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Power Science

New 'Stellarator' Design for Fusion Reactors 171

Posted by Zonk
from the less-whoosh-boom-for-your-money dept.
eldavojohn writes "The holy grail of fusion reactors has always seemed 'just a few years off' for many decades. But a recent design enhancement termed a 'Stellarator' may change all that. The point at which a fusion reactor crashes is when particles begin escaping due to disruptions in the plasma. A NYU team has discovered that coiling specific wires to form a magnetic field may contain the plasma. This may be a a viable way to create a plasma body with axial symmetry, and a far better chance of remaining stable. Like other forms of containment this does require energy itself, but could bring us closer to a stable fusion reactor. It may not be cold fusion or 'table top' fusion but it certainly is a step forward. The paper is up for peer review in the Proceedings of the National Academy of Sciences."
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New 'Stellarator' Design for Fusion Reactors

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  • by Anonymous Coward
    ...they want credit.
  • by jd (1658) <<moc.oohay> <ta> <kapimi>> on Friday August 10, 2007 @05:45PM (#20190079) Homepage Journal
    ...Axl symmetry, they could produce something that was violently unstable but produced vast amounts of marketable energy and money.
    • If they used Axel symmetry, it would fight crime, too.
  • by Anonymous Coward on Friday August 10, 2007 @05:53PM (#20190141)
    The summary makes it sound like stellarators are something novel, which they are not. Research has been going on for decades, most notably with the German Wendelstein experimental reactors.
    • by iamlucky13 (795185) on Friday August 10, 2007 @07:01PM (#20190853)
      In fact, the stellarator design is almost as old as the Tokamak design. The first one was built in 1951.

      Somebody over at physorg got a little too excited about a fairly low-impact paper from NYU. If you read the abstract, you'll see that the paper just deals with the design of the coils for a stellarator.

      Most likely, this is for the National Compact Stellarator Experiment (NCSX) being built at nearby Princeton, which will be the first stellarator designed with a computer optimized plasma geometry. I think it will also be the largest stellarator to date, with 12 MW of heating capacity. In contrast, the JET Tokamak has 37 MW and the ITER Tokamak will have 110 MW of heating. Unlike ITER, NCSX will not be capable of break-even operation.

      Stellarators often get mentioned in fusion power discussions because they provide a more stable containment design, whereas a Tokamak needs one extra set of electromagnets to deal with the fact that the magnetic field is weaker at the outside of a torus of magnets than at the inside. Although a stellarator is therefore a little simpler in that regard, the geometry and plasma modelling is much more complex, and this in turn creates problems for designing the coils and the exhaust diverter. Because of this, most of the funding and research effort has gone to the Tokamaks.

      A little more info here: http://en.wikipedia.org/wiki/Stellarator [wikipedia.org]

      Anybody care to bet on whether this shows up on CNN's tech page in a day or two as some major "recent design enhancement?"
      • by Shag (3737)
        Princeton? I'm sure you know (as do I - I grew up not far from there and a friend of the family worked at PPPL) that they already did quite a lot of experimentation with the Tokomak [pppl.gov] design, and held the world record for fusion back in the 90s. In fact, the Stellerator is sort of an optimized Tokomak; the overall shape of the plasma is still a torus (Mmmm, donuts!) but it's "twisted" so it's not the same cross-section in all spots.

        I haven't read enough to really grasp why that's better, but 12MW is going t
  • by polar red (215081) on Friday August 10, 2007 @05:53PM (#20190145)

    Like other forms of containment this does require energy itself
    I find it weird that the amount of energy needed to contain, is less than the energy contained in the plasma. Can anyone explain this ?
    • Re:input-output (Score:4, Insightful)

      by Paul Pierce (739303) on Friday August 10, 2007 @06:01PM (#20190251) Homepage

      Like other forms of containment this does require energy itself
      I find it weird that the amount of energy needed to contain, is less than the energy contained in the plasma. Can anyone explain this ?

      Picture Chinese handcuffs
    • Re: (Score:2, Interesting)

      by thanatos_x (1086171)
      It's intrinsically harder to do useful work that raw work, just like it's easier to destroy than create....

      It could also be that it's a brute force attempt to force cohesion, and since force must be met with equal force it's very difficult. That also assumes it could concentrate the exact amount of energy at exactly the right point. Just imagine trying to not only stop a terrorist attack, but subdue them without lethal force. They need one leak to win. You need a perfect record.
    • Re:input-output (Score:5, Informative)

      by iamlucky13 (795185) on Friday August 10, 2007 @07:21PM (#20191035)
      Well, I'm not a plasma physicist, so I'm not intimately familiar with all the details, but one thing that jumps out at me right away is the distinction between energy and power.

      Energy is the ability to do work. Power is the rate at which work is done or energy is extracted.

      The plasma contains a great amount of thermal energy with a tendency to do work (by difussing to the reactor walls), so you have to set up a barrier to accomplishing that work. This is analogous to a dam holding back water. The water, due to it's elevation, has a lot of potential energy, but no power is required to hold it back. Power is extracted as it's let through the turbines.

      It's a little more complicated for a plasma. A charged particle moving through a varying magnetic field (like that surrounding the reactor) does work and thereby loses energy. As a result, there is a tendency, although less definite than with a dam and water, for the hydrogen ions to only move around in the reactor along lines of constant magnetic field strength.

      Once a magnetic field is established, it ideally takes no energy to maintain, except as charged particles move through it. So power only has to be supplied to the electromagnets to account for their inefficiency (0 under ideal conditions in a superconducting Tokamak) or as work is done on the field by charged particles escaping. Since most of the energy from the reactions is carried away by neutrons, which have no electric charge and therefore don't affect the field, the containment power is sufficiently smaller than the reaction power that this is theoretically feasible as a power plant.

      Actually, the biggest power demand in a Tokamak as I understand is for heating the plasma to a temperature where fusion will take place. The hotter it gets, the faster fusion occurs, eventually reaching a breakeven point energy is released by fusion faster than it is carried away by escaping neutrons and gamma rays. Then the plasma can sustain itself. We haven't gotten there yet.

      Sorry, the dam analogy isn't great and talking about charged particles in a magnetic field is a little abstract. Hope this helps.
      • by mako1138 (837520)

        Actually, the biggest power demand in a Tokamak as I understand is for heating the plasma to a temperature where fusion will take place. The hotter it gets, the faster fusion occurs, eventually reaching a breakeven point energy is released by fusion faster than it is carried away by escaping neutrons and gamma rays. Then the plasma can sustain itself. We haven't gotten there yet.

        Some subtleties:

        Fusion reaction rates are proportional to temperature, but only up to a certain point. The trend is roughly parabolic.

        'Breakeven' is usually calculated on the assumption that energy leaving the plasma is reinjected with a certain efficiency, typically 1/3. 'Ignition' is when the fusion reaction can go on without any external power input.

        Also, I realize it's a rough analogy, but the dam picture is inadequate. My professor described fusion confinement as "trying to hold jell-o with string".

    • Re:input-output (Score:5, Informative)

      by counterfriction (934292) on Friday August 10, 2007 @07:26PM (#20191067) Homepage
      "Energy" in the context of containing a plasma is actually work. They have the same units, so they're like exchangeable currencies (i.e. some energy will buy you work, and some negative work will buy you energy)
      The energy that a plasma intrinsically has (like kinetic energy) is just that; energy.

      Here's a related (but certainly not airtight) analogy: A brick can have some gravitational potential energy relative to the earth's surface. If you're standing on the ground, that brick will have some nominal gravitational potential energy. If you lift that brick 1 meter, you'll do some amount of work. If you're hanging over the edge of a helicopter at a couple hundred meters, that brick has substantially higher gravitational potential energy. However, if you lift the brick a distance of 1 meter, you'll still do the same amount of work.

      So, what's going on here is that a plasma can indeed have a lot of energy (relative to the earth's environment). However, the "energy" we're putting in is actually work to contain that plasma.
    • by kravlor (597242)

      There are two aspects to answer your question properly:

      • In a fusion reaction, you are invoking a nuclear process. Think E=mc^2; the E is resulting from the change in mass following the fusion of hydrogen (or strictly, its isotopes deuterium and tritium) to helium and a neutron. It can also be thought as a change in effective binding energy per nucleon (proton/neutron) in the nucleus of the resulting atom. So, even though you've got lots of mechanical (thermal) energy in the plasma which is actually causin
  • Huh... (Score:3, Funny)

    by Greyfox (87712) on Friday August 10, 2007 @05:55PM (#20190163) Homepage Journal
    SCO Loses and they figure out fusion* on the same day. Coincidence? I think NOT!

    * Sure it doesn't say they figured it out in TFA but humanity will point to this day and say 'That is the day SCO lost and they figured out fusion.'

  • Thorium reactors (Score:5, Interesting)

    by Bombula (670389) on Friday August 10, 2007 @06:00PM (#20190237)
    I was reading about thorium reactors recently. Seems like that's much closer to being rolled out, and its developers are claiming it solves a lot of the problems with existing reactors: it's more stable because thorium reactions don't chain the same way, it doesn't produce waste or plutonium, it can actually burn up other waste - including plutonium, and it can be used in some types of existing reactors (there are trials in Russian reactors right now).

    Does anyone know any more about this?

    • Thorium good, but if possible, fusion even better.

      If you want to see thorium-fuelled fission reactors in operation, you'll probably want to go to India. They're sitting on about a quarter of the world's thorium supply, and quite reasonably think that they ought to get some use out of the stuff.

      • Re:Thorium reactors (Score:4, Interesting)

        by Bombula (670389) on Friday August 10, 2007 @08:03PM (#20191269)
        Thorium good, but if possible, fusion even better.

        It's important to define 'better' here. Cost would seem to be an important consideration, for example. I don't know what the price tag of fusion is so far, but it's awfully, awfully high already and without a great deal to show for it. If we've already got a pretty good thing in thorium, and we already have the reactors, and there's enough thorium and uranium to keep us in electricity at present consumption rates for thousands of years, and it's non-polluting and all the rest, then how is fusion - a hugely expensive, so far unproductive technology - 'even better'. I'm not quibbling or trying to be antagonistic here - it's a serious question, and it needs a serious answer considering what's at stake: we need clean, non-polluting power that doesn't ultimately come from politically volatile parts of the world.

        • Re:Thorium reactors (Score:4, Informative)

          by mdsolar (1045926) on Friday August 10, 2007 @11:15PM (#20192513) Homepage Journal
          Solar and wind power fit the bill of being clean and local. A lot of our nuclear fuel these days comes from Russian weapons stockpiles. But the process of diluting it back down from weapons grade to fuel grade is not going all that well. In an accident in Tennessee last year that was covered up until congress stepped in, the plant managers thought that a big spill of highly enriched uranium soulution, enough to cause the kind of accident that killed 2 people in Japan 1999, was natural uranium. There were two places where the spill might have accumulated and cause criticality. That is pretty poor materials control if you don't know what it is that you are working with.

          Uranium reserves are estimated to be about 85 years at present use. Plans to extend the life of nuclear power all pretty much include breeder reactors (such as thorium reactors) and have unresolved fuel cycle problems. Fast breeder reactors are also illegal in the US owing to proliferation concerns. Their prototypes have also tended to melt down.

          The new reactor being planned for Calvert Cliffs has an estimated price tag of $2.50/Watt for construction alone, though with federal loan guarranties included in the Senate Energy Bill, this price will likely rise substantially. The price compares poorly with wind and solar, both at about $1.30/watt to build, but with much less in the way of operating costs, and obviously no fuel or long term waste disposal costs.

          The level of effort put into fusion has not really been that large. You hear about it, but compared to the Manhatten Project, out of which nuclear power came, it gets much less in the way of GDP. Renewables get even less than that. This was deliberate. The idea was to give it enough effort so that it would be ready when oil and coal ran out. The problem is that at the time, the growth in the use of coal and oil was not foreseen. So, fusion is actually right about on schedule. When it is here, there may be some trouble siting it since nuclear power plants squat on some of the better cooling resources and our storage in place policy for nuclear waste may keep these prime resources tied up for hundreds of years. But, wind was 20% of new generation in 2006 and is growing at 50% per year, while solar is growing at 30% per year and this should accelerate as the silicon purification bottleneck clears. So, fusion may enter a market that is already dominated by clean inexpensive power and thus find only niche applications in any case.
          --
          Go solar the easy way: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]
          • Here we go again. The vast conspiracy against solar and wind by those evil baddies. Please.

            Why not solar? The Solar Constant, that's why. 1.367kW/m^2. Typical yield is closer to 1kW/m^2. Then some genius suggests that we cover an area roughly the size of Arizona with solar cells to generate all of the power. Riiiiiiiiight. "Just cover all of the roofs, and we'll be set!" Riiiiiiiiiight.

            http://apod.nasa.gov/apod/ap970830.html [nasa.gov]

            Those are the roofs. Added up, they might add up to Arizona. Not likely though. Now
            • by Ed Avis (5917)
              Why not? There is a lot of empty space in Arizona.
            • by mdsolar (1045926)
              That is kind of a neat way of estimating the roofs. You can find a caluculation that takes a different approach here: http://mdsolar.blogspot.com/2007/08/roof-pitch.ht m l [blogspot.com]. You'll see that you are incorrect is saying that the area needed is the size of Arizona. An area that is 80 by 80 miles will do it.

              You are also incorrect on the durability of solar panels. They last 25 years at better than 80% rated capacity and will likely last 100 years at better than 40%.

              On wind, current capacity is 74 thousand
              • by ttfkam (37064)
                Go back and read my post again. Please.

                I was not commenting on their percentage output based on longevity. No solar panel has ever been 80% efficient as a percentage of the Solar Constant [wikipedia.org] . No panel will EVER get 100% of the Solar Constant. No energy transfer mechanism in the real world will ever be 100% efficient.

                Nevada has regions that get 9 kWh per square meter of sunlight per day on average over a year, or 375 Watts per square meter of average power. At 20% efficiency you get 75 of those. So we just divide the 1.2 TW of energy we use that we calculated earlier by 75 W per square meter to get the number of square meters we need. Divided again by a million gives 16000 square kilometers. The square root of this, 126 km, gives the length of the edge of the square which is about 80 miles.

                Okay, let's take a closer look together. You see that 20% reference? That does NOT mean the solar cells working at 20% of their capacity; that means that the solar panels are working at 20% of wh

                • by mdsolar (1045926)
                  20% effciency means 20% of what the Sun provides. If you look a little deeper, the solar number is for a concentrator and such thermal plants are being built with thermal storage. No batteries, just dispatchable solar power with a good match to changes in seasonal demand. And, that 80 by 80 miles covers the whole energy use of the entire country, not just Nevada and not just electric generation. It is just an example. Other places will use panels, that is kind of the point of looking at what roof space
                  • by ttfkam (37064)
                    First, your links:

                    Nuclear power plants are not either 100% on or completely off. The reaction can be moderated to many shades of gray, just as the comments on your own blog mention. You are presenting a straw man: not accurately representing how the opposition works and then taking them to task using your own sketchy characterization.

                    Your second link deals with the benefits of decentralization. Once again, I have no argument with that. I am not against wind and solar use.

                    If you look a little deeper, the so

            • by spectecjr (31235)
              You really don't want to do it this way anyway:
              Those are the roofs. Added up, they might add up to Arizona. Not likely though. Now imagine that you wanted to cover up Arizona with big pieces of paper, the whole state. I want you to imagine the scale of a project like that with just paper. Now I want you to reflect on the difficulty inherent with replacing all of that paper with silicon semiconductors that currently require clean rooms for manufacture.

              Much better solutions [sfgate.com] are coming online. Like hydrogen-pr
        • by quanticle (843097)
          The problem with thorium, as with all nuclear fission, is that eventually you'll still get waste that's unusable for energy production, but still emitting enough radiation to be dangerous. As the waste sits in this phase for quite a time (I've heard spans on the order of centuries) you have to find landfill locations that are stable enough to hold spent fuel for extremely long spans of time. Its the lack of space to store waste, rather than lack of fuel that's the limiting factor with nuclear fission.

          With
          • Re: (Score:3, Informative)

            by barawn (25691)
            That's not exactly true. The ideal output of most fusion cycles is stable. You get side production of tritium and a few other radioactive isotopes, though.

            But fusion does, however, produce a large amount of radioactive waste. Not through the products of the reaction. Through the byproducts of the high level of irradiation.

            The difference is that fission radioactive byproducts are long lived. Fusion radioactive byproducts are extremely radioactive, but very short lived, and therefore easier to deal with
          • Re: (Score:3, Informative)

            by rossifer (581396)
            Almost all of the waste from a molten salt Thorium fuel cycle reactor has a half life of 30 years or less (total storage of 300 years and it's as clean as the thorium ore it came from). Also, the mass/volume of the waste to be stored is substantially lower than a light water reactor because you can continuously mechanically and chemically extract the waste from the liquid fuel. With a solid fuel reactor, the waste is physically tied to 90% of the still-good U235 and the now damaged ceramic that makes up t
          • by ttfkam (37064)
            http://www.cosmosmagazine.com/node/348 [cosmosmagazine.com]

            Some of the main benefits of thorium reactors are that they vastly reduce the amount of waste, emit waste that has much shorter half-lives, and (here's the kicker) can eliminate existing stockpiles of plutonium and spent fuel.

            Fusion does nothing to address the issue of existing nuclear material.

            It's not an either-or deal; it's a measured "both."
        • Re: (Score:2, Informative)

          by Your.Master (1088569)
          Advantages of Fusion:

          * Fuel for fusion can be extracted from water, including non-potable water. Fission requires Uranium & Thorium to be mined and transported, and your country might not have it. By the time the fuel runs out, our sun will be a red giant, so we should worry about escaping the solar system before doing any better than that.
          * No weapons material generation (Thorium is in some respects similar here).
          * Radioactive waste: there's a lot less of the stuff sticking around, and really no hig
        • Re: (Score:3, Interesting)

          by adrianmonk (890071)

          we need clean, non-polluting power that doesn't ultimately come from politically volatile parts of the world.

          I don't know if that will ever happen. With most sources of energy, the fuel is unevenly spread around the globe. And being some small country that has a huge reserve of some kind of fuel will tend to mess your country up in the same way that people who inherit a lot of money (and never have to work a day in their lives) get messed up.

          Trade doesn't always have to create political instability,

      • by mdsolar (1045926)
        You want to be careful with that stuff. There was a boy who built a breeder in his mother's shed in the ninties using thorium. He was arrested again at the beginning of this month for stealing smoke detectors. He does not look so healthy in his mugshot: http://freep.com/apps/pbcs.dll/article?AID=/20070 8 03/NEWS04/70803062 [freep.com]. Sad story. There just isn't any such thing as clean fission. It makes a mess every time.
        --
        Get clean energy: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]
        • Yow, what happened to his face? I think he should be stealing chemotherapy drugs instead of smoke detectors. I guess once you've made one reactor you just can't quit.
  • Oh, great! (Score:5, Funny)

    by Sloppy (14984) on Friday August 10, 2007 @06:05PM (#20190297) Homepage Journal
    I just bought a fusion reactor that uses the old design!
  • by Zarhan (415465) on Friday August 10, 2007 @06:13PM (#20190391)
    ...and as prototypes too.

    http://en.wikipedia.org/wiki/Stellarator [wikipedia.org]

    Anyway, basically what I know about this is that stellarator designs avoids lots of the problems that are present in Tokamak - namely, degrading of the reaction chamber due to escaped neutrons. A fusion reactor using stellarator instead of Tokamak would, in effect, last forever since the material does not become radioactive.

    Especially the Germans have been researching this stuff a lot, however, most of the big money is currently in Tokamak designs, including ITER. Which is kinda a shame - since we're not in the Manhattan Project-type "if you have 3 designs and think one of them might work, build all three, here's the money"-situation..so these nice ideas may only be developed further if Tokamak fails to become viable..
    • According to the comments at the end of the physorg article, that's not true.

      Also according to those comments, the idea of fusing atoms is completely unproven.

      I think I'm just going to give up on humanity.

      • by kravlor (597242)

        Sorry, but fusion works. It is completely proven as a physical mechanism -- look at the Sun! Look at the fusion reactors in which we've generated hundreds of megawatts of fusion power (not breakeven conditions); look at particle accelerators...

        So, keep your faith in humanity; just because some ignorant asshat wants to blurt blatantly incorrect things like "water isn't wet" or "gravity doesn't work" doesn't mean it's true.

        • by Grishnakh (216268)
          Yes, I know fusion is proven, that was my point.

          But it doesn't seem like it's just a few ignorant asshats blurting blantantly incorrect things, it seems like it's most people. After all, look how many people go around saying evolution is false and the earth is 6000 years old. Even here on Slashdot, a geek haven, there's tons of them. No one understands, or even wants to understand basic science any more. I think we're headed into another Dark Ages.
    • Right. The slashdot summary is faulty: What's new isn't the stellerator design itself, but a new coil configuration for a stellerator. The new configuration "generating an external magnetic field designed to prevent the plasma from deteriorating", although I'm not familiar enough with stellerators to know how much of a problem this was in previous designs.
    • Anyway, basically what I know about this is that stellarator designs avoids lots of the problems that are present in Tokamak - namely, degrading of the reaction chamber due to escaped neutrons.

      So, where in the stellerator design does the unobtanium shielding goes that stops the neutrons?
       
      This is a serious question. If you have [hot] fusion you have neutrons, and they have to go somewhere. Magnetic fields won't stop them.
      • by sanman2 (928866)
        NEUTRons may be NEUTRal in terms of ELECTRIC CHARGE, but as fermions they do have magnetic spin, which means they are NOT IMMUNE to the effects of a magnetic field.
        • No, they are not immune to the effects of a magnetic field. Nor however are they easily effected by them. But that has nothing to do with my point - the fusion inside a Stellarator *is* going to generate neutrons, and those neutrons have to go somewhere. They can't simply be trapped forever.
  • Doh! (Score:5, Informative)

    by the eric conspiracy (20178) on Friday August 10, 2007 @06:15PM (#20190407)
    A stellarator is not a new design. The first examples were built here [pppl.gov] in 1951.
    • by pontifier (601767)
      Seriously, who's never heard of a stellarator before? Certainly anyone who's truly interested in fusion power has read about them.
  • by viking80 (697716) on Friday August 10, 2007 @06:21PM (#20190485) Journal
    Design parameters for fusion reactor:
    1. Contain a plasma ball with high density for fusion reaction. Ball is much better than doughnut if you just can figure out a way to keep the plasma together.
    2. Make a wall that is far enough away to not melt from this plasma ball to absorb heat/radiation to make power, and keep it close enough to get high enough energy density on its face.
    3. Make the wall 1 ton/m^2 to protect the people outside
    4. Use magnetic field outside plasma ball to contain radiation.

    This seems like a tall order, and it is, but consider the sun/earth:
    1. Gravity works great compared to magnetism.
    2. Well, here on the earth, it is 1kW/m^2. That is much higher than the energy consumption in most cities. Should be good.
    3. Our atmosphere stupid.
    4. The earth again has a great magnetic field that protects us pretty well.

    Bottom line: Why reinvent the wheel?
    • by OeLeWaPpErKe (412765) on Friday August 10, 2007 @06:32PM (#20190587) Homepage
      4. Use magnetic field outside plasma ball to contain radiation

      This seems like the exact reason why basic physics should be mandatory in schools. Dear God. How exactly would a magnetic field contain neutral photons ? They will generate zero flux and will not interact with the field at all.
      • Re: (Score:2, Funny)

        This seems like the exact reason why basic physics should be mandatory in schools. Dear God. How exactly would a magnetic field contain neutral photons ? They will generate zero flux and will not interact with the field at all.
        Clearly adding a flux capacitor to the magnetic field generator is necessary to add flux to the contained photons.
      • Re: (Score:3, Insightful)

        by lawpoop (604919)

        This seems like the exact reason why basic physics should be mandatory in schools.
        Okay...

        Dear God. How exactly would a magnetic field contain neutral photons ? They will generate zero flux and will not interact with the field at all.
        Is this the kind of basic physics that the average student would understand in their mandatory class?
        • by hab136 (30884)

          Dear God. How exactly would a magnetic field contain neutral photons ? They will generate zero flux and will not interact with the field at all.

          Is this the kind of basic physics that the average student would understand in their mandatory class?

          The fact that protons are positive, electrons are negative, and neutrons are.. you know.. neutral and therefore not affected by magnetic fields.. yes, I learned that in about 6th grade.

          • Re: (Score:3, Informative)

            by rossifer (581396)
            Actually, you'd be correct if you were to say that neutrons are not affected by electric fields. But neutrons are fermions with magnetic spin and are affected by (and can be moved around with) magnetic fields, so...

            Regards,
            Ross
        • If we're dealing with fusion, what are the effects of mass amounts of neutrinos going through living tissue?

          You know, 1/d^2 is sort of a problem when you are d close to me. (When d is is 1/500 AU).

          And yes, I do know about the super-pure H2O and Cl- deep-mine tanks that monitor for neutrinos.
      • by Aqua OS X (458522)
        I took physics in high school and I still have no idea what you're talking about.
      • 4. Use magnetic field outside plasma ball to contain radiation

        This seems like the exact reason why basic physics should be mandatory in schools. Dear God. How exactly would a magnetic field contain neutral photons ? They will generate zero flux and will not interact with the field at all.

        Please reread parent post. Note: 1 ton/m^2 of mostly Nitrogen *and* magnetic field to protect people.
        Life on earth has pretty much evolved around surviving radiation not caught by this protection. The physics is sound.

      • by qbwiz (87077) *
        Not all radiation is made of photons. Specifically, alpha rays are made of helium nuclei (and are therefore positive) and beta rays are made of electrons (and are therefore negative).
      • by mdsolar (1045926)
        Radiation is not just photons. There is a good point here. While there are very few nuclear reactions going on on the surface of the Sun, mainly spalations from accelerated protons, there are accelerated protons from the corona (the same) that impinge on the Earth's magnetosphere and are deflected. It is the Sun's magnetic field, rather than escaping fusion products, that are responsible for the high energy particle flux.

        There are also possible photon-magnetic field interactions though with a low coup
    • Re: (Score:3, Funny)

      by Wonko the Sane (25252)

      3. Make the wall 1 ton/m^2 to protect the people outside

      Houston, we have a unit problem
    • by mako1138 (837520)
      We're not reinventing the wheel. The sun's fusion reactions are very different from the ones envisioned for terrestrial fusion reactors.

      The sun starts by fusing hydrogen. (http://www.tim-thompson.com/fusion.html)
      This first step happens on a huge timescale:

      p + p --> d + e+ + nu 7.9 x 10^9 years

      This only works out in the sun because it's a frickin huge ball of gas.

      Terrestrial reactors will use DT fusion. The time it takes for this reaction to happen is not worth talking about.

      And regarding the
      • by rossifer (581396)

        Terrestrial reactors will use DT fusion. The time it takes for this reaction to happen is not worth talking about.

        Actually, He3-He3 fusion (the last few steps in solar fusion) is substantially safer than DT fusion due to the minimal neutron flux. See wikipedia [wikipedia.org] for more information (it's the last reaction in the proton cycle where 2 He3 -> He4 + 2 H- + 12.86MeV). Not quite as much energy as D + T -> He4 + N + 17.6MeV, but still a respectable amount of energy and much less neutron damage to the reacto

        • by mako1138 (837520)
          He3+He3 fusion on Earth, seriously? I don't think that's a realistic fuel; the reaction cross-section is extremely small, even at solar temperatures. Nobody talks about doing He3+He3 fusion. Are you perhaps thinking about D+He3 fusion?

          D+He3 fusion (and other aneutronic fusion, like p+B11) certainly is nice, but we're not going to get there anytime soon. Why? These fuels don't "burn" easily; the cross-sections for aneutronic fuels are lower than DT's, and peak at substantially higher temperatures. I suspect
    • Honestly, how is this insightful?

      Your answer is "we should use the sun". Well done. Got any better methods than what we're using currently?

  • "The holy grail of fusion reactors has always seemed 'just a few years off' for many decades. But a recent design enhancement termed a 'Stellarator' may change all that.


    Practical uses of Stellarator technology are projected, of course, to be "just a few years off".
  • Quasineutrality? Quasi-likely-to-work-in-the-real-world more like. :P
  • by flickwipe (954150)
    Refrigerator full of Stella?
  • If society won't even accept safe fission designs, what makes you think we will ever get far more powerful fusion reactors built? I think the largest problem now is the culture of misinformation and fear, not the problem of technology.

    Unless I'm wrong, the production of non-military nuclear reactor designs in the US for the last 30 years have been... zero. Unless you count the Galileo, Ulysses, and Cassini space probes. Call me when we upgrade all of our reactors from 1973 designs [wikipedia.org] to a much safer and cleane
    • by mdsolar (1045926)
      Gen IV does not finish design for 25 years. The new reactor that is moving forward the fastest is Calvert Cliffs 3, a run-of-the-mill light water reactor. I suspect this one will have trouble. While the nuclear power industry is talking about global warming all the time now, they seem pretty foolish to be betting on a sea level reactor as their first new project since the Three Mile Island and Chernobyl disasters made clear what a problem nuclear power is. The rise in sea level is 5 cm every 15 years an
    • Doesn't the Z machine require vast amounts of electricity just to "fire" once? They only fire it once or twice a day at MOST and it fires for only billionths of a second. It's not a continually running thing. It also produces a shockwave something like a mini-earthquake when it fires.

      Also look at this link: http://www.sandia.gov/media/z290.htm [sandia.gov]

      "Stockpile stewardship" is not about solving our energy problems... Well, at least not peacefully... It's all about ensuring that the aging nukes will perform
    • Fusion reactors produce a whole lot less radioactive material as they run. Fission reactors make lots and lots of really hot stuff. Also, as people should take away from the article, fusion is really hard to keep going. If things get out of hand, it will just go out. No melted cores. No burning reactors dumping tons of highly radioactive material into the atmosphere and into the surrounding environment. And the whole process of refining reactor fuel does not create mega-tons of radioactive mine tailings, to
  • Why not just a sphere ????
    • Because it's horribly complicated to create a spherical magnetic field to contain Plasma in it. You probably had Maxwell's equations in college? The divergence of the magnetic field is zero, thus magnetic field lines always have to be closed. It's topologically really hard to build a spherical field out of that.
    • by kravlor (597242)

      Short answer: because it's been proven to be physically impossible in any topology which can be mapped to a shpere since the 50's, at least if you're confining with magnetic fields. It has to do with their structure.

      That's why all devices are topologically similar to that of a donut, be it like an inner-tube shape (tokamak), cored apple (spherical tokamak), or funny twisted kinky looking (stellarator).

      The main difference between the tokamak and stellarator is where to supply the confining magnetic field.

  • by Ungrounded Lightning (62228) on Friday August 10, 2007 @10:55PM (#20192379) Journal
    I seem to recall one of Bussard's points in his talk Should Google Go Nuclear? was that plasma confinement by magnetic fields is inherently unstable when the confinement is concave toward the plasma, no matter how you twist them. Thus Stellarators, Tokamaks, etc. are (in his opinion) doomed. (And that's why his design is conVEX toward the plasma.) [google.com]

    (My take on that has been that even if passive geometries are unstable, if you can get it stable enough that instability growth occurs at no more than an HF rate you might be able to use an active system to finish the job of stabilizing the confinement. But that's a separate issue.)
  • PNAS does not post papers in review on its web site. This paper was PUBLISHED online on July 17th.

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