An analysis of ion-acoustic oscillations in a plasma column



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An analysis is made of some experimental work done on ion-acoustic oscillations in a plasma. In an experiment conducted by I. Alexeff and R. V. Neidigh, the electron temperatures are calculated by measuring the frequencies of the ion-acoustic oscillations. This is done for a number of various gases. The electron pressure is also measured. In an experiment done by J. R. McNally and M. R. Skidmore, the ion temperatures are measured in a similar experimental set-up. The equation used by Alexeff and Neidigh for the determination of temperature is developed and discussed. The choice of a value for the adiabatic electron gas compression coefficient is discussed. The value of 5/3 is chosen in opposition to the author's choice of 3. This is justified by showing that in each case the electron-electron collision frequency is greater than the oscillation frequency. That is, the electron gas is thermalized. The measurement of electron pressure is discussed and it is shown that an equation of state does indeed exist for the electron gas. An equation is devised relating the ion temperature, the electron temperature, and the ion-electron recombination coefficient. Although this equation does not seem feasible for the determination of ion temperature due to its sensitivity to experimental error, it does turn out to be useful in determining the recombination coefficient if the ion temperature is already known.