There are a many alternate light and dark regions present in the cathode ray tube, as the pressure is reduced to minimum, like Crooke's dark space,negative glow, Faraday's dark space and at very low pressures even the positive column is present in the form of striations. I understand the reason for Crookes's dark space that there is very high potential near the cathode, due to which electrons escape faster than the heavy positive ions and there is no release of light as there is no combination of positive ions and electrons, but what are the reasons for other dark and light spaces? And why are they alternate?
Regularly spaced light and dark bands far from either anode suggests a simple matter of the electrons picking up the kinetic energy necessary to excite the neutral atoms, giving most of it up when they do so, and then re-accelerating down the tube.
We would expect a couple of diagnostic features:
- The bands nearer the cathode to be more sharply defined and those far from the cathode to become less and less distinct.
- The bands would blur and then disappear as the pressure was reduced to the point that the mean free path of the electrons became comparable to the distance over which the excitation energy was obtained starting from rest.
If this is the case it would be closely related to the phenomena observed in the Frank-Hertz experiment.