Ion Mobilities in Helium, Neon, and Argon

Measurements of the electron density as a function of time during the decay period of pulsed plasmas produced in helium, neon, and argon are reported. The values of the mobilities of positive ions in their parent gas, calculated from the rate of electron loss by ambipolar diffusion, are compared with those measured with the ion-transit-time methods. The values, consistent with data obtained with these two different measuring techniques, are ${\ensuremath{\mu}}_{0}({\mathrm{He}}^{+})=10.7$, ${\ensuremath{\mu}}_{0}({{\mathrm{He}}_{2}}^{+})=16.2$, ${\ensuremath{\mu}}_{0}({\mathrm{Ne}}^{+})=4.1$, ${\ensuremath{\mu}}_{0}({{\mathrm{Ne}}_{2}}^{+})=6.5$, ${\ensuremath{\mu}}_{0}({\mathrm{Ar}}^{+})=1.6$, and ${\ensuremath{\mu}}_{0}({{\mathrm{Ar}}_{2}}^{+})=1.9$ ${\mathrm{cm}}^{2}$/V sec. The dependence on gas pressure of the efficiency of the cataphoretic segregation of neon impurity atoms in helium is demonstrated and explained.