I admit that my comment about voltage and current is irrelevant as the current is given/ measured. But the resistive heating in the cathode wire is still only a few milliamps and this will not heat a conductor- even a modest conducort very much. Radiation and conduction through the stalk should easily keep up. The current to ground is actually through the plasma. That is why ythe current is zero till a voltage is reached where Pashin dischagre can occur..
In defense, if someone is thinking of 1000 Watts being consumed in a Fusor, they might compare it to a toster oven, running at 110 Volts and this will indeed get hot. with red glowing wires. But, at 11,000 volts the current is 100 times less and little resistive heating of the cathode wire will occur. Again the warmth of the wire cathode and the walls comes from the high voltage- high KE charged particles hitting surfaces. Power is power and heat is the final depository, but the intermediate processes are different.
Another comparison would be a 1.5 volt battery delivering 10 mA through a wire. I don't think anyone would think that the wire would get red hot. With a 10,000 V battery and appropiate resistance in the system, again the same 10 mA would flow through the cathode wire. with the same resistive heating. The expended energy in this case is dominated by voltage effects/ acceleration of charged particles. If this seems obtuse, consider a bullet. At 10 FPS (low voltage) it will not transfer much energy ,. But at 3,000 FPS (high voltage), even with the same bullet weight (Amps) the energy transfer is tremendous.. It is this voltage dependant energy that heats the cathode wire and the wall. Keep in mind that the KE flows both ways. Ions are attracted to and hit the cathode wire and heat it, the electrons are attracted by the grounded or relatively anode walls. The surface area of the wire is much less so it doesn't drain the generated heat as fast as the walls. That is why the cathode wire is red hot, while the walls are only warm..
Dan Tibbets
Silver inner grid
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Re: Silver inner grid
The power lost due to resistance in the wire of the grid is pretty close to nil. However the fact that silver is a very good reflector means it's a poor absorber and so, in turn, a poor emitter of heat.
You don't want a bright shiny grid: a black one will not get so hot, so you can push it harder before it melts.
You don't want a bright shiny grid: a black one will not get so hot, so you can push it harder before it melts.
- Richard Hull
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- Real name: Richard Hull
Re: Silver inner grid
All grids get hot.
All grids can melt.
No grid is capable of even getting warm due to electrical internal disappation.
There is no indestructable grid.
If the grid were made of ultra high resistance, pure nichrome, toaster heater wire. It would not heat one iota due to conduction losses in an amateur fusor. Let all discussions related to grid dissapation of electrical energy die here.
Tungsten is the best material that can be easily acquired and is very high resistance electrically, but as above, zero electrical dissapation.
The desired cross section of grid wire is related to its ability to heat due to particle bombardment at a given input power and survive same without melting.
No one has tested a very large cross section pure silver grid as an integral part of a large diameter, cast, pure silver stalk. The heat conductivity of silver is superb and near the top of heat conductive elements. A large 10 ounce grid, stalk and top electrode would take off a lot of heat, but its rather low melting temperature and sputtering might prove to be not worth the effort.
I'll stick with Tungsten.
Richard Hull
All grids can melt.
No grid is capable of even getting warm due to electrical internal disappation.
There is no indestructable grid.
If the grid were made of ultra high resistance, pure nichrome, toaster heater wire. It would not heat one iota due to conduction losses in an amateur fusor. Let all discussions related to grid dissapation of electrical energy die here.
Tungsten is the best material that can be easily acquired and is very high resistance electrically, but as above, zero electrical dissapation.
The desired cross section of grid wire is related to its ability to heat due to particle bombardment at a given input power and survive same without melting.
No one has tested a very large cross section pure silver grid as an integral part of a large diameter, cast, pure silver stalk. The heat conductivity of silver is superb and near the top of heat conductive elements. A large 10 ounce grid, stalk and top electrode would take off a lot of heat, but its rather low melting temperature and sputtering might prove to be not worth the effort.
I'll stick with Tungsten.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment