Induce current in air?

[michan]

Hi all,

So I'm currently taking a physics subject at uni on electrodynamics and a lot of it i have noticed can be related to processes in nuclear fusion. Eg; a method of heating up plasma where they induce a current in the plasma itself to heat it up.

Part 1 of question)
I was wondering if this same process would work on air at atmospheric conditions since the gasses they heat up in fusion reactors are at really low pressures.

Part 2 of question)
If it would work on just plain old air and a plasma was produced id imagine the emf produced by the coil driving the induction would be extremely large. If you were to place a sort of Faraday cage around the entire set up would that cage end up 'coupling' to the coil or somehow end up drawing most of the power away from the induction taking place in the plasma?

Sorry about the explanations, its hard to communicate what I'm trying to imagine but if you can imagine the situation, any contribution would be really interesting. Thanks.

 

[BobK]

Yes. It is called a spark. Or, on a larger scale, lightning.

Bob

 

[michan]

Yes. It is called a spark. Or, on a larger scale, lightning.

Bob

Hahaha ok I should have specified, I mean via induction in the same way an induction Heater or induction furnace works to induce an eddy current in the metal workpiece. I guess I'm trying to say can you make eddy currents in air using a similar set up to an induction furnace. Like a coil with a high frequency Ac current flowing through it to create the changing magnetic field powerful enough to create such an eddy current in air.

 

[hevans1944]

There is a device called a plasma torch that ionizes air by means of an intense RF field inside an open coil. Air is blown through the center of the coil, becomes ionized to a plasma state as a result of absorbing RF energy, and exits the coil as a hot gas suitable for wherever you need to use a hot gas. The technology is old. I first encountered it when it was a feature article in an issue of Electronics magazine in the 1960s. I wanted to build one, but didn't have the requisite high-power vacuum tube. Turns out there are easier ways to produce a plasma jet of air, including a massive current discharge once you obtain the initial ionization required to sustain a high current.

Plasma discharges are fun things to play with. The common neon tube lamp contains an ionized plasma, as do fluorescent tube lamps. Once you obtain a sustained spark in air, it is relatively easy to dump a few thousand amperes of current through it to create massive plasma discharges. Depending on electrode geometry, the voltage after ignition is not very large. Some folks wind low-voltage secondaries on microwave oven transformers (MOTs) to obtain hundreds of amperes of current. Larger transformers will yield more current of course. Have fun!

 

[davenn]

Like a coil with a high frequency Ac current flowing through it to create the changing magnetic field powerful enough to create such an eddy current in air.

air is an insulator, so generating eddy currents or any current in it isn't going to happen
small sparks up to huge lightning sparks only happen because of dielectric voltage breakdown of the air
for air the breakdown voltage is approx 30,000V (30kV) / cm ( centimetre)
The air needs to be ionised for current to flow


Dave

 

[michan]

There is a device called a plasma torch that ionizes air by means of an intense RF field inside an open coil. Air is blown through the center of the coil, becomes ionized to a plasma state as a result of absorbing RF energy, and exits the coil as a hot gas suitable for wherever you need to use a hot gas. The technology is old. I first encountered it when it was a feature article in an issue of Electronics magazine in the 1960s. I wanted to build one, but didn't have the requisite high-power vacuum tube. Turns out there are easier ways to produce a plasma jet of air, including a massive current discharge once you obtain the initial ionization required to sustain a high current.

Ah interesting! Do you have any links/books or names of these phenomena where plasma can be produced and sustained in a jet of air other than the induced method that I was originally asking about?

 

[hevans1944]

Ah interesting! Do you have any links/books or names of these phenomena where plasma can be produced and sustained in a jet of air other than the induced method that I was originally asking about?

Gee, do you want me to read them out loud to you? Did you even visit the link I posted? Start there and find others yourself. Make Google your best friend for this. Also, read page 10 of this PDF link.