency, pulse width, and duty cycle on magnetron sputtering and DBDs, time-resolved electrical measurements and optical plasma emission spectroscopy and imaging were carried out using a fast intensified CCD (ICCD) camera. The effects of the pulsed DC power on the physical processes of both types of plasmas will be discussed in this work. [Preview Abstract] |
Tuesday, October 18, 2005 4:30PM - 4:45PM |
MT2.00003: Shockwave interactions with ionization waves in argon glow discharges Nicholas Siefert, Biswa Ganguly We report measurements of enhancement in both optical emission and electric field at the shock front of weak shock waves (M$\sim $2) propagating in a 2 Torr argon glow discharge. The enhancements depend on when the shockwave arrives at the observation point because of the electric field modulation by the ionization wave. The ionization waves create large-amplitude fluctuations of the electron temperature and electron number density, which are modulated out of phase in order to conserve discharge current. This creates a plasma where the local electron Debye length fluctuates by nearly an order of magnitude without changing global properties, such as Mach number, gas pressure, and gas temperature. Depending on the timing between the ionization wave and the shockwave arrival, the local electron Debye length at the shock front can fluctuate between being either greater than or less than the shock thickness. The shockwave-induced enhancement in optical emission intensity and the electric field were found to exceed the modulation caused by the ionization wave itself only if the shockwave arrives when the Debye length is a maximum in the ionization wave. These measurements shows that, under a certain range of electron Debye length, shock thickness, and electron-neutral collision mean free path, there is an increase in the already non-equilibrium energy of the electrons at the shock front. [Preview Abstract] |
Tuesday, October 18, 2005 4:45PM - 5:00PM |
MT2.00004: Spectrometric analysis and kinetic modelling of an O$_2$-N$_2$ discharge Chanel Hayden, Derek Monahan, Miles M. Turner, Andrey Islyaikin, Albert R. Ellingboe Low pressure O$_2$-N$_2$ plasmas are widely used in a number of industrial processes such as surface treatment, cleaning and polymer etching. In this paper we will present an experimental analysis of an ashing discharge via mass spectrometry and optical emission spectrometry. The equipment under analysis comprises of an upstream microwave-rf downstream configuration at an operating pressure of 850~mT. Diagnostics were applied to the downstream chamber and a number of measurements taken for a range of microwave-rf power values and varying gas fractions. Resultant neutral species present in the discharge (N, O, NO, N$_2$O, NO$_2$) were analysed throughout this range of physical conditions. A general global model, currently under development, was used to simulate the experiment by means of a complex chemistry data set. It was found that the model was very sensitive to chemistry inputs, as such resulting outputs may well be deemed unreliable. Further investigation of the reliability of chemistry sets through validation by experimental assessment is central to the relevance of data obtained from global models. [Preview Abstract] |
Tuesday, October 18, 2005 5:00PM - 5:15PM |
MT2.00005: Balmer series emission in the afterglow of high-pressure, laser-induced hydrogen and hydrogen-argon plasmas Lutz H\"{u}wel, Tom Morgan, Bill Graham The afterglow of photoionised plasmas created in hydrogen and hydrogen with a small fractional addition of Ar (3.5 {\%} ) has been studied by focussing a 15 ns, 10 Hz, 1064 nm laser pulse into gas that is at a pressure of 10$^{5 }$Pa. At the focus, the laser power density is about 10$^{11}$ W/cm$^{2}$. Light emission is dispersed by a 0.6 m monochromator, with a 1220 line/mm grating blazed at 500 nm and detected using an image-intensified linear diode. In pure hydrogen, H$\alpha $, H$\beta $, and H$\gamma $ emission was observed to about 4 $\mu $s. In the mixture, the peak emission intensity is enhanced by a factor of about 2, H$\delta $ and H$\varepsilon $ lines are also observed, and the emission of the H$\alpha $ and H$\gamma $ was observable to about 6 $\mu $s. The electron density, determined from Stark-broadening, is found to have a complex temporal behaviour. From an initial value at 0.3 $\mu $s of about 3.5$\times $10$^{16}$ cm$^{-3}$ in pure hydrogen and 6.5$\times $10$^{16}$ cm$^{-3}$ in the H$_{2}$/Ar mixture, the density falls by an order of magnitude by 1.5 $\mu $s. Thereafter, in pure hydrogen, an increase in density by about 1$\times $10$^{15}$ cm$^{-3}$ over a period of about 1 $\mu $s is observed, followed by a decrease. In the mixture, a plateau occurs in the density temporal behaviour. It is also found that the line emission intensity decay rate changes at about 1.5 $\mu $s (pure). WG was a Mellon Fellow at Wesleyan University. [Preview Abstract] |
Tuesday, October 18, 2005 5:15PM - 5:30PM |
MT2.00006: Enhanced Plasma Transport due to Neutral Depletion Amnon Fruchtman, Gennady Makrinich, Pascal Chabert, Jean-Marcel Rax The dynamics of plasma and neutral-gas in pressure balance are solved self-consistently to reveal the impact of neutral depletion. Analytical relations that determine the electron temperature, the rate of ionization, and the plasma density are derived. For the governing non- linear diffusion equation an analytical solution in the form of Kepler's equation is found. A generalized Schottky condition is derived in which the total number of neutrals, rather than the Paschen parameter, controls the electron temperature. It is shown that even if the plasma is weakly- ionized (typically 1{\%}), neutral depletion dramatically modifies the discharge equilibrium. Due to the inherent coupling of ionization and transport, an increase of the energy invested in ionization can nonlinearly enhance the transport process. We show that such an enhancement of the plasma transport due to neutral depletion can result in an unexpected \textit {decrease} of the plasma density when power is\textit{ increased}, despite the increase of the flux of generated plasma. [Preview Abstract] |
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