Slashdot Mirror
Fusion Gets Closer With Magnetic Field Correction
jparadise writes: "Seems folks over at the
the U.S. National Fusion Facility in San Diego have figured out a way
to fiddle with magnets to contain plasma and make their scale-model fusion generator produce energy significantly in excess of what they're putting in. It's not the final answer, doesn't look like, but it seems (maybe? hopefully?) like a step in the right direction ..."
What about the supply of deuterium? It's not perpetual...
It's close enough to perpetual that it makes no difference.
About 1 hydrogen atom in 7000 is deuterium. Hydrogen accounts for 1/9th the mass of water, which means that the mass of deuterium we could extract from the oceans is about 1/63000th the mass of the oceans.
Assuming an average depth of about 3km and a coverage of 2/3 of the Earth's surface, you have about 1e18 tonnes of water on the planet. Let's say 1e-5 of that is deuterium that you can easily extract, and you get 1e13 tonnes of deuterium.
Fusion is about 1% efficient at turning mass into energy. Let's say that your fusion reactor is 0.01% efficient in total (pessimistic estimate). This gives about 1e13 J/kg, or 1e16 J/tonne.
The total amount of energy we could extract from fusing the oceans' deuterium with these fairly inefficient fusion plants is about 1e29 J.
If we want our fuel supply to last a million years, that gives a world power consumption of 3e15 watts. Far, far more than we consume now.
If, within the next million years, we build reactors good enough to fuse light hydrogen, we'll have enough fuel to last us until the sun burns out (several billion years). Or we could just ship in deuterium from elsewhere in the solar system. Either way, barring a *huge* population expansion, we won't run out of power - ever.
In other words, either we get cheap, clean, nearly free unlimited energy, or our future is gonna look uncomfortably like those Mad Max movies.
Actually, what would be more likely to happen is a slow and painful shift to renewable forms of energy and a lifestyle that consumes less power.
Fossil fuels won't run out all at once - they'll get incrementally more expensive as they become scarcer and more difficult to extract. As price climbs, people will out of necessity start using less power, and alternative forms of power generation will become cost-competitive (even if their own cost doesn't change).
You'll see more houses with photocell shingles. You'll see a mirror-based heat plant or a wind farm next to most cities. More people will take public transit, because it's cheaper than driving. House design will depend more on passive heating/cooling and good insulation than on furnaces and air conditioners (they'll still be used; just on lower settings). People will have to hang-dry their clothes instead of tossing them in the drier. And so forth.
A Mad Max style catastrophy would only happen if energy supplies ran out all at once. A nuclear war or an asteroid strike could cause this, but I doubt fossil fuel problems will.
ok, so you have this plasma "floating" in the bottle at 12 gazillion degrees. the power goes out. doesn't your ball of plasma just eat it's way through anything it touches and head towards the center of the earth?
The plasma is very hot, but also very tenuous. You might have a few thousanths of a gram of matter in the reactor. As soon as this touches the reactor wall, it cools down to room temperature. Your reactor wall gets warm. That's about it.
Also, as your plasma is much less dense than air, if anything, a ball of plasma would rise.
You'd never get a ball. What happens is that as the containment field weakens, the donut-shaped mass of plasma expands until it touches the side of the container. In theory, if you had a "hole" in the containment field instead of the whole thing weakening, you could get a jet of what looks like flame, but this is next to impossible to do even if you're _trying_. The natural shape of the field is more-or-less uniform.
Plasma is just a hot, conducting gas. It follows gas law like everything else.
This site gives a general overview of current fusion studies.
For the more technically inclined, you can check out the journal Fusion Engineering and Design (Sorry - if the link doesn't work for you, it's probably a pay-per-access journal and your business/school/self isn't a subscriber). Anyway, it's full of juicy fusion engineering and design details.
I post this as a former fusion researcher and a former project manager for the Office of Fusion Energy (OFE) of the Department of Energy (DOE)
Many decades ago the international fusion community put all of its chips on the Tokamak. It has been a disaster.
Even if a Tokamak could produce break-even fusion ( getting more energy out than you put in) the engineering obstacles to creating an economically successful reactor are daunting.
Many years ago, the OFE sponsored a study, Project Aries, of the costs of a Tokamak reactor. Even using the usual optimistic assumptions, the cost came in way above solar and wind power, let alone fossil fuels.
Another symptom of the problem is that three times in a row, projects to build larger Tokamak have collapsed in the design stage. That is, even before anything was build, none could come up with a working design. The International Thermonuclear Experimental Reactor (ITER), the latest attempt, collapsed as the price tag spiraled above $20 billion (US)
The whole OFE degenerated into a "you scratch my back and I'll scratch yours" process where the lab directories divvied up the pie. All non-Tokamak ideas were cut off, including the one I worked on.( more below).Congress cut the OFE budget almost in half a few years ago in response to this.
That being said, I respect the findings of the DIII-D team. The DIII-D is very well run research project, the their accomplishment is to be applauded. Now for a blatant plug. In the 70s I worked on a small project at the University of Miami, the Trisops project, which was defunded. The amount of money was not an issues ( our request was quite small), but the non-Tokamak nature, and the nerve of the principal investigator, Dan Wells, to point out that the Tokamac was unworkable.
The Trisops machine was recently moved from the University of Miami, to Lanham Md, with a small NASA grant, but there is not money to run it. You can see a report on it.
Another interesting project, the Plasmak(TM) project that is being run by Paul Koloc ( out of his garage!!).
The holy grail on fusion research is a stable plasma structure. The Trisops project achieved it one way. Paul has noted that ball lightning, which has been known for millennia, is a stable plasma structure. He has machine that produces ball lightning, and is measuring it. He gets no DOE funding of course.
I know it is theoretically the perfect power source, and that it shouldn't produce environmental problems like nuclear waste or dirty emission - but I also know as-sure-as-eggs-is-eggs that there is going to be a protest movement against it, regardless. Which leads me to my question...
Are there any fusion protest groups yet? I'm always late to join protest movements so I get crappy seating at rallies and never get to talk to the news media about my important opinions on the subject.
If you know of any, please post. If it helps, I am SINCERELY against the late 60's musical movement by the same name.
(signed, someone who genuinely wants to make a difference, as long as others are watching...)
IANAP, so I am talking out my ass here, but it seems to me that the interior surface of the container of a reaction might just somehow be able to more directly collect energy, similar to the way solar-panels collect light. Of course, I have no idea what kind material might be used to accomplish this. How do solar-panels work? Silicon? Is it just dumb luck that the elements of a solar panel happen to convert light to energy, or is it a man-made composite, built specifically for that purpose?
... fusion reactor vessels will likely not be cheap).
... collisions ...). By that time, all that the sun radiates is a near perfect blackbody radiation spectrum.
Yes, you are talking out of your ass.
Note: I did my Ph.D work in plasma physics but now I work in quantum and optical electronics. I am probably one of the better qualified people here to answer your question.
Conventional fusion reactors fuse deuterium and tritium. Or, if you breed tritium from a lithium blanket surrounding the reaction, you can do fusion using deutrium-deutrium full burn (this is tougher to do than D-T reactions).
However, the by-products of D-T and D-D fusion are mostly high energy neutrons (and some gamma rays and neutrinos and alpha particles...). High energy neutrons are not easy to convert into electricity because neutrons are not charged. In fact, the neutron flux of a large fusion reactor would be deadly and thus a fusion reactor needs to be heavily shielded while operating. (Watch "Chain Reaction" and laugh as Keanu and his advisor walk around the operating reactor after it stabilizes.)
A typical approach for the conversion consists of letting your neutron flux heat a block of lead (or other material) and then running a standard steam cycle.
This sucks on many levels.
First, you end up throwing away much of your power from the inefficiency of the steam cycle. That is the theoretical thermodynamic efficiency of a fusion reactor which can somehow do direct conversion is effectively 100% (hot reservior at millions of degrees, cold reservior at room temp) while a steam cycle is limited by how hot you can heat your materials (hot reservior at thousands of degrees, cold reservior at room temp).
Second, the neutron flux will activate (i.e. make weakly radioactive) the walls of your reactor and steadily degrade the structural integrity of your vessel. As a result, current estimates are that the core of a fusion power plant will need to be replaced every couple of years (which makes energy providers frown
Other approaches are to use fusion reactors as breaders for fission plants (i.e. use fusion neutrons to enrich fission reactor fuel). Many estimates already put current reactor technology beyond breakeven for this type of design. However:
- Design is not politically feasible (some alternative fission fuel cycles might be possible). Fission suffers from NIMBY and fusion-fission breeders have a massive proliferation risk.
- Fuel for fission reactors is not particularly rare and running a fusion plant will likely not be cheap. Thus, economically, currently there is no compelling reason.
Solar cells on the other hand rely on photons exciting electron-hole pairs in a semiconductor. The light from the sun partially consists of photons in the visible and near infrared range which are suitable for conversion by a solar cell.
You might be wondering why fusion reactions produce high energy neutrons and gamma rays and other generally nasty things while our sun shines a whole lot of light. You should remember that the sun is big and the products of a fusion in the sun take hundreds of thousands of years to reach the surface (random walk
A higher dependency on Solar Cells and heat-energy-converting/trapping devices could also help lower the amount of heat we have to deal with.
umm, these devices, which allow you to store heat energy only take heat out of the system until you actually use them, at which point they return all the heat they took originally.
Sure fusion may allow us to have access to alot more heat, but the stuff is quite willing to radiate off the planet with minimal fuss (Given proper atomospheric conditions).
Now turning our planet into a solar greenhouse or toxic waste dump- those are potential problems. "Heat Pollution" is a non-issue.
The tokamak reactor design uses a torus (donut) shaped ring to confine the plasma. Another design is one my (former) physics professor and the group he is in are currently working on. Basicaly the design consists of two magnetic rings, one above one another. The electric field is threaded through the bottom one and through the top one. The electric field bulges out between the two rings making a sort of "coat hanger" cross section between the rings. This forms the shape of the magnetic bottle.
Classical EM shows that the plasma particles will be confined to the electric field lines and helix around them. If there were no magnetic fields the particles would "escape" this system through the top and bottom of the E-fields.
The neat part is that when the magnetic fields change, the system imparts an angular momentum onto the plasma particles. The result is that the plasma spins (in the same plane as the magetic rings). Since the electric fields are in a bent, the centripetal force will push the plasma into the middle of the "bottle" and away from the top and bottom. The anaolgy he gave was take a bead and put it on the bent wire of a coat hanger. Now spin the hanger around its long axis. The centripetal force will push the bead to the "bulge" of the hanger. Similarly, the plasma should be pushed to the "bulge" of the magnetic bottle. Hopefully when enough energy is added to the system the plasma will fuse.
Last I heard the group this professor works in was trying to get funding to program a model of the reactor, so no working model is on the way soon. He claims that thoeretically this setup should be able to cross the energy in-energy out threashhold. Of course only time (and money) will tell.
From itercanada.com:
What about the risk of an explosion or meltdown? Is this possible with Iter?
No, the fusion process in Iter can only be achieved under precise, controlled operating conditions. If conditions in the Iter machine are not ideal, the process just stops - it cannot escalate out of control. Therefore, there is no possibility of a massive energy release-or a "core melt" accident-from the Iter Tokamak.
Basically, in order to keep the plasma going, it needs to be constantly controlled by the magnetic containment field. If this field fails, there's no explosion; the plasma effectively loses state, and the whole reactor shuts down of it's own accord.
In a nutshell, fusion energy is safer than breathing.
Obliteracy: Words with explosions
Actually, if you are quite close to the reactor when it fails, you are in some serious trouble. The plasma inside the Torus is at a very high temperature (I thought it approached Solar temps, but cannot confirm this). If it spills all over you, you are dead. I assume any commercial reactor would be contained in some way to prevent accidents of this sort.
You are right about the temperature, but containment is exactly the wrong solution. What you want is something that breaks away (in a controlled direction, say "up" would be nice). Remember that the quickest way to cool something really hot is to let it expand. (The second quickest way is of course to get venture capital.)
This applies to pretty much any concentration of free energy. You can burn gun powder safely in a small metal dish, but the same quantity in a small metal pipe makes a rocket or a bomb (or both) depending on how the ends are capped. With the plasma from a just-failed fussion reactor you're looking at something on the order of a lightning bolt. Set free, you have a big flash, a loud bang!, and a lot of people saying "What the fuck was that!?!?!"
Try to contain it, and you have a much louder boom, and a somewhat reduced number of people crying "Oh, the humanity!"
-- MarkusQ