The Langmuir Paradox in Discharge Plasmas

Abstract

IN a recent communication, Gabor, Ash and Dracott have described the detection of oscillations in a positive ion sheath separating a section of wall from the positive column plasma of a low-pressure arc in mercury vapour¹. The oscillations were studied by passing a pencil of cathode rays through the sheath, and were found to have two main components, one with frequencies of up to about 100 kc./s., and the other with frequencies of the order of 100 Mc./s. We have been investigating the fluctuations of similar discharges by the alternative method of withdrawing oscillatory energy through the main electrodes (anode, cathode) and probes to tuned detectors, and have obtained what appear to be comparable experimental results. Our method does not permit of observation over individual periods of a few hundredths of a microsecond, as does Gabor's, but yields a long-time Fourier analysis of the fluctuations.