Sirse, Nishant (2013) Resonance hairpin probe for electronegative plasma diagnostics. PhD thesis, Dublin City University.
Abstract
The practical applications of resonance hairpin probe for characterizing electronegative plasma is investigated. In particular the hairpin probe was operated in a time-resolved
mode for measuring the electron density evolution during pulsed laser photodetachment of negative ions in an oxygen inductively coupled plasma (ICP) discharge. From the
temporal evolution of the electron density, the negative ion temperature is determined from the characteristic diffusion time of negative ions in the photodetached channel. This is compared with an independent method based on the temporal evolution of the plasma potential during photodetachment measured by a floating emissive probe.
Temporal evolution of negative oxygen ions in a pulsed dc magnetron discharge is also obtained using pulsed photodetachment and a time-resolved hairpin probe. The results are found to be in reasonably good agreement with those measured from Langmuir probe assisted photodetachment.
Two important applications addressed in this thesis are the use of steady state and pulse biased hairpin probes. For overcoming the limitations arising because of the finite sheath width around the resonator pins, the hairpin was systematically biased at strong negative dc potentials (eφ >> kTe) with respect to the plasma. A plot of resonance frequency verses probe bias is shown to provide a unique value for the electron density. Comparison of the sheath corrected electron density based on the step front sheath model and that obtained with a planar Child-Langmuir sheath
approximation, were found to be in good agreement at higher densities (above 1x10 16 m-3), however small deviations were observed at lower densities (below 3x1015 m-3) due
to deviation from a planar sheath assumption. Finally, qualitative measurement of negative ion parameters is performed by pulse biasing the hairpin probe. Comparison of
the temporal evolution of the electron density before and post application of a negative pulse bias allows one to obtain both the negative ion density, negative ion temperature, as well as the positive ion density. The relative measurements of the negative ion parameters using this technique are found to be in reasonably good agreement with the hairpin probe assisted laser photodetachment however the absolute measurements are underestimated by a factor of 10. The discrepancy in the measured absolute negative ion parameters and the limitations behind this technique are discussed.
Metadata
Item Type: | Thesis (PhD) |
---|---|
Date of Award: | March 2013 |
Refereed: | No |
Supervisor(s): | Karkari, Shantanu and Turner, Miles M. |
Uncontrolled Keywords: | inductively coupled plasma; ICP; hairpin probes |
Subjects: | Physical Sciences > Plasmas Physical Sciences > Plasma processing |
DCU Faculties and Centres: | DCU Faculties and Schools > Faculty of Science and Health > School of Physical Sciences |
Use License: | This item is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 License. View License |
Funders: | EURATOM |
ID Code: | 17734 |
Deposited On: | 05 Apr 2013 14:10 by Miles Turner . Last Modified 05 Apr 2013 14:10 |
Documents
Full text available as:
Preview |
PDF
- Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
6MB |
Downloads
Downloads
Downloads per month over past year
Archive Staff Only: edit this record