I'm not sure how to categorize this, but it is not directly related to LENR, although it might be possible related to some claims using plasma discharge apparatuses. So in the off-topic section this goes for now.
In the past couple days I came across an unusual (i.e. not often encountered) heating phenomenon while experimenting with atmospheric glow plasma discharges. There is probably nothing out of the ordinary occurring here, but it shows how an apparently low power could heat up small amounts of material to surprisingly high temperatures. Here is one of the several videos I made of the process.
Description: a small section of nickel-wound guitar steel wire was previously melted into a ball with an approximately 750V plasma discharge. This video shows a reheat attempt. A 15.4 kOhm resistor in series with the anode acted as a ballast. The screwdriver acted the anode (+), the bottom steel plate acted as the cathode (−).
As the NiFe ball (of about 1 mm diameter) attached itself to the cathode, it started glowing brightly in the process (emitting numerous sparks in the first attempt). Temperature got high enough to cause the steel surface beneath the ball to blacken. The screwdriver/anode did not receive any substantial melting damage.
It appears that the heated material at the cathode heats up to its melting point, but no more than that. Nickel melts at 1453 °C; mild steel depends on the composition but should be above 1300 °C. The beginning of the video also shows that if the ball is at the anode no significant heating will occur.
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A similar heating process can be observed with similar amounts of mild steel or copper, but not elemental aluminium (e.g. foil), at least directly/easily. The NiFe material shines brighter than copper, but not as much as aluminium when conditions are right (I think that comes from aluminum oxide, which becomes conductive at a high enough temperature).
From a few measurements I attempted, it is plausible that the impedance of the plasma region is in the order of 8 kOhm, which means that the total circuit resistance is about 23.4 kOhm. The voltage drop at the ballast resistor while a discharge is occurring is about 475−550V depending on conditions. One could work out roughly 23W total circuit power, with 15W dissipated at the ballast resistor and 8W at the heated material/plasma region.
I think what could be happening here is that while 8 watts is not a very large power, it might be concentrated on a very thin region which can heat the material up to its melting point. However this occurs only when the heated material is at the cathode and does not dissipate heat efficiently. This sounds kind of obvious, but a less obvious factor is that such heated material will start producing thermionic emission possibly in a positive feedback loop with temperature.
I'm not entirely certain of the processes involved though, so I look forward to reading others' suggestions.