THOMSON MICROWAVE SCATTERING FOR DIAGNOSTICS OF SMALL PLASMA OBJECTS ENCLOSED WITHIN GLASS TUBES
A specific class of small-scale plasmas (column diameters in a sub-mm to mm range) at rarefied pressures (under 10 Torr) enclosed in glass tubes hold significant interest currently in the scope of tunable plasma devices. Specifically, applications of these plasmas include plasma antennas and plasma photonic crystals. Reliable diagnostics are necessary for the development and implementation of these technologies as conventional tools are inadequate in such small-scale plasmas.
Coherent microwave scattering in the Thomson regime (TMS) was recently demonstrated for diagnostics of electron number density in miniature free-standing laser-induced plasmas in air under 10 Torr with plasma column diameters < 0.5 mm. However, measurements by TMS diagnostics have never been applied for small-scale plasma objects enclosed within glass tubes. Additionally, TMS measurements were never independently confirmed with a previously verified experimental technique. This work aims to validate results of TMS measurements for small-scale plasma objects enclosed within glass tubes using the previously established and well-known hairpin resonator probe. A DC discharge plasma column of fairly large diameter (about 1.5 cm) is used in the experiments to ensure reliable non-intrusive measurements by the hairpin resonator probe.
The experiments were conducted in a DC discharge tube with a diameter of 1.5 cm and a length of 7 cm. TMS diagnostics yielded electron number densities of about 5.9×1010cm-3, 2.8 ×1010cm-3 and 1.8 ×1010cm-3 at pressures of 0.2, 0.5 and 2.5 Torr, respectively. The corresponding densities measured with the hairpin resonator probe were 4.8×1010cm-3, 3.8 ×1010cm-3 and 2.6 ×1010cm-3. Discrepancies between the two techniques were within 30% and can be attributed mainly to inaccuracies in the sheath thickness estimation required the hairpin resonator probe results.
- Master of Science
- Aeronautics and Astronautics
- West Lafayette