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New 'Stellarator' Design for Fusion Reactors
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."
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.
Does anyone know any more about this?
A-Bomb
Picture Chinese handcuffs
I just bought a fusion reactor that uses the old design!
As copyright owner of this comment, I authorize everyone to defeat any technological measure which limits access to it.
...and as prototypes too.
http://en.wikipedia.org/wiki/Stellarator
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..
A stellarator is not a new design. The first examples were built here in 1951.
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?
don't cut it off www.mgmbill.org
Related links: * LDX@MIT
* Physics of magnetically confined fusion [pdf]
* The main principles of magnetic fusion
* Magnetic fusion experiments at LANL
* High density magnetic fusion
* Has a good bit on magnetic confinement
* Can a magnetic field be used to contain plasma?
* International Thermonuclear Experimental Reactor
* What's happening in fusion?
* Design of magnetic fields for fusion experiments [pdf]
* Wikipedia article on the topic
* Magnetized target fusion bibliography
* Plasma physics bibliography
* Databases for plasma physics
* Plasma physics laboratories
* List of plasma physicists
* Plasma on the internet
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.
"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.
Sig free's the way to be.
Blast radius my foot. A fusion reactor is immensely safer than a fission reactor. Furthermore, fission reactors are really very safe (far safer than, say, oil refineries). Even Chernobyl was primarily a /chemical/ explosion (although caused by problems with the reactor), which happened to scatter radioactive debris over half the globe. A chemical explosion at a fusion plant would scatter hydrogen. Oh boy. Even the unstable isotopes of hydrogen are still light enough that they would float to the top of the atmosphere and escape into space in very little time. A fusion reactor is not a controlled H-bomb. Unlike a fission reactor, which requires a carefully tuned reaction to walk the knife's edge between dying out and going critical, the hard part with fusion is keeping it going. Fusion is very fussy. If the density, and the temperature, and the composition of the plasma are not just exactly right, then reaction dies out in a fraction of a second, the time it takes to exhaust the really tiny amount of fuel that is available to it at any given time. To keep it going, you have to keep feeding it more fuel, as well as carefully tuning things. If there were even a very very tiny explosion, the worst it would do is damage the devices tuning the plasma's parameters, and then the reaction would die out. Even if the fuel feeders went crazy and started flooding hydrogen in as fast as they could, it would still just die out. There is no way that the reactor, even in an undamaged state, could bring enough hydrogen to the needed density and temperature quickly enough to cause a thermonuclear explosion even on the scale of a pipe bomb. So, I say, blast radius my foot, unless you want to compress the researchers down very very small and put them inside the plasma itself.
Researchers are not involved in corner cases that might never happen. Nor are they worried about reliability yet (in the sense of preventing another Chernobyl, as opposed to the sense of very little downtime). They are just trying to get the blamed thing to produce enough energy to sustain itself, with some left over. (Although, if you're feeling pessimistic enough, you might call that a corner case that might never happen!)
I agree that we need to get a lot of funding to fusion research, but throwing money at the problem won't necessarily solve it. It is a very hard problem. Furthermore, we'd need not just one crazy (I presume you refer to the office of the President), but a whole bunch of crazies (half of Congress), because Congress makes the budget.
SIGSEGV caught, terminating
wait... not that kind of sig.