Exploring the Molecular Mechanisms of Electrical Breakdown in Air

[Andy Kay]

I have noted three different phenomena due to high electric fields in air.

1. When I run a ten-stage voltage multiplier I get sparking and crackling.

2. When I run the multiplier but current limit the output with ten 720k resistors in series, I get a violet arc that is sometimes smooth and quiet and sometimes jagged and hissy.

3. When I run a Jacob's Ladder from a flyback transformer (driver draws around 5A) I get a whitish flame-like arc.

Can anyone enlighten me as to what is going on at the molecular level to give these three different phenomena?

Thanks for reading.

 

[NascentOxygen]

Hi Andy Kay.

In my home DIY experiments while at high school, I generated ozone by "a silent electric discharge in air". This involved two parallel electrodes in air, but with a length of glass tubing over one of them. This produced a purple glow inside the tubing, but a complete absence of snappy blue sparks. I'd say the mechanism is one where electrons are stripped off oxygen molecules by the high electric field but the high path impedance prevents the establishment of a continuous conductive path which would discharge the high tension source. Operation was characterised by the unmistakable penetrative smell of ozone (a gas you don't wish to breathe much of). This may be the explanation for your purple glow in (2), ionization but on a limited extent that doesn't support continuous conduction.

 

[Andy Kay]

Hi Andy Kay.

In my home DIY experiments while at high school, I generated ozone by "a silent electric discharge in air". This involved two parallel electrodes in air, but with a length of glass tubing over one of them. This produced a purple glow inside the tubing, but a complete absence of snappy blue sparks. I'd say the mechanism is one where electrons are stripped off oxygen molecules by the high electric field but the high path impedance prevents the establishment of a continuous conductive path which would discharge the high tension source. Operation was characterised by the unmistakable penetrative smell of ozone (a gas you don't wish to breathe much of). This may be the explanation for your purple glow in (2), ionization but on a limited extent that doesn't support continuous conduction.

Thank you for your reply. I think the salient comment was "does not support continuous conduction" -- this is helpful. I'm guessing, then, that the voltage multiplier spark consists of continuous conduction for as long as the capacitor stack can sustain it before needing time to recharge. Also that the current-limited voltage multiplier is, as you say, limited ionization without continuous conduction. And finally that the Jacob's Ladder effect is continuous conduction that does not need time for recharging. That would seem to make sense. Thank you for this and please correct me if I am still getting it wrong.