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Plasma Power Plants

Hotter is better -- and we need the practice!
  [vote for,

The Second Law of Thermodynamics tells us that the greater the temperature difference between two volumes of matter, the more useful energy we can extract, as we allow the heat in the hotter matter to flow toward the cooler matter. This is somewhat analogous to saying, "The taller the waterfall, the more hydro-energy we can extract." Today, our best engineering lets us extract about 50% of the heat energy produced in large power plants. This includes conventional nuclear fission reactors. To get greater efficiency, we need to run our power plants at higher temperatures -- but we are limited by the physical properties of the materials we use, which must contain those temperatures.

An extremely large leap in temperatures has been under development for the last fifty years or so. While ordinary power plants operate at temperatures of perhaps a couple thousand degrees, nuclear fusion reactors will operate at a hundred million degrees (Fahrenheit) . There is no such thing as ordinary matter at such a high temperature; atoms bounce around so violently that they smash themselves apart into ions and electrons, becoming the "state" of matter known as "plasma". However, since ions and electrons are electrically charged, they can be manipulated and contained by magnetic fields -- and it is possible to extract useful energy directly as electricity, at 95% efficiency or so.

The problem I wish to address in this Idea is that I think we are taking too big a step, in going from thousands to multi-millions of degrees. We need the practical engineering experience of working with plasmas on an industrial power-plant scale, and not on the mere research-reactor scale. Not to mention that we still haven't tamed fusion enough to be able to do any real power production with it. So, I suggest we consider building some power plants that operate at some intermediate temperature, say a few hundred thousand degrees. When fusion is ready, so will be the engineers!

Immediately some detractor will say that such a thing is impossible. Current power plants usually operate at a couple thousand degrees for another key reason, than mere properties of temperature-confinement materials. The chemical reactions between coal and oxygen, or oil and oxygen, or whatever and oxygen, produce heat by ALSO producing stable chemical compounds (carbon dioxide and water, mostly) that can continue to exist as chemical compounds, in spite of the temperature. Should the temperature be so hot that those compounds cannot form, then there is essentially no associated production-of-chemical-reactant energy!

However, not all existing power plants depend on mere chemistry for their operation. There is absolutely nothing to prevent nuclear fission power plants from operating at a hundred thousand degrees -- or even at a hundred million degrees. All we have to do is design the things in terms of magnetic-field plasma containment, and not ordinary material-bound heat confinement! Indeed, such a range of operating temperatures is perfect for gaining the engineering practice needed for large-scale adoption of fusion power -- when it arrives. Not to mention that fission power plants do not produce any greenhouse gases or other air pollution.

Now, of course I know that fission power plants have historically come with their own dangers, notably those of catastrophic failure and large amounts of radioactive waste. The first, however, is TOTALLY sovlable with appropriate attention to the Laws of Physics when designing a fission reactor (see PIUS link). When you get Mother Nature involved in your engineering, you can end up with very pleasant levels of reliability and safety. Some people even think that such reliable fission reactors may actually offer significant competition to the future adoption of fusion power. Next, with respect to radwaste, it just so happens that most radwaste is stuff that has been EXPOSED to fission reactors, and not stuff that was actually part of those reactors. It follows that appropriate engineering, which minimizes the amount of ordinary matter being exposed to nuclear fission reactions, will greatly reduce the production of radwaste. And, it just so happens that a Plasma Fission Reactor is exactly BOTH kinds of engineering design!

As you may know, a nuclear fission reactor depends on a "chain reaction" which works like this: Start with a "fuel nucleus", which can be either U-233 (made from Th-232), U-235, or Pu-239 (made from U-238). One fuel-nucleus naturally fissions (splits into two smaller nuclei) and also releases two or three individual neutrons. A tiny amount of natural fission is always occurring in nuclear fuel (cosmic rays can do that, if nothing else). The neutrons released are "fast"; so it can be easy for them to zoom entirely out of the reactor before they encounter more fuel-nuclei. "Moderator" nuclei are used to get in their way, to be involved in collisions that slow them, turning them into "thermal" neutrons (a reference to being about as temperature-energetic as the atoms in the reactor). Note that the collisions tend to bounce the slowed neutrons back toward the place they came (presumably the center of the reactor). A Thermal neutron has a much greater chance of encountering a fuel-nucleus than a fast neutron, and when it is absorbed, it CAUSES that fuel-nucleus to fission. This releases two or three more neutrons, and so the chain reaction can continue. A steady chain reaction depends on one neutron being absorbed for each ATOM that fissions. The reaction will die out if it is less than one-for-one, and catastrophe can result if it is more than one-for-one. But total numbers are important, too. A reactor that is just starting up needs to have a greater-than-one-for-one ratio, until the total numbers of neutrons being absorbed from fissions matches the power-production goal. (Meanwhile, it is known that we can use the "wasted" neutrons, to create U-233 from Th-232, and Pu-239 from U-238, thereby increasing the total amount of fission-fuel by quite a bit. Less than 1% of natural uranium is the naturally-fissile U-235, and thorium is four times as common as uranium...)

Now consider a torus (donut-shape), which has two or three diameters to talk about. There is the diameter of the hole, the diameter of the whole, and their difference, which is the diameter of the tube that is bent into being the body of a torus. Mathematicians prefer to talk about radii, such as in this definition: "A torus has a major circular path laying in the xy-plane centered around the z-axis. The surface of the torus is constructed by sweeping the center of a circle with a radius equal to the minor radius along the path defined by the major circle." Translating, the minor radius is half the diameter of the tube, and the major radius is not half the diameter of the whole, but instead is half the diameter of the hole plus half the diameter of the tube. I ask you to contemplate a torus that is quite large, having a minor radius of ten meters, and a major radius of a hundred meters....

We surround that bent tube with superconductive coils. Because of the sheer size of the major radius, this tube does not bend sharply, and so a reasonably even magnetic flux will fill it (uneveness means plasma leakage). All the air is pumped out of the torus, and we start injecting plasma at a minimal temperature (above 5000C, everything is plasma). The plasma must contain three main components, defined by nuclear and not ordinary physical properties: fuel, moderator, and coolant. It is OK that they will be thoroughly mixed; their electromagnetic properties will differ enough to allow sorting as needed. Note the interesting fact that ordinary helium has the nifty properties of being suitable as both moderator and coolant -- AND it is extraordinarily resistant to becoming radioactive. Finally, another interesting fact is that the neutron possesses a magnetic field, and so may be partially confine-able by the same field that confines the working plasma.

The large minor radius of this torus is necessary to accommodate the fact that plasmas are typically less dense than solids. Some of that density difference (maybe even all of it) can be overcome by suitably boosting the strength of the overall magnetic field, thereby squeezing the plasma. But the lower the density, the larger the container must be, to ensure that a thermal neutron has the same chance as in a solid, of encountering a fuel-nucleus. I'm specifying a large minor radius to ensure this idea is workable. Also, a key protective feature of this design is that a plasma behaves like a gas; when it gets hotter it expands (automatically reducing the rate of interaction with neutrons). We need space for that.

Neutrons that do escape the plasma will naturally tend to make the body of the reactor radioactive. This is essentially the same as what would happen in a fusion reactor, because it will produce neutrons, too. But the problem is worse in a fission reactor (greater numbers of neutrons per unit of produced energy) -- which is nevertheless also an opportunity. The opportunity is to experiment NOW with ways to solve the neutron problem, so that when fusion reactors are built, they will be no trouble at all. One interesting partial solution comes from the physical and electromagnetic differences between helium and fission-fuel. At any given temperature, the results of applying that magnetic field will be a natural tendency for the heavy nuclei to concentrate in the center of the toroid, while being surrounded by lighter nuclei. Remember, the lighter nuclei moderate the neutrons, bouncing them back toward the center.... Next, I recommend adding hydrogen as well as helium to this fission reactor. Hydrogen is an even better moderator than helium. If the neutrons are slowed enough, they may indeed be almost completely confined by the magnetic field in the torus. What happens to them then? Neutrons are unstable, and half of them naturally turn into harmless hydrogen after about 12 minutes. Just think! If we can affect the weak magnetic fields of neutrons to confine them at a hundred thousand degrees for 12 minutes, then how long can we affect the much stronger fields of fusion plasmas at a hundred million degrees? This is exactly what I meant, about needing and getting the engineering experience, to prepare for fusion power plants! Meanwhile, of course, we can also be solving NOW the immediate problem of needing more power plants, while reducing both the production of greenhouse gases and the rate at which the world's petroleum resources are being forever used up....

Vernon, Sep 09 2003

PIUS http://www.rcgg.ufrgs.br/fbnr_tec_ing.htm
A naturally safe fission-reactor design [Vernon, Oct 06 2004, last modified Oct 17 2004]

Future Competition http://www.itp.tu-g...f_interest_1new.pdf
What will fusion really be up against? [Vernon, Oct 06 2004, last modified Oct 17 2004]

magnetic confinement of neutrons http://museum.nist..../item.cfm?itemId=61
A technology to be improved upon, of course! [Vernon, Oct 06 2004, last modified Oct 17 2004]

Mass Spectrometry http://www.mhhe.com...ent/olc/ch13ms.html
How magnetic fields can be used to sort ions by mass [Vernon, Oct 06 2004, last modified Oct 17 2004]

Offtopic link for Detly http://www.nemitz.net/vernon/GHOSTLY.pdf
"The Aethereal Interpretaion of Quantum Mechanics" -- which despite its name, is just as "good" as the Copenhagen, or Many-Worlds, or Bohm's, or the Transactional, or any other recognized Interpretation. [Vernon, Oct 06 2004, last modified Oct 17 2004]

Subatomic particle info (including spin) http://na47sun05.ce...entalparticles.html
To support annotation describing spin-units of whole-number and half-integer amounts. Do note the "Unified Electroweak" particles have the same spin as gluons, which hints at why we can expect to Unify the Strong Force with the ElectroWeak Force. (Unifying Gravitation into the mix could be tough; I once read somewhere that the graviton may have a spin of 2.) [Vernon, Oct 06 2004, last modified Oct 17 2004]

Nuclear Fusion Basics http://www.jet.efda...ontent/fusion1.html
[philmckraken, Oct 06 2004, last modified Oct 17 2004]

Thermionic Conversion http://topics.aip.org/8460N_FS.html
Lots of details behind modern SNAP generators. [Vernon, Oct 17 2004]

Stuff Falling from the Sky http://answers.goog...hreadview?id=192044
[philmckraken, Oct 17 2004]


       No physicist, I will try to summarize: A fission reactor in which the fissile materials are in the plasma state rather than solid rods. The reasons: 1:plasma can get hotter and may provide more efficient conversion of heat to electricity. 2: this will be good practice for necessarily hot fusion reactors.
bungston, Sep 09 2003

       please shorten your ideas... I (and probably everyone else) can't be arsed reading this. I think it might be a rant, but I can't tell...
suctionpad, Sep 09 2003

       Could be a contest. Who can summarize one of Vernon's ideas in the shortest sentence possible and still hit the major points.
RayfordSteele, Sep 09 2003

       Croissant for [Bungston]'s summary.
FloridaManatee, Sep 09 2003

       I must confess I didn't read all of this. I'm going to wait for the movie to come out.
lostdog, Sep 09 2003

       [RS] - Maybe a "Vernon Haiku"?
Detly, Sep 09 2003

       suctionpad: I take it you are not familiar with Vernon's work? Anyway, save your breath.
DrCurry, Sep 09 2003

       The idea sounds good, not that I would know if it sounded bad.   

       Folks, I forgot to mention a couple of other things about the suggested reactor. While it features an automatic control against a runaway reaction (hotter plasma expands, as described), for a more ordinary control of the reaction rate (typically involving neutron-absorbing substances in "control rods"), all we have to do here is reduce the strength of the magnetic field. This reduces the compression effect on the plasma, and also lets it expand. No need to cause stuff to become radioactive, just to keep this reactor under control!   

       Next, the physics of ions in magnetic fields has produced such devices as the "mass spectrograph", which can separate nuclei from each other quite precisely. Fission products can be extracted as continuously as new fuel is added to this reactor. Also, pure radioisotopes for research purposes become more easily available in larger quantities, thanks to this design. And the most highly radioactive nuclei can be sorted out and placed in SNAP generators (System for Nuclear Auxiliary Power), which absorb radiation, convert it to heat, and then electronically convert the heat into electricity. Such "thermionic conversion" has been around since the 1960s, and is typically used in such space probes as the current Cassini-Huygens mission to Saturn, where power must be available for years, but sunlight is too weak for solar cells. Much of the radwaste from this reactor will get USED, not dumped as if worthless.
Vernon, Sep 09 2003

       Can't we just give up nuclear energy for good? Whenever you start messing with fission or fusion you are going to run into unforseen problems, which in this case could be far more catastrophic than any nuclear accidents we've had so far. The risk just isn't worth it.   

       And if we spent half the money we invest in nuclear and oil research instead develping large scale solar energy production methods, we could be getting all our energy for just about free forever.
oxen crossing, Sep 10 2003

       I wanted to ask Vernon how could the plasma magnetically contained idea be applied to other energy sources.   

       I am actually thinking on solar energy. Supposing we can optically concentrate as much as we want sun radiation on a single spot, we can attain as high as we want receiver temperatures, theorethically.   

       Some questions:   

       1) How could the plasma absorve solar radiation? It is not possible through container heating. Radiation should be directly absorved by plasma.   

       2) Which kind of machine could transform the intense heat into electrical energy?
rpardell, Sep 10 2003

       [DrCurry] this is the longest I've seen - are there even longer ones?
suctionpad, Sep 10 2003

       [Vernon]: I'd like to make a polite request for you to review your writing style. I feel that your ideas and purpose often get lost in verbiage. [bungston] has pretty much summed up the idea in about 50 words. Yours was closer to 1750.   

       You don't have to explain the fission process at all. Leave a link if you like, and those that are interested can learn about it - those that already know can then continue with the more novel aspects in your idea.   

       Ditto the descripion of a torus (except maybe reminding people that it is doughnut shaped).   

       It is a characteristic of your ideas that you will go into detail and labour some aspects, at other times gloss over points. I think you should find 1 consistent point and then make all other points succinct and satellite to that. I do not intend to criticise, I merely suggest that a more concise style will encourage people to read your ideas (which, to be quite frank, at the moment can almost be a chore).
Jinbish, Sep 10 2003

       ahhh...just looked up his ideas, and the first one was significantly longer than this one.
suctionpad, Sep 10 2003

       [suctionpad]: yes - I was just about to dig it out for you. "12864", could be a good idea. But I'll be damned before I waste my time and effort to find the actual merit in the idea. I'm sure it's there somewhere hidden within the 11,913 words.
Jinbish, Sep 10 2003

       rpardell, your solar energy idea seems quite good. A donut with appropriate windows, even if surrounded by coils, should offer ways to let the light in. Also, plasmas are pretty good at interacting with light -- plasmas are 100% made of electrically charged particles, and there is a pretty strong interaction rate between charged particles and photons. (It takes quite a few years for photons generated in the Solar core to travel some 400,000 miles to reach the surface of the sun, due to interactions with plasma ions. After escaping from the surface, photons only take 8 minutes to travel 93,000,000 miles to reach Earth.)   

       I am not certain of the exact technique that can be used to convert plasma energy to electricity at the claimed 95% efficiency; it was something I read in a science magazine a number of years ago, a claim made by some fusion researchers. Last night I spent some time looking for it on the Web (I wanted to add another link), but couldn't find it. I do think, however, that the notion is somewhat based on electrical induction.   

       Jinbish, those who say I write too much and those who say they don't understand what I write are about equal in quantity. I am usually in the position of having an idea that depends on several factors working together. Each factor may be a somewhat advanced concept, over ordinary high-school science, which I assume most people know. I try to write so that they, possibly aided by a good dictionary, can grasp the advanced concepts, and then see how those concepts fit together in the overall idea. And, just because I independently studied "nuclear chemistry" back in high school, that does not mean I can expect most readers here to have also done that. Spending one paragraph on it is not wasteful -- and can be skipped by the knowledgable -- although perhaps I would have done the link thing if only I had thought of it. I didn't think of it simply because I didn't need to look up any reference material to write that paragraph. --And, how much longer would somebody have taken to read the more thorough equivalent material at a link? Next, with respect to the donut, I wanted to describe it simply, but I also wanted to specify 10x100 meters, which makes no sense without talking about (and defining!) "minor radius" and "major radius"). One thing sometimes unavoidably leads to another. Finally, while the rationale for an idea (bungston's summary) may make it worthy of posting, the full consequences of it should also be posted, to the best of one's ability. Bungston didn't happen to mention safer fission reactors with less radwaste, did he? But how could I claim such things without taking the space to describe them?
Vernon, Sep 10 2003

       [Vernon]: Its not the volume - go nuts with the volume! I just happen to think that your arguments/ideas would benefit from a more precise (maybe technical) style of writing.   

       (For example, "12864" is sometimes written in a conversational style, that I feel works against its detailed and technical nature.)
Jinbish, Sep 10 2003

       [Vernon] Perhaps an abstract (or "Executive Summary") at the start of such a long and detailed technical discussion is called for here. Its unfair to leave it to [bungston], or someone else, particularly when you are the person with the real knowledge of the idea.   

       Most people will view the length of the post, see the topic, and decide they are unable to understand without even giving it a go. You could give the less gifted a more accessible initial description, and if they are interested in the subject matter they will be drawn into the full glory of the remainder of the post.   

       Oh...and I've yet to meet someone who doesn't know what a donut looks like.
suctionpad, Sep 10 2003

       A side note for Vernon,   

       They are currently working on a toroidal plasma generator with magnetic field containment, it creates electrical energy much similar to how conventional generators work ( fixed magnets and rotating magnetic fields). However, right now it takes more energy to maintain the magnetic field that the generator produces.   

       I think it is called the ToroMat reactor,
SystemAdmin, Sep 10 2003

       Vernon is my hero.
DeathNinja, Sep 10 2003

       In a plasma, electrons are separated from protons, am I correct? How about the particles in the nucleus? Do they stay together? I guess so, otherwise this just couldn't work.   

       Another thing which some one might help me with: If a fusion reactor goes wrong, what happens? I guess that if the magnetic field dies then the reaction chamber will probably melt a bit, and maybe the spare hydrogen might catch fire or explode, but would there be any wider reaching problems? How about with this? Would the reaction just stop or would you have an uncontrolled reaction?
RobertKidney, Sep 10 2003

       Vernon, while your ideas often have merit, the writing style is difficult to read. The level of detail and paragraph order seems more suited to patent application then initial presentation. May I suggest that you include a brief synopsis (maybe 1 or 2 paragraphs of 100 words or less) in the beginning, followed by as much detail as you care to include in the rest of the idea? It would give us an idea of what you're trying to propose, and let those of us inclined to learn more continue to read.   

       Anyway, +
Freefall, Sep 10 2003


       (newspaper style summary-->text format seconded, though I quite enjoyed this idea)
Worldgineer, Sep 10 2003

       The idea of dampening the reaction by slacking up on the magnetic field is slick. Croissant.
bungston, Sep 10 2003

       Folks, we shall see, in an upcoming idea, whether or not I can do a synopsis that doesn't turn into the explanation itself, heh heh.   

       oxen crossing, please remember that the biosphere runs on solar power. The more sunlight we intercept and convert to electricity, the less light there is for the plants at the base of the biosphere. Sure, there are deserts we can cover with solar panels without harm, and even get enough power for most of our needs. However, as population rises, needs will grow, while sunlight hitting the Earth remains basically constant. The difference in needed power has to come from somewhere else, and oil/coal/gas will run out long long before uranium/thorium/hydrogen.   

       Mr Burns, yes, I know there are other Vernons out there in the world.... :)   

       SystemAdmin, I'm pretty sure what you are talking about is the Tokamak fusion reactor idea, which has been under development for a number of years. I make no bones about the similiarity of this idea to existing magnetic-confinement fusion research. But fusion has a ways to go yet before it is workable on a large scale, while we know that fission works just fine at lower temperatures than fusion. We need more power plants NOW, that don't add to the Greenhouse Effect. Not many economically viable options out there....   

       RobertKidney, yes, a plasma consists of atoms that have lost at least one electron each, and those lost electrons are also part of the plasma. Atomic nuclei are usually unaffected by temperatures less than a billion degrees (hydrogen being the main exception). Also, a fusion reactor will not contain a large amount (mass) of reactant material. Should the magnetic field fail, the plasma expands and cools, in accordance with physical laws describing gases. A cooled plasma cannot sustain fusion, so the reaction will immediately cease. The worst that is likely to happen to the inside surface of the reaction chamber is some microscopic pitting (it will be damaged more by neutron bombardment while the reaction is going on).   

       dag, magnetic confinement techniques will probably forever be too bulky to mount on a Humvee. Inertial confinment techniques, or perhaps the ballyhooed Cold Fusion thing, are much more likely to fit. NO sort of fission reactor will fit, because of the needed mass of radiation shielding.
Vernon, Sep 11 2003

       Vernon, go build this thing. It sounds like you're on the way to being able to do so. (+) And don't worry about losing readers with the long ideas. (A summary is a good idea though.)
Madcat, Oct 22 2003

       Thanks, Madcat. All I need is oodles of $$, and a supply of fission fuel....
Vernon, Oct 23 2003

       The preceding annotation has been intercepted by Carnivore, and Vernon will be tackled momentarily by a robotic dog authorized by the Patriot Act...
TerranFury, Feb 11 2004

       I was hoping for fission energy through agriculture.....
normzone, Feb 11 2004

       Its interesting that you mention Inertial Electrostatic Confinment in a comment as a possible route to fussion, but havent considered an IEC fission reactor.   

       An IEC fission reactor would of course have the advantage that the fission products would exit from the core with a relativly narrow spread of momentums which would allow the use of a decelerating electric field to extract energy directly.   

       Unfortunately I don't think any scheme of neutron moderation is ever going to make a plasma fission system work. Even if the neutrons are slow, the fissable material is still moving fast (by definition of being a plasma). I can't remember if the purpose of the moderator is to slow the neutrons so they spend more time in the core, or to slow the neutrons to increase the chance of an inelastic scattering event.   

       OTOH if you can get the plasma dense and hot enough you might be able to overcome the electrostatic forces between nuclei, and achieve fission that way. If this worked you might be able to select an aneutronic reaction (one that doesn't produce neutrons)
smeghead, Apr 01 2004

       [smeghead], if by Inertial Electrostatic Confinement you are referring to the Farnsworth Fusor, then yes, I do not consider it a reasonable way to handle fission reactions. The Fusor has the purpose of accelerating nuclei so that they can collide and fuse, but a fission reactor does not involve colliding nuclei, and does not need accelerated neutrons --which won't accelerate, anyway, inside an electrostatic field, since neutrons have zero electric overall charge. Also, a fission reactor needs something known as "critical mass" of fuel in order to work -- and when that mass is converted to very volumous plasma, we are going to need a quite LARGE volume. That would be an extremely large Fusor (although such may be needed, anyway, for practical fusion power). So, because such a large volume of plasma may be difficult to contain using only electrostatic fields, and because a fair percentage of fission neutrons MUST be contained for a chain reaction to persist, I specified the magnetic toroidal shape.   

       The purpose of moderating the neutrons has to do with the "absorption cross section" of a fissile nucleus. It is convenient to picture such a nucleus as a tiny point in the exact center of the bulls-eye of a shooter's target-circle -- but the WHOLE bulls-eye is a zone that if a neutron enters, then the nucleus will absorb it. HOWEVER, the size of that zone happens to be smaller for faster than for slower neutrons! (There is a "duration in the zone" aspect of absorption.) So, moderating/slowing the neutrons makes it easier for them to hit the bulls-eye... On a more humorous note, you might find it entertaining to know that the unit of measurement of absorption-cross-section is called the "barn", and yes, this term DOES derive from the phrase, "He couldn't hit the broad side of a barn!"   

       Finally, regarding aneutronic fissions, these are known to require more energy to cause-to-happen, than you get from the resulting reaction. Because fissionable nuclei start with a LOT of protons, and to make other protons collide with them means overcoming a rather extreme electrostatic repulsion.
Vernon, Apr 01 2004

       Hmm, yes, I use IEC and the Farnsworth Fusor to mean the same thing, but we seem to be thinking of the device as operating in different ways. You seem to be suggesting that the Fusor is used to accelerate particles towards each other, where I think of the device as creating a steep potential well to trap the particles at the center of the device. This is largely irrelevant anyway since I was only suggesting that the fusor provides a ways of confining the charged nuclei, which the tokomak also does. As for which is better at confining charged nuclei, a tokomak or a fusor, I couldn't say, except that tokomaks seem to provide better confinment at greater cost.   

       I'm also a little confused as to how you wanted to confine the neutrons in the tokomak. You seem to be suggesting that the neutrons magnetic dipole will allow you to do this. Won't the dipole of the neutron just align with the field lines of the tokamak without affecting the velocity of the neutron at all? Personally I can't think of anyway of confineing the neutrons short of surrounding the reactor with a neutron reflector (I think U-238 is usually used for this). Hence my advocacy of fission involving nuclei collisions despite the high temperatures necessary (actually the other part of my argument here was that even if you can confine the neutrons, you can't moderate them relative to the nuclei because the nuclei are moving randomly at a speed proportional to the plasma temperature)
smeghead, Apr 05 2004

       [smeghead], in a way, the Fusor is both an accelerator and a potential well. Recall that fuel is added to a Fusor from an external source; the construction of the Fusor is such that ions just entering its outer sphere are accelerated by electrostatic fields toward the center. Obviously once such an accelerated ion PASSES the center of the sphere, those same fields will decellerate the ion, and then (ion unable to escape this potential well) re-accelerate it toward the center. This acceleration is what the ions NEED to have, to be moving fast enough to fuse when interacting at the center of the sphere.   

       Next, I specifically mentioned that a fission plasma must contain moderator-nuclei as well as fuel nuclei. I also made an assumption (not so precisely stated as here) that if the toroidial magnetic field was strong enough, and if the neutrons were slowed enough by moderator nuclei so as to be trapped by that magnetic field, then EVENTUALLY those trapped neutrons would encounter fuel nuclei, thereby perpetuating the chain reaction. However, your remark about neutrons merely following lines of magnetic force does have merit, since I expect the fuel nuclei to be mostly concentrated in the center of the minor radius of the plasma torus, while less massive stuff (moderator and therefore also neutrons) will surround it.   

       Nevertheless, to minimize the overall size of a plasma fission reactor (recall requirement of a critical mass, a minimum quantity of fuel converted to thousands-of-times-more-volumous plasma), we will want as dense a plasma as we can get. (The needed magnetic fields will naturally also be suitable for fusion reactors, of course.) It seems to me unlikely that the neutrons will be able to stay trapped on any one magnetic line, due to all those nuclei in a dense plasma, and consequent collisions (mostly with moderator nuclei, I expect). Sure, we can expect some of those bumped neutrons to head toward the walls of the reactor vessel, and there will likely not be any easy way to bounce them all back. I have my doubts regarding using U-238 for that; but see nothing wrong with using those inevitable escapee neutrons to breed more fission-fuel from such a supposed reflector....
Vernon, Apr 05 2004

       Actually the neutrons won't follow the lines of magnetic flux at all. Charged particles follow lines of magnetic flux because their magnetic field is related to their velocity (IIRC the magnetic vector potential is aligned with the velocity vector, but its been a while since I did magnetism so don't quote me :-) The neutrons magnetic moment however is intrinsic due to angular momentum of the quarks, and oriented independent of the velocity.   

       I had a think about how you might confine a magnetic dipole with a magnetic field and indeed there is a way, but you need to setup a gradient, so that the field is strongest at the center of the torus. Considereing the weakness of a neutrons magnetic dipole, this had better be a BIG gradient :-)   

       You might be interested, I recently found (due to the interest this proposal provoked) another idea combining fussion and fission technology. The idea was to use the fussion (in this case provided by a fusor) to provide neutrons to drive a sub critical mass of fissile material. The fussion reaction its self wouldn't produce net power output, but the fission reaction would. Unfortunately I can't find the link any more :-( I did seem like a fairly serious proposal though, mentioned on a US DoE website (or was it DoD? something with a .gov at the end anyway :-)
smeghead, Apr 06 2004

       [smeghead], some years ago I first read about magnetic confinement of neutrons (they were seeking to accurately determine the decay rate), and I seem to recall them using a six-lobed field shape (cross section of field, that is). Now, in a plasma-confinement environment, such a field may or may not be worthy of consideration -- though it seems to me that something that confines UNCHARGED particles might be extremely good at confining charged particles. (Yet those six spokes also looked to me like plasma escape routes, and so I shan't push the issue.) Anyway, one feature of toroidial plasma is that (as done in Tokamak systems) a current flow can be induced in the ring, which yields a pinch effect. This also qualifies as (quoting you) "the field is strongest at the center of the torus". Unfortunately, that induced current can only be caused temporarily, so more work needs to be done -- but then, that is why this Idea is here at the HalfBakery. (Now I'm contemplating multiple pulsating-DC induction sources, such that when some are fading others are strengthening....)
Vernon, Apr 06 2004

       [Vern] - you know that neutrons have magnetic moments?
Detly, Apr 06 2004

       Is that like an attractive senior moment?
bristolz, Apr 06 2004

       [Detly], I'm not sure if you are punning. The neutron, although it has no overall electric charge, does possess an overall mangetic field. This is associated with the elctric charges of the quarks inside the neutron -- those charges cancel out, but their magnetic fields don't. (It could be said that a large reason for supposing that neutrons HAD to be made of smaller charged particles was its otherwise-unexplainable magnetic field.)
Vernon, Apr 07 2004

       No, I wasn't sure if you knew - just from your discussion of magnetic confinement. It's one of those oddities I love (along with the fact that only about 30% of the hadrons spin is accounted for by quarks).   

       I'm still trying to see a pun in that, though.
Detly, Apr 07 2004

       [detly], what of the virtual-gluons that hold the quarks together inside those hadrons? I don't recall what their spin properties are, but might their (temporary yet constantly-replaced) presence be able to explain that other 70% of hadron spin?
[Regarding pun, somewhat weak: think "a moment during which one exhibits a magnetic personality".]
Vernon, Apr 07 2004

       I would think from angular momentum conservation that any virtual pairs created should cancel. If I'm thinking correctly, virtual pairs don't violate conservation laws because of the uncertainty principle (a virtual pair can only exist for t = h/(2piE), for example).
Detly, Apr 07 2004

       [Detly], yes, that is basically true. On the other hand, consider the formation of a hadtron/anti-hadron pair, which could INCLUDE the formation of a separated pair of virtual gluons. Thus in each of the two hadrons you could have some extra spin that is tied to the virtual gluons -- some spin that persists as spontaneously-appearing virtual gluons replace those-which-are-about-to disappear. (For MUCH more on the rationale behind that sentence, see this essay: http://www.nemitz.net/vernon/GHOSTLY.pdf)   

       And, while I know that the "color" aspect of gluons mean they have both colors and anti-colors, they ALSO can come in combinations of three --which right there could be a reason for unbalanced spin. That is, AS a hadron/anti-hadron pair form, suppose we also get two triplets of gluons with balanced color and spin, but those triplets separate (one per hadron), retaining balanced color but leaving excess spin in each hadron....
Vernon, Apr 08 2004

       My understanding of particle spin on subatomic particles, [Vernon], is that even when three particles are generated the collective spin is equal to zero. As [Detly] pointed out, conservation of angular momentum preserves the status quo. No violation of the laws of thermodynamics, even for hadrons and bosuns and gluons and quarks.   

       I am also concerned at the possibility your idea raises. A catastrophic failure of the magnetic bottle would see the entire plasma volume contained flash to atmospheric fallout. With a heavy metal reactor you can at least clean it up. This idea is a "hot" gas cloud from the moment of breach. Fish for you.
Zanzibar, Apr 08 2004

       [Zanzibar], since the property called "spin" for bosonic particles (like gluons) is specified in whole units, I'd sure like to know how three of them (plus or minus, any combination) can be combined to equal zero. Meanwhile fermions like quarks have spin specified in half-units, so if the overall neutron (or other hadron) has a combined spin of one-half (result of quarks' +1/2 +1/2 -1/2), then --IF-- there is ALSO some gluonic spin involved, the combinations become much more varied and interesting. Some of them would have the total spin from the quarks be 1/3 of the total spin of the hadron, with the other 2/3 coming from the total spin from the gluons....   

       Next, regarding your description of catastrophic failure, you seem to be missing the fact that a plasma normally exists inside a vacuum, and that a vacuum has to be contained by rather impermeable walls -- and the larger volume of vacuum enclosed, the thicker and stronger those walls have to be, to keep from collapsing under exterior atmospheric pressure. Please recall that I have specified a VERY large evacuated torus here.... Furthermore, you have missed the critical fact that if the magnetic field fails, then the plasma expands (and cools!) and its ability to sustain a chain reaction dissipates (due to increased space between fissile nuclei, making neutrons more likely to miss). Next, if the vacuum shell is breached, atmosphere will rush IN, and the plasma will be completely quenched into whole atoms (no ions will survive) by the vastly cooler ordinary air -- and, finally, oxygen in the air will combine with any uranium or plutonium atoms, making refractory oxides, which are not hardly gaseous substances. With respect to fission products, do recall that the ordinary operation of this reactor allows them to be filtered out of the plasma constantly (most likely for practical usage in SNAP generators). Only comparatively trace quantities will be present at any moment. Your fears are thus quadruply unfounded.
Vernon, Apr 08 2004

       Fusion Power Sounds promising but it is NOT!! If you use up all the hydrogen on earth.... Then we will all die!!!! of thirst!!!! Remember the deuterium is extracted from water!!!!! The water on Earth is in an finite amount even though it's alooootttttt of water. So it may take a million years to use that up on Fusion. I suggest find a way to recycle the hydrogen and oxygen in the PEM fuel cell   

       Think about it, last time we human think there is a lot fossil fuels and now do what happened? Its runnin' out
TTYO, Jul 09 2004

       [TTYO] - It's the same no matter what. The second law of thermodynamics says so.
Detly, Jul 09 2004

       [TTYO] Are you serious?   

       There is approx 10^15 tons of deuterium in the Earth's oceans. 10 grams of deuterium (when fused with 15 grams of tritium) would provide enough electrical energy for your entire life! So that's enough for 10^22 people's lifetimes...   

       Furthermore, this excludes the approx 40,000 tons of comet/meteorite material that falls on the Earth annually; some of which consists of ice.   

       (A bigger problem would seem to be sourcing lithium)   

       see links
philmckraken, Jul 10 2004


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