An apparatus has been developed for the measurement of the drift velocities of electrons in compressed gases. Velocities have been measured in nitrogen, argon and carbon dioxide at pressures from approximately 3 atm up to pressures of 70, 100 and 17 atm respectively. The measurements have established that, to within the experimental error, the electron drift velocities in nitrogen and argon are independent of gas density and depend only on the ratio of the the electric field to gas particle density (E/N) up to the highest pressure investigated. In carbon dioxide, at pressures of approximately 10 atm and above, it has been found that the behaviour of electrons appears to be fundamentally different from their behaviour at low pressures; in particular, the drift velocity was found to decrease with increasing pressure for a fixed value of the ratio E/N, and a slow decay of current occurred at the end of the electron pulses.
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