The localisation of the discharge in ordinary and canal-ray tubes
The radial distribution of the electric current on the cathodic surface has been investigated by observing the current distribution between the three sectors of a cathode in the case of the discharge in the gases oxygen, hydrogen, nitrogen and air for different voltages, discharge currents and lengths of the cathode dark space, under conditions of ordinary and canal-ray discharge.
There is in general a concentration of the current in the centre for the range of voltages used, in the case of the different gases.
For a given gas the localisation (or this concentration of the discharge) is independent of the voltage, the discharge current, and is determined only by the length of the cathode dark space (D.S.L.).
The localisation increases with the length of the cathode dark space and reaches a stationary value for very high lengths (of the order of 5 cms.).
Under the conditions of canal-ray discharge, the localisation is only slightly different from that obtained with an ordinary tube in the case of hydrogen. There is no such difference in the case of air. Under these conditions the radial distribution of the current-density is the same for the different gases for the same value of the D.S.L.