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So... all you plasma physicists, explain this.

Posted: Sat Jul 11, 2009 5:54 pm
by Robthebob

Posted: Sat Jul 11, 2009 9:03 pm
by Tom Ligon
Explain that? Simple. Guys without a feminine influence.

If you try that at home, a couple of things will happen. First, you many damage your microwave oven (insufficient load in the cavity plus smoke deposits and a bad smell inside). Second, if married, your significant other will cut your delicate parts off and hang them on the wall for messing with her microwave oven.

Flames are at least partly ionized and are electrically conductive. There's an old trick used to make the earliest flash photographs of bullet shock waves in which a candle flame acted as a plasma switch to fire a spark gap from a Leyden jar. See Toepler, Mach, and C. V. Boys mentioned together regarding photographing bullets. ... images.pdf Boys, C. V., “On electric spark photographs; or, photography of flying bullets, etc., by the
light of the electric spark,” Nature 47 1219:440-446 (1893)

We used to do far more unspeakable things to microwave ovens at EMC2, but we always used retired junkers.

Posted: Sun Jul 12, 2009 3:26 pm
by Torulf2
I made that with my microwave oven. I had a pyrex flask and a steal tread loop.
The microwaves induce a current in the plasma, making more plasma.

Posted: Mon Jul 13, 2009 9:30 am
by kcdodd
I have done this as well. However, the reason is not the flame on the toothpick. What happens is as the toothpick burns it becomes carbonized and slightly conductive. It then acts as an 1/4 (or 1/2) wave antenna to the microwaves (12cm). This builds up massive voltage and produce high temp sparks which then act as the conductive plasma, which also absorbs the microwaves. It's easier to cut off pieces of pencil at 1/4 (or 1/2) wavelength to produces the plasmas (b/c of the graphite).

Posted: Mon Jul 13, 2009 3:59 pm
by Tom Ligon
That makes sense. The stub of the magnetron is a 1/4 wave radiator, about an inch and a quarter long.

I wonder if a frame by frame examination of the fireballs would reveal anything about the distribution of microwave energy in the cavity, though. The microwaves are produced in pulses at 60 Hz (due to the unfiltered voltage doubler typically powering them. A camera with an NTSC scan rate might synch up with this if you are lucky.