Mobility of the Ions in the Corona Discharge

The mobility of the ions generated in the d.c. corona discharge have been directly measured. Gas, moving with a uniform velocity, was ionized in a cylindrical corona tube and then passed into an ion chamber consisting of a hollow cylinder with electrodes along the axis. The ion current to the last electrode, when plotted as a function of the cylinder potential, exhibited maxima which indicated the presence of groups of ions. Calculation revealed a large number of groups whose mobilities, for oxygen, nitrogen, and carbon dioxide, were all less than.716 cm/sec per volt/cm, ranging down to ${10}^{-5\mathrm{}}$ cm/sec per volt/cm. Nearly all mobilities were found below ${10}^{-2\mathrm{}}$, the ions apparently being generated in equal numbers, except now and then a greater number of a certain mobility were formed. The fact that the ions all possessed small mobilities seems to indicate that J. Kunz made the correct assumptions when he calculated the average value from the experimental determination of the pressure increase in the d.c. corona.