E Field at a Glow Discharge Tube Cathode

[Dan Jenson]

I am trying to understand the "strong" negative E field in the Aston Dark Space in the thin region close to the cathode or else even the cathode surface.

See the diagram at:

http://www.glow-discharge.com/?Physical_background:Glow_Discharges

My question regards the "Electrical Field E" graph which shows a strong level at the cathode, but in the lower description of the AstonDark Space is mentioned, "The electron density and energy is too low to efficiently excite the gas, it consequently appears dark".

Does this mean that the electron density and energy here is generally low ? How do we identify the strong electric field then ?

On my set up the cathode is grounded. Earth ground while containing an infinite abundance of electrons does not give a strong electric field.Maybe if the atoms were polarized then a positive or negative field could emerge. Or what ? How should I understand this ?

I should add that there exists some circuit impedence maybe in the wiring between my plasma cathode and ground and this may allow for field conditions to form at the cathode without direct Earth reference grounding out the effect, but now returning to my question, wht is this strong E field ?

My particular set up is known for producing a strong E field emanating from the cathode but I am not understanding it.

Thanks, dj

 

[eljose79]

Hello dj,

Thank you for your question. The strong negative E field in the Aston Dark Space is a result of the presence of a cathode in the plasma. When a cathode is present, it emits electrons which are accelerated towards the anode by the electric field. This creates a region of high electron density and energy close to the cathode, resulting in a strong negative E field.

In the lower description of the Aston Dark Space, it is mentioned that the electron density and energy is too low to efficiently excite the gas. This means that even though there is a strong negative E field present, the electron density and energy are not high enough to cause the gas to glow or emit light. This is why the Aston Dark Space appears dark.

The fact that your cathode is grounded does not necessarily mean that the electric field is weak. The strength of the electric field is determined by the potential difference between the cathode and anode, not the grounding of the cathode. If the atoms in the gas were polarized, it could result in a stronger electric field, but this is not the main factor in the strength of the electric field in the Aston Dark Space.

It is possible that the circuit impedence in your setup is allowing for the formation of a strong E field at the cathode, even with grounding. However, without more information about your specific setup, it is difficult to determine the exact cause of the strong E field.

In summary, the strong negative E field in the Aston Dark Space is a result of the presence of a cathode in the plasma. The electron density and energy in this region may be low, but the electric field is still strong due to the potential difference between the cathode and anode. The specific factors contributing to the strength of the E field in your setup may require further investigation. I hope this helps clarify your understanding of the phenomenon.