New 'Stellarator' Design for Fusion Reactors 171
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."
Stellarators aren't new (Score:4, Informative)
Doh! (Score:5, Informative)
Magnetically confined plasma fusion reactors (Score:5, Informative)
* Physics of magnetically confined fusion [ipp.mpg.de] [pdf]
* The main principles of magnetic fusion [www-fusion...que.cea.fr]
* Magnetic fusion experiments at LANL [lanl.gov]
* High density magnetic fusion [ucsd.edu]
* Has a good bit on magnetic confinement [geocities.com]
* Can a magnetic field be used to contain plasma? [anl.gov]
* International Thermonuclear Experimental Reactor [iter.org]
* What's happening in fusion? [ieee.org]
* Design of magnetic fields for fusion experiments [columbia.edu] [pdf]
* Wikipedia article on the topic [wikipedia.org]
* Magnetized target fusion bibliography [lanl.gov]
* Plasma physics bibliography [wisc.edu]
* Databases for plasma physics [weizmann.ac.il]
* Plasma physics laboratories [pppl.gov]
* List of plasma physicists [wikipedia.org]
* Plasma on the internet [weizmann.ac.il]
Re:Why reinvent the wheel? (Score:5, Informative)
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:Stellarators aren't new (Score:5, Informative)
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?"
Re:input-output (Score:5, Informative)
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.
Re:input-output (Score:5, Informative)
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.
Re:Thorium reactors (Score:4, Informative)
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.
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Go solar the easy way: http://mdsolar.blogspot.com/2007/01/slashdot-user
Re:Thorium reactors (Score:3, Informative)
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:Thorium reactors (Score:2, Informative)
* 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 high-level waste at all. This can save a lot of money with disposal and some with safety equipment, not to mention avoiding the headaches of dealing with people who believe that radioactive waste should not be produced at any cost. Note that this is actually partly a problem, since many nuclear "waste" materials have important industrial and medical uses, so we will likely continue to run some of these fission reactors anyway (or perhaps figure out ways to produce these radioactive isotopes more directly).
* Although fission plants are perfectly safe, there are a lot of people who still fear them for a variety of reasons, mentioning any of which is likely to lead to a fruitless and flame filled side-discussion if anybody reads my post at all. Fusion power is inherently even safer, which might satisfy a few of these people.
Re:Thorium reactors (Score:3, Informative)
Because the waste from a liquid fueled reactor can be continuously extracted in very small quantities, it's fairly easy to make uber-safe small containment vessels and constantly courier it to your long-term storage site. (a 1GW reactor would produce less than a half liter of waste product per day so you could make each container hold 100cc of the stabilized waste products and only need a modified armored vehicle to safely transport the five uber-bottles each day) With solid fuel reactors, you have large refueling events that generate multiple tons of waste per event. The quantity that must be managed at once makes it that much more dangerous to handle and transport safely.
Another nice thing about molten salt reactors is that they can be 97% fuel efficient. Unlike our current light water reactors which only burn about 10% of the fuel before the solid fuel is too contaminated with reaction poisoning fission products to keep an efficient reaction going any more. This efficiency is mostly due to on-site constant fuel reprocessing. There's an alternative molten salt reactor approach that doesn't involve reprocessing that is about 50% fuel efficient but gives you a lot of crappy waste every 20 years. I prefer frequent small quantities myself...
Possibly the nicest thing is that if you use a dual fuel configuration (a LiF/BiF2/UF4 kernel and a LiF/BiF2/ThF4 shielding/breeding layer) the core is thermally self-limiting. As the reactor heats up, the salt mixture expands and reduces the reaction rate until the whole thing stabilizes around 1500-1900C (the final temp depends on the exact fraction of UF4 in the mixture). You don't need control rods or any of the additional equipment to maintain moving parts in the reactor. All you need are pumps to cycle the kernel fluid and the primary cooling fluid and if those shut down, there's nothing to go wrong. The whole thing heats up and sits there radiating heat. If you want to put an automatic stop to the heat, put a thermal plug in the bottom that will melt if primary cooling ever stops and drain the whole core into subcritical storage containers underneath the core.
One big problem with the molten salt reactor is that the existing nuclear equipment industry makes most of it's money from fuel manufacturing. Molten salt reactors are constantly reforming the liquid fuel on-site, which means that the existing nuclear infrastructure has to change their business model (or be supplanted) before it can possibly work.
The other huge problem is that most of the advantages of the Thorium fuel cycle come from the fact that it's a breeding/reprocessing cycle. Both of which (fuel breeding and fuel reprocessing) are currently illegal in most first world countries due to nuclear proliferation concerns. Laws can be changed, but governments would have to be reassured about the risks. The thorium fuel cycle can be spiked with U232 which will prevent the creation of nuclear bombs (because U232 decays into a hard gamma emitter that destroys nearby electronics), but wouldn't prevent the construction of radiological "dirty" bombs (basically what Korea can build right now).
Ultimately, the big advantage of newer fission reactors over fusion reactors is that we can build the fission reactors today. Further, if we decide to breed fuel, there's enough known U238 and Th232 in the upper crust to prov
Re:Why reinvent the wheel? (Score:3, Informative)
Regards,
Ross