Events at Physics

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Events on Friday, November 16th, 2012

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (
Host: Peter Timbie
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Physics Department Colloquium
Physics at the edge: Plasmas with dynamic sheaths
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Uwe Czarnetzki, Ruhr University Bochum
Abstract: Plasmas generated by applying a radio-frequency potential across a gas at low pressure between two electrodes are called capacitively coupled plasmas (CCP). They find frequent application in semiconductor and solar-cell production and other fields of industry. The physics of CCPs is dominated by the non-linear dynamics of the space-charge sheaths in front of the electrodes. This dynamics determines the ion as well as the electron energy distribution function, provides the main stochastic electron heating mechanism, and is also essential for trapping of energetic electrons. If a certain asymmetry between the sheaths at the two electrodes exists, the non-linearity leads to self-generated high frequency current oscillations which can strongly enhance the electron heating. Usually the asymmetry results from the geometrical size of the electrodes. However, by applying non-sinusoidal waveforms the symmetry can be broken even in the case of geometrical symmetry. This so called aEurooeelectrical asymmetry effectaEuro provides a simple and elegant way of external control where in particular the ion energy can be adjusted. The underlying physics will be explained by experimental results, analytical models, and particle-in-cell/Monte-Carlo simulations.
Host: Lin
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