Part I: An attempt was made to measure the impedance of an r.f. discharge by standing-wave methods. However, this was unsuccessful because the r.f. oscillator which was built for this purpose proved to have insufficient frequency stability. Part II: An r.f. discharge in helium was examined with a quartz prism spectrograph in order to deduce the temperature of its excited atoms and ions from the Doppler breadth of their spectrum lines. A new 150 Mc/s. oscillator supplied a 20 microsecond pulse of about 25 K.W. into the discharge fifty times per second, and a constricted discharge tube was used in order to concentrate the power in to a small volume of gas. The discharge was run at low pressure in order to reduce Stark broadening and was made part of a gas circulating system in order to avoid losses from 'clean-up'. The temperature drift of the spectrograph caused considerable difficulty, but the line breadths were corrected for this effect to a first approximation. At 0.03 mm. Hg. the breadth of the He I lines at 2723, 2764, 2829 A. corresponded to about 2,000°K. and that of the He II line at 2733 A. corresponded to 20,000°K.; this difference is attributed to Stark effect , but besides this it is possible that some contribution to the He I spectrum may have come from the relatively cool after glow. The relative intensities of the lines gave an excitation temperature of the order of 1,500°K. for He I and 4000°K. for He II (lines at 2733 and 3203 A .). Besides the possible contribution of the afterglow to He I, the most likely reason for these low excitation temperatures is that the electrons' velocity distribution was not Maxwellian but contained a greater proportion of low energy electrons because of inelastic collisions with the walls and secondary electron emission from the walls of the constriction. The relative intensity of the He I and He II spectra gave an equilibrium temperature of the order of 16,000°K.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:705547 |
| Date | January 1955 |
| Creators | Surplice, Norman Alexander |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.bham.ac.uk//id/eprint/7261/ |
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