# Air ionisation through insulated conductor

Imagine electric conductor,copper wire for example,that is fully coated with thin teflon coating and this coated wire is surrounded by air.

The classis high voltage air ionisation happens when the electrons start to escape naked non-insulated conductor and go into the air,its called corona discharge.

My question is,is it possible to cause ionisation of air by high voltage conductor that is fully coated by thin layer of strong insulator like teflon?

I think it my work in following way,near the insulated high voltage conductor,close to its surface there exist strong electric field that can accelerate positive ions or electrons,ofcourse,molecules and atoms of air are neutral,but its a fact that cosmic radiation,radon gas and ultraviolet light causes constant ionisation of air in the enviroment where we live,its very small amount but it exist and these small ionisation events,while invisible happen relatively often.

I think that maybe if one ionisation event happens near the insulated conductor where the electric field is strong,the field might be strong enough at that location to accelerate that electron to such degree it will cause ionisation by colliding with neutral air atom thus causing sort of avalanche where more electrons are ejected,they are accelerated and they ionise more atoms and it repeats and grows exponentialy.

Could all this happen like I described it? Could teflon insulated conductor really cause air ionisation without any current flowing from it into air?

Current isn't what you need for ionization to occur; what you need is a high electric field. An insulator will act as a dielectric, reducing the electric field seen by the air. But there will always be some nonzero field penetrating the insulation. It all comes down to the dielectric constant and thickness of the insulator, and the voltage on the conductor. If the insulator is not thick enough (or not dielectric enough), ionization will still occur. Likewise, no matter how thick the insulation is, there will always be a conductor voltage that can cause ionization.

Are you asking as a theoretical idea? Or do you have a sitution with thin-teflon coated wires and you observe something that could be air ionization, and you wonder whether this explanation is the correct one?

One thing that can happen with thin insulation is that it fails at spots. If it fails a little bit at one spot, enough to get a few electrons leaking through, they are likely to make it fail more. So you could get some localized spots that cause a lot of ionization, even while other areas don't do that.

Going from first principles, I wouldn't expect a high electric field from a high voltage. You have about the same number of protons and electrons, but the electrons on average are moving in one direction while the protons are still.

Assoming steady state, the moving electrons should create force in ratio $$(1-\frac{v^2}{c^2})\sqrt{1+\frac{v^2}{c^2}}$$ compared to the protons. So that's a positive field, but maybe not a large one. Or maybe working from first principles has led me astray.