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In an electron beam, is the light region under pressure below atmospheric pressure?

Electron beam

Motivation of my question: In the cathode ray tube, the cathode ray (electron beam) becomes luminous and visible because there is low pressure inside the tube. If the internal pressure drops too low, the light beam disappears. If you try to simulate the same electron beam at atmospheric pressure, using the same voltage, you cannot obtain the light beam. So, by analogy, I assume that the visible electron beam is only possible under a specific air pressure condition. Is my reasoning correct?

If it is true that the electron beam becomes luminous under specific conditions of air pressure, what causes air to reduce the pressure in the electron beam? Is it the ionization of air?

Sorry if my question seems too basic. Or if it is elaborated in the wrong way. I just wanted to know if an electron beam affects atmospheric pressure through ionization.

Kabir Costa
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In direct answer to your question, the electron beam does not materially affect atmospheric pressure through ionization.

A sufficiently energetic electron beam will produce light in atmospheric air.

This video might help: https://www.youtube.com/watch?v=m3oonk1wnHY

The picture you shared looks like it might be a "cold plasma jet"; such a thing uses argon and a high frequency AC supply to generate a cold electron plasma.

chrism2671
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  • Olá @crisma2671, first of all, thank you for the answer. – Kabir Costa Nov 22 '20 at 19:58
  • This specific image is from this video: https://youtu.be/C0Fry6ktu4w?t=141, which are electrical discharges directly into atmospheric air. I believed that there was a correlation between beam brightness and atmospheric pressure. Since at atmospheric pressure, much more voltage is needed to generate a light beam than if it is at low pressure. – Kabir Costa Nov 22 '20 at 20:04
  • So in answer to your question, the glow in the air is coming from ionisation, but the processes are different.

    Any substance (including air) will be ionised if you hit it with a strong enough field/energy.

    What you're seeing in this video is https://en.wikipedia.org/wiki/Electrical_breakdown - which means there's a voltage of > 3kV/cm gap.

    In the low pressure tube, what you're seeing is 'avalanche ionisation': https://en.wikipedia.org/wiki/Electron_avalanche

     – chrism2671 Nov 23 '20 at 15:38