Scattering of electrons by ions and the mobility of electrons in a Caesium discharge

The mobilities of electrons in the positive column of a caesium discharge are derived from measurements of the electrical gradient and the electron tempera- ture and concentration. The value of the caesium atom cross section, estimated from the mobilities at small electron concentrations, is 3.3 x 10 -H cm 2 for electron energies of about 0.33 volt. The cross section apparently increases linearly with the concentrations of ions in the discharge. The variation is found to be due to the scattering of the electrons by ions. The value of the ion cross section can be evaluated from the rate of variation; it is 75X10 -14 cm 2 for 0.33 = volt electrons.