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Striations in cathode ray discharge

  1. Jan 5, 2016 #1
    image.jpg What causes these striations? How does the voltage and pressure of the discharge affect the size, color, number, and spacing of the striations? I have produced a discharge with striations with fairly low voltage (under 15kv) and pressure 10 - 100pa, and the striations are very thin, compact, and numerous. Most of the striations I see online are very thick and few in number. This is also a noisy dc supply so that may affect things as well.

    I am having a difficult time finding information on the process that causes this.
  2. jcsd
  3. Jan 9, 2016 #2


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    I think it might be audio frequency oscillation in the system.
  4. Jan 9, 2016 #3
    This is a genuine effect caused by ionisation of the low pressure gas. Electrons are accelerated from the cathode (the upper electrode) the 'dark spaces' are where electrons are being accelerated, they collide with gas molecules which are ionised and recombination results in the glow. The dark spaces are known as 'Crookes dark spaces'...the scientist associated with these experiments. At very low pressure electrons from the cathode are able to reach the glass walls of the tube and fluorescence occurs in the glass..this is the basis of fluorescent light tubes (they are coated to increase fluorescence)
    Last edited: Jan 9, 2016
  5. Jan 9, 2016 #4


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    I think you will find that, as the pressure is reduced, the spacing of the striations will increase - because the mean free path increases.
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