Hello. I come here with a little trepidation after seeing that perhaps some of the more experienced folks here might be tired of hearing basic questions from those interested in fusors. I am new to this area (like last 24hr new) but I have been playing with high voltage stuff for years. Made things from Tesla coils to lifters and some of my own unique variants thereof. I have a formal chemistry background which was also reinforced with some engineering and physics.
I am looking to not just build a fusor (fun looking project) but maybe apply some ideas to improving it. I noticed a lot of designs rely on fairly primative electrodes which cause conductive loss and that most folks have no serious ideas on how to harness the power except through "maybe a turbine". I think once I get one working I would like to improve on a few aspects like these deficiencies. Off the top of my head I can think of a few things that might be better than an eggbeater but until I actually build and test it I should hold off announcing these ideas.
Anyway, I am new here. Plan to make something even if all I do is have fun. I look forward to discussing ideas with your forum.
Daniel Villageliu
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Daniel Villageliu
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- Real name: Daniel Villageliu
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prestonbarrows
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Re: Daniel Villageliu
Hi Dan
To first order, the biggest issue with IEC devices is that it is much more likely for an ion to smack into something and give up its energy benignly rather than produce useful fusion. This is mostly because the fusion cross section is always quite small. Each time nuclei interact, simple scattering is typically 3 or more orders of magnitude more likely than fusion. The two main categories of interactions are those in the vacuum and those in the bulk grid/chamber material. The former tend to be inelastic collisions where the original energetic ion transfers some of its energy into kinetic and/or ionization potential energy of some random neutral atom. The latter tends to produce waste heat as the original energetic ion transfers all of its energy into thermal motion of the metal surfaces in the system.
Assuming a constant pressure throughout the system, the number of interactions per distance traveled by an ion is relatively constant. So if we want an efficient system, we need the average ion to travel some minimum distance ( and interact with some minimum number of other nuclei while maintaining its high energy) before being absorbed into the bulk of the walls so that most of them fuse before being wasted.
You can come up with the rough distance traveled by a given ion algebraically by using the transparency of the grid. Say your grid is 99% transparent, that is to say that the wire occludes 1% of the solid angle of a spherical surface. The chance an ion passes through once (one diameter) is 0.99, the chance the ion passes through twice (two diameters) is 0.99*0.99 and so on.
If you run a thought experiment following a single ion, you can see that you either need the grid to be extremely transparent such that many millions of oscillations are allowed before the average ion impacts the grid; or you need an extraordinarily large grid such that an ion travels the required distance in only a few recirculations. Both ends of the spectrum are not very practical. Either the grid needs to be so fine that you cant physically build it (and/or it burns itself up), or the grid needs to be so big it would be a sizable fraction of the diameter or Earth.
If you don't want to take my word, look up the literature from University of Wisconsin, Japanese universities which currently have the most active IEC programs in terms of theory and experimental systems. It is well accepted by the field that IEC will never produce net gains though they are useful for other applications.
For your second point, speaking in broad strokes, fusion power would be captured either directly by energetic charged products traveling though an electric potential, or photoelectrically converting photons with an 'onion shell' geometry of plates, or thermally catching neutral products and running them through a steam cycle. Generally, those three options are listed in terms of the most efficient to the least efficient. Which approach is most reasonable depends on the type of fuel you are using and a large number of physics/engineering constraints.
tl;dr fusion is easy, energy efficient fusion is stupidly difficult.
Edited to fix dumb math error, thanks Tom.
To first order, the biggest issue with IEC devices is that it is much more likely for an ion to smack into something and give up its energy benignly rather than produce useful fusion. This is mostly because the fusion cross section is always quite small. Each time nuclei interact, simple scattering is typically 3 or more orders of magnitude more likely than fusion. The two main categories of interactions are those in the vacuum and those in the bulk grid/chamber material. The former tend to be inelastic collisions where the original energetic ion transfers some of its energy into kinetic and/or ionization potential energy of some random neutral atom. The latter tends to produce waste heat as the original energetic ion transfers all of its energy into thermal motion of the metal surfaces in the system.
Assuming a constant pressure throughout the system, the number of interactions per distance traveled by an ion is relatively constant. So if we want an efficient system, we need the average ion to travel some minimum distance ( and interact with some minimum number of other nuclei while maintaining its high energy) before being absorbed into the bulk of the walls so that most of them fuse before being wasted.
You can come up with the rough distance traveled by a given ion algebraically by using the transparency of the grid. Say your grid is 99% transparent, that is to say that the wire occludes 1% of the solid angle of a spherical surface. The chance an ion passes through once (one diameter) is 0.99, the chance the ion passes through twice (two diameters) is 0.99*0.99 and so on.
If you run a thought experiment following a single ion, you can see that you either need the grid to be extremely transparent such that many millions of oscillations are allowed before the average ion impacts the grid; or you need an extraordinarily large grid such that an ion travels the required distance in only a few recirculations. Both ends of the spectrum are not very practical. Either the grid needs to be so fine that you cant physically build it (and/or it burns itself up), or the grid needs to be so big it would be a sizable fraction of the diameter or Earth.
If you don't want to take my word, look up the literature from University of Wisconsin, Japanese universities which currently have the most active IEC programs in terms of theory and experimental systems. It is well accepted by the field that IEC will never produce net gains though they are useful for other applications.
For your second point, speaking in broad strokes, fusion power would be captured either directly by energetic charged products traveling though an electric potential, or photoelectrically converting photons with an 'onion shell' geometry of plates, or thermally catching neutral products and running them through a steam cycle. Generally, those three options are listed in terms of the most efficient to the least efficient. Which approach is most reasonable depends on the type of fuel you are using and a large number of physics/engineering constraints.
tl;dr fusion is easy, energy efficient fusion is stupidly difficult.
Edited to fix dumb math error, thanks Tom.
Last edited by prestonbarrows on Sat May 30, 2015 1:34 pm, edited 3 times in total.
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Tom McCarthy
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Re: Daniel Villageliu
Welcome Dan,
Just a note on one of Preston's points: Are you sure it's a linear calculation, rather than exponential when calculating the chance of an ion passing through a grid? I'd have thought it would have been 0.99^x, as is done in terms of chance, rather than x(0.99), ...I could well be wrong, would you be able to confirm this Preston?
Best of luck with your work Dan,
Tom
Just a note on one of Preston's points: Are you sure it's a linear calculation, rather than exponential when calculating the chance of an ion passing through a grid? I'd have thought it would have been 0.99^x, as is done in terms of chance, rather than x(0.99), ...I could well be wrong, would you be able to confirm this Preston?
Best of luck with your work Dan,
Tom
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prestonbarrows
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Re: Daniel Villageliu
You are right Tom. That is why you shouldn't post after midnight...
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Tom McCarthy
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Re: Daniel Villageliu
Haha, keep at it - You put in the major work and I'll clean up after!
Tom
Tom