Electron beam probe measurements of electric fields in rf discharges
An electron beam diagnostic has been developed to measure small electric fields (<20 V/cm) in low pressure capacitive rf discharges. The electron beam diagnostic is described, and data are presented showing (1) the existence of transient double layers at the sheath boundary, and (2) evidence for a negative bulk plasma resistance. The electric field measurements motivated more careful measurements of the discharge current waveforms. The current waveforms, together with the electric field measurements, provide evidence for negative bulk plasma resistance. The current measurements allowed comparison between experimental discharge impedenace data and results from a global discharge model. This includes a reformulation of the secondary electron contribution to the electron power balance, and incorporation of electrode asymmetry. The results of this model are compared to experimental results obtained from current and voltage measurements. The model predictions of current amplitude and phase shift at the first harmonic fit experimental results surprisingly wellforo realistic values of the secondary emission coefficient. In particular, it is also shown how an additional electron coefficient. It is shown how an additional electron energy deposition mechanism can result in a more linear current (I) to voltage (V) amplitude relation. A two-coupled-sheath model is presented that qualitatively describes current conduction through asymmetric discharges. Some results of this model are: (1) The time-averaged sheath voltages are somewhat insensitive to the shape of the current waveform. (2) At moderate area ratios the current waveforms can maintain top-bottom symmetry if the driving voltage is allowed to distort slightly, and the external circuit prevents free circulation of the higher harmonic components of the current. (3) At higher area ratios the top-bottom symmetry of the current waveform is difficult to preserve since the system is so close to being a single sheath.
- Research Organization:
- California Univ., Berkeley, CA (United States)
- OSTI ID:
- 7196656
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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