Studies radio-frequency gas discharge

[摘要] 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.

[发布机构] University:University of Birmingham;Department:Department of Electron Physics

[关键词] Q Science;QC Physics