Initial conditions of electrons in the Ives-Stillwell experiment

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I've never been able to find the answer to this question - maybe someone on here knows the answer. What were the initial conditions of the ELECTRONS in the experiment?

There seems to be the implicit assumption that only the positive ions' state of motion has an effect on the photons being emitted. I recognize that the ions are orders of magnitude more massive than the electrons, and thus their trajectories would be essentially unaffected. But aren't the photons emitted by the JOINT actions of both positive and negative charges? And how did the electrons get past the accelerating grid into the recombination chamber?

Could the answer be that the initial conditions of the electrons are "random". And thus the "net" directed activity be that of the positive ions?
 
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Ok.

Does anyone know how I can find a copy of their original paper? There might be some clues in it.
 
The wikipedia provides references (and links) to two different papers by Ives and Stillwell.
 
I finally got a copy of the original paper. And the answer is that the spectral line they studied was the H-Beta blue-green(?), which is an INTERNAL transition. So the initial conditions of the electrons were the same as that of the nucleus to a very high degree of approximation.

Also, they had to significantly modify their "canal ray" tube to get discrete spectral lines. They didn't say specifically how, but I am guessing it was drastically lowering the gas pressure - to stop the impacts, mixing, random velocities and Doppler shifts that would smear the lines.