Here's a kick-off question; why have a vacuum for fusion?
Posted: Mon Aug 30, 2010 4:28 pm
So I'm trying, here, to get the 'theory' section going with a, somewhat, historic question to stimulate a debate: Can you 'do' electric-fusion at atmospheric pressure, and if not, then why not?
[My glossary of 'electric-fusion' is any situation where ions gain fusible energy by acceleration in an electric field, rather than thermal energy in an ensemble of ions.]
As a naïve construction, imagine we just shrink a regular Farnsworth fusor by a linear 100x, but otherwise do all the same things as would be done in a vacuum. Why would the outcome differ to its vacuum brother with a 10^6 bigger volume at 10^-6 density?
There are plenty of plasmas at atmospheric pressure. Here is an alternative; what happens if you leak deuterium out of a fine metal tip held to a substantially negative voltage such that a coronal discharge forms? Deuterium ions formed at the edge of the corona would accelerate back to the tip, causing much the same situation as in an evacuated fusor.
I mentioned that this was a historic point and I say this because of a chap called Lidsky. Lawrence Lidsky was an assistant director of MIT fusion centre when he published an article in 1983 in which he blasted fusion research. One of the main gripes he used to deliver to his students [apparently] was the appauling power density of fusion. This is something I have commented on several times vis-a-vis the Sun, on fusor.net. Those who say they seek to reproduce the Sun are misleading at best because the Sun produces, volume-per-volume, 1/1000th of the heat output of your own warm, mammalian body. The modern tokamak collossi are figured to run at about 0.5W/cc. Lidsky's point was that the size and, thus, complexity to produce useful power outputs will never, ever, compare with fission when you can breed fuel from U238 and thorium.
Prior to Lidsky's 'unappreciated' output of critique [for which he was quietly removed from his post] he discussed the pathetic power densities available to controlled fusion with his students and it lead him to make the statement (reported as) "If there's a leaf left on a tree to burn, you won't want to build this" for each fusion method available. I believe one of his research aims was to look for ways to run fusion experiments at higher pressures.
The issue of power density is one I am adversely sensitive to, also. As you may or may not know, I have filed a patent for a 'new approach' to electric fusion which involves the active recovery of scattered ions. More on this later, but the point is that the device I have patented will, I calculate, also have a pretty miserable power output. In my case, I calculate that a device some 2m across would generate about 1kW. Volume-per-volume, it's probably much as tokamaks are, but you can see the issue - if we want it to power houses then you might conceive of burying one under each house, but is that really more satisfactory than simply sticking solar panels all over the roof space?
So my maiden post, here, asks a few questions of the audience..;
a) can we make an atmospheric-pressure fusion device?
b) if not, why, and are we expecting from [vacuum-based] terrestrial fusion to get beyond a 0.5W/cc limit?
c) was Lidsky right? Is it better to burn what we've got before wasting time on fusion power?
d) why go to the trouble of inventing fusion power if it is going to take up more space that a load of solar panels of the same power output/space?
...and make statements;
e) I have an idea for electric fusion that I'll be running though here on this forum, in due course, and the maths seems to work out to suggest there might be something in it, but I don't really see it as useful energy at any moment for several generations to come because all fusion looks a bit 'thin' on the energy-producing front due to the minuscule specific power outputs, so I'm in this just to see if I can't beat these generations of scientists to a better approach than the still-unproven magnetic confinement idea.
f) it's looking like the best means to make use of fusion power is to round up 2x10^30 kg of H2, put it all in a 400,000 mile radius bubble 90 million miles away, and suck up the incandescent heat off of it!
[My glossary of 'electric-fusion' is any situation where ions gain fusible energy by acceleration in an electric field, rather than thermal energy in an ensemble of ions.]
As a naïve construction, imagine we just shrink a regular Farnsworth fusor by a linear 100x, but otherwise do all the same things as would be done in a vacuum. Why would the outcome differ to its vacuum brother with a 10^6 bigger volume at 10^-6 density?
There are plenty of plasmas at atmospheric pressure. Here is an alternative; what happens if you leak deuterium out of a fine metal tip held to a substantially negative voltage such that a coronal discharge forms? Deuterium ions formed at the edge of the corona would accelerate back to the tip, causing much the same situation as in an evacuated fusor.
I mentioned that this was a historic point and I say this because of a chap called Lidsky. Lawrence Lidsky was an assistant director of MIT fusion centre when he published an article in 1983 in which he blasted fusion research. One of the main gripes he used to deliver to his students [apparently] was the appauling power density of fusion. This is something I have commented on several times vis-a-vis the Sun, on fusor.net. Those who say they seek to reproduce the Sun are misleading at best because the Sun produces, volume-per-volume, 1/1000th of the heat output of your own warm, mammalian body. The modern tokamak collossi are figured to run at about 0.5W/cc. Lidsky's point was that the size and, thus, complexity to produce useful power outputs will never, ever, compare with fission when you can breed fuel from U238 and thorium.
Prior to Lidsky's 'unappreciated' output of critique [for which he was quietly removed from his post] he discussed the pathetic power densities available to controlled fusion with his students and it lead him to make the statement (reported as) "If there's a leaf left on a tree to burn, you won't want to build this" for each fusion method available. I believe one of his research aims was to look for ways to run fusion experiments at higher pressures.
The issue of power density is one I am adversely sensitive to, also. As you may or may not know, I have filed a patent for a 'new approach' to electric fusion which involves the active recovery of scattered ions. More on this later, but the point is that the device I have patented will, I calculate, also have a pretty miserable power output. In my case, I calculate that a device some 2m across would generate about 1kW. Volume-per-volume, it's probably much as tokamaks are, but you can see the issue - if we want it to power houses then you might conceive of burying one under each house, but is that really more satisfactory than simply sticking solar panels all over the roof space?
So my maiden post, here, asks a few questions of the audience..;
a) can we make an atmospheric-pressure fusion device?
b) if not, why, and are we expecting from [vacuum-based] terrestrial fusion to get beyond a 0.5W/cc limit?
c) was Lidsky right? Is it better to burn what we've got before wasting time on fusion power?
d) why go to the trouble of inventing fusion power if it is going to take up more space that a load of solar panels of the same power output/space?
...and make statements;
e) I have an idea for electric fusion that I'll be running though here on this forum, in due course, and the maths seems to work out to suggest there might be something in it, but I don't really see it as useful energy at any moment for several generations to come because all fusion looks a bit 'thin' on the energy-producing front due to the minuscule specific power outputs, so I'm in this just to see if I can't beat these generations of scientists to a better approach than the still-unproven magnetic confinement idea.
f) it's looking like the best means to make use of fusion power is to round up 2x10^30 kg of H2, put it all in a 400,000 mile radius bubble 90 million miles away, and suck up the incandescent heat off of it!