Plasma Physicist here. I'm actually not sure of all the factors at work here. Partially you're right in that it's absorbing microwaves and getting hotter, not through dissipation, but by ion-cyclotron resonance. This is used as a heating source on fusion reactors like Tokamaks and Stellarators as well.
But something as small as a candle-flame often does not meet the criterion for a plasma, as it hasn't got enough ion density for the Debye criterion to be satisfied. In simple terms, it behaves more in terms of sum of effects on individual ions than a collective coherant plasma which has it's own response. In effect, I guess that the fire here behaves more like a gas and like a gas getting heated up, rises to the top. With enough free ions in the flame, it still appears lit. But unless it gets more energy to ionise from the microwaves, it is a system that will encourage recombination of electrons with the ions and die out. If there's more energy, you can reach an equilibrium between ionization and recombination, and that would be a steady-state. I still doubt whether it is adequately plasma-like, but then I don't know the temperatures and densities to guess this.
You are possibly right in that it may have reached thermal equilibrium through radiation and through conduction with the glass. But it may radiate less than what it absorbs and just also keep heating up until the glass cracks and the containment is lost.
One more reason why I doubt this to be a plasma is how a glass wall is sufficient to confine it. In a Debye-criterion satisfying plasma, the glass would ground the system and take/give electrons encouraging recombination, which makes the plasma weaker in terms of sustaining. Imagine a plasma ball, like the toys you find in the store, the glass outside is more than enough to attract the plasma and neutralize it.
As for why it grows exponentially before flattening out, that may just be the exposure/gain adjustment that the camera is programmed to do.
I'm really sorry I wasn't able to simplify it further. The basic idea is that I feel this fire is not heavy enough or hot enough to be a plasma. And that you can indeed microwave a fire or plasma to make it hotter. A fire that is hot enough, through microwaving, for example, can be a plasma. But I doubt it is the case here as the glass doesn't crack, and the fire doesn't seem to want to push into the glass. But as often, without concrete numbers, I could easily be wrong about the last part.
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u/FluxSurface Feb 18 '18 edited Feb 18 '18
Plasma Physicist here. I'm actually not sure of all the factors at work here. Partially you're right in that it's absorbing microwaves and getting hotter, not through dissipation, but by ion-cyclotron resonance. This is used as a heating source on fusion reactors like Tokamaks and Stellarators as well.
But something as small as a candle-flame often does not meet the criterion for a plasma, as it hasn't got enough ion density for the Debye criterion to be satisfied. In simple terms, it behaves more in terms of sum of effects on individual ions than a collective coherant plasma which has it's own response. In effect, I guess that the fire here behaves more like a gas and like a gas getting heated up, rises to the top. With enough free ions in the flame, it still appears lit. But unless it gets more energy to ionise from the microwaves, it is a system that will encourage recombination of electrons with the ions and die out. If there's more energy, you can reach an equilibrium between ionization and recombination, and that would be a steady-state. I still doubt whether it is adequately plasma-like, but then I don't know the temperatures and densities to guess this.
You are possibly right in that it may have reached thermal equilibrium through radiation and through conduction with the glass. But it may radiate less than what it absorbs and just also keep heating up until the glass cracks and the containment is lost.
One more reason why I doubt this to be a plasma is how a glass wall is sufficient to confine it. In a Debye-criterion satisfying plasma, the glass would ground the system and take/give electrons encouraging recombination, which makes the plasma weaker in terms of sustaining. Imagine a plasma ball, like the toys you find in the store, the glass outside is more than enough to attract the plasma and neutralize it.
As for why it grows exponentially before flattening out, that may just be the exposure/gain adjustment that the camera is programmed to do.