Building your own Star

There are very few sources of truly clean energy out there. Coal, oil, natural gas, etc. all expel tremendous amounts of carbon dioxide into the atmosphere, something we know we need to stop doing very soon if we want our planet to be habitable to humans for very much longer. Biofuels, while not as harmful as fossil fuels, still emit tremendous amounts of carbon dioxide, and are not a long-term solution. Modern nuclear power produces low amounts of carbon dioxide, but significant amounts of radioactive waste, which isn't good for anybody! Even hydroelectric power has disastrous environmental consequences, destroying entire river ecosystems downstream of wherever the dams are built.

But there is an abundant source of power that is free to all and free of pollution. I refer, of course, to the Sun. The Sun bombards the Earth with visible light, infrared heat and ultraviolet radiation continuously, providing us with a constant and tremendous source of energy.

If we could create this same energy source here on Earth, we would have virtually limitless, pollution-free energy. Let's look into how it works. The Sun is a giant ball of (mostly Hydrogen) gas. For that matter, so are the four largest planets in the Solar System. What's the major difference between the Sun and Jupiter, Saturn, Uranus, and Neptune?

Size. The Sun is 750 times as massive as those four gas giants combined. The pressure generated at its center is incredible -- about 250 billion times what the pressure is on Earth, or about two billion tonnes per square inch.

The pressure is so great at the center that it can cause nuclear fusion, the reaction that takes protons, neutrons, and light nuclei, and combines them into heavier elements, giving off a tremendous amount of energy in the process. The most energetic bombs in the world -- H-bombs -- rely on nuclear fusion.

But bombs are completely uncontrolled; there is no way to harness that energy to make it useful and usable for energy purposes. So how can we build a safe, efficient, but usable energy-producing mini-star on Earth? The National Ignition Facility in California has taken an old idea and is running with it: use lasers to compress a pellet of fuse-able materials!

The lasers they're using simply send out a short pulse of energy, compressing this pellet. There isn't even that much energy involved: 10 million Joules. That's about as much energy as you'll find in a very large, fatty (e.g., Waffle House) breakfast. Why is this so impressive? Because the energy is put out over a miniscule timescale, only 20 nanoseconds. If you convert that into "power", then for those 20 nanoseconds, you spend 500 trillion Watts, or 500,000,000,000,000 Watts! This is enough pressure, at the atomic level, to fuse the hydrogen isotopes inside into helium.

Each atomic fusion reaction releases a tiny amount of energy: about 2.8 trillionths of a Joule. But there are so many atoms in there -- around Avogadro's Number -- that you can get out even more energy than you put in! It's like making your own miniature star for a teeny-tiny amount of time.

The fusion that results is exciting because this will get us past the break-even point for the very first time using this method! This means we get more energy out than we put in! The products of this reaction? Helium and Hydrogen gas: completely benign. So not only is it possible to build your own star -- however briefly -- but this may also be the long-term solution to our energy problems! Now, if only we can figure out how to take the energy from these mini-explosions and put them to good use...


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It seems tricky in that a nuclear reactor relies on heat generated by the reaction to make water boil, generate steam and turn turbines. But fusion is complicated in that it requires intense heat to initiate and I suspect that requires some kind of intense magnetic containment. So how to do you capture the heat generated by the reaction and use it to boil the water?

It's perfectly clean, except for the pesky neutron.

This article made me wonder about electric generators,and magnetic fields, which lead me to an interesting way of viewing something, "the Earth is a global MHD dynamo."

Hmmm ...

The earth stays at a relatively constant temperature. The sun radiates energy onto the earth, and the earth radiates energy away. If the sun's power level increases, then the earth's temperature increases, and vice-versa if the sun's power level decreases.

Converting mass to energy via fission or fusion is, from an energy balance point of view, equivalent to increasing the sun's power level, in that it adds energy to the earth. So does the burning of fossil fuel in that energy which was put into the fuel long ago is released when it is burned.

So, how about providing a simple analysis of this? The burning of fossil fuels and the production of energy via fission and fusion is equivalent to a percentage increase in the power level of the sun, and thus contributes to global warming. What is that percentage?

While fusion is likely to be relatively clean compared to some of it's competitors, it's hardly perfectly clean. The easiest fusion reaction to ignite, by a fairly significant margin, involves deuterium and tritium, and produces high energy neutrons. Typically most of these neutrons will be absorbed by a shield of liquid lithium, but some portion of them will go in the wrong direction or otherwise not be absorbed, and will instead be absorbed by the structure of the reactor, possibly transforming a stable nucleus into a radioisotope. Reactor designs try to make sure that most new isotopes will either be stable or will have a short half-life (thus decaying to safely in a short time), but it's impossible to entirely get rid of this problem without using a different fuel.

Direct power production is unlikely to substantially affect the earth's temperature; somewhere around 0.01C per terawatt. More importantly, it isn't cumulative from year to year

So if even nuclear fusion is not 100% clean, what about wind power?

hypothesis: wind is already generated directly and indirectly from the energy received via solar radiation, so tapping it would not add any carbon output and therefore is clean?

By NewEnglandBob (not verified) on 26 May 2009 #permalink

Brando: actually, the point of this technique is that unlike the Tokamak reactor design, you don't really need magnetic containment. The latter works by taking (relatively) hot hydrogen and compressing it. The idea behind the laser technique is to start with a dense pellet of frozen hydrogen, and heat it up faster than it can expand. Thus the incredibly brief timescale.

Wind produces some conventional pollutants as part of the manufacturing process, and also produces its own special problems in terms of noise, disruption of air flow, killed birds, and so on. Solar likewise produces pollution in manufacturing, and disrupts the ecology of the area the solar plant occupies. There's really no way of producing power that doesn't disrupt something; it's just a matter of deciding which disruptions we can tolerate.

A tritium fusion plant would likely produce electricity by heating a lithium blanket, which is either used directly as a working fluid, or indirectly to heat water. Either way, it's basically a conventional heat engine.

Brando, Anthony:
If the process uses inertial confinement (as Laser processes do) then you can directly take energy from any charged particles coming out. Force the He4 nuclei to climb up a 1.75MV electric field to get out, and you've sidestepped the need for a heat engine.

You'll still want a heat engine for the energy in the neutron, but since you loose energy breeding more tritium, and converting heat to electricity is hard, you only get about twice as much electricity from the neutron as the He4 nucleus, even though it has 4 times the energy.

Wind has more pressing issues with scaling and diffuseness. On large scales, each wind farm isn't independent, and so you need 10-20x overcapacity, or alternatively the ability to store 2-3 weeks of energy supply for the country. Both are difficult. There are related issues with reliability of supply; countries with substantial renewable usage routinely use their neighbours as reliable backup. (eg. German wind falls back on French nuclear)

How about we catch a lightning bolt and use the energy to fire up a self-sustaining fusion reaction?

Problem 1: Predicting where the next bolt will strike...
Well some areas are more prone to electric storms, so start there and go fishing with a decent copper rod.
OK, maybe the chance of a strike is still too low?

Problem 2: Containing the energy in the strike...
From the rod, direct it straight into the fusion cell, have the isotopes ready to go.

Problem 3: Sustaining the reaction...
Immediately fusion starts, divert some of the resulting power back to fuel the containment system sustaining the reaction.
What have I missed?

If there's a neutron coming off, could we use that to make normal hydrogen into deuterium or tritium, thus increasing the amount of fuel we have?

I second Boronx. The health physics implications of fusion are not trivial.

Jonathan: interesting comment! I hadn't actually been aware that you could extract energy from the charged particles. That's pretty cool.

By Mister Troll (not verified) on 26 May 2009 #permalink

Is there enough lithium to make this a long term energy solution? My understanding (from things I've read having to do with lithium batteries) is that while lithium itself is fairly common, useful lithium ores aren't.

I think the best way to harvest energy from this sort of reaction is to build a giant internal combustion (read fusion) engine where the heat of the reaction is used to expand regular matter (maybe liquid nitrogen) inside of a large cylinder to drive a piston, turning a crank and driving a giant dynamo. You'd need a power take off to compress air into a liquid or a solid and you would need some of the resulting electrical energy to drive the laser arrays, plus whatever energy you need to make the deuterium and tritium fuel pellets. If you find efficient ways to do all that and someone runs the math and finds a good net gain, then it just might do the trick. Best of all, it's just a ramped up version of an extremely common technology and gets around that pesky "we can blow stuff up with it, but what else is it good for?" problem that we have with the H-bomb.

This was something that my old roommate and I disagreed on utterly. She somehow couldn't get past that it wasn't 'natural', despite my insistence that the nuclear reactors are similar to miniature stars and that naturalism has nothing to do with this. (That truly, nuclear fusion the cleanest form of energy we could use (albeit a little difficult to perfect on such as small scale). (Although I have large issue with the term of 'natural' to begin with.)

While I must say that I do not have much knowledge with nuclear reactors, but nuclear fusion in stars was the first thing we learned in my astrobiology class.

I really enjoyed reading this post, especially the opening paragraph. I think you omitted one very important energy source: the sun itself. Sure, we can create our own sun for energy, and maybe someday that will be feasible. However, let's not overlook the fact that 1366 Watts per square meter of the sun's energy fall on the Earth. It's already there. All we need to do is harness it. I honestly think the ideal energy sources are solar, wind, geothermal, and tidal. The more "industrial" production of nuclear fusion may one day play an important role too, but not yet.

I guess the question becomes, will it turn out to be more efficient to build our own fusion reactors, or to go big harnessing that existing one in the sky with massive, space-based solar arrays that transmit power to earth in microwave beams?

Really, though, we just need to be advancing on all fronts. Either of the above are too far off still to be of use "very soon", as you point out is when we need to do something about greenhouse gasses. Biofuel is one very good solution. I mean, burning it emits CO2, but unless I'm on crack, that carbon mostly comes from the air when we grow the plants that turn into biofuel. (Plants aren't nuclear reactors, so it's gotta come from somewhere.) That makes it effectively carbon-neutral. Conventional solar and wind are great, as is small hydro. I'm in favor of nuclear, as well, since the waste isn't THAT hard to contain (and newer reactor types like the pebble-bed make it easier).

Fortunately, it seems like lots of advancement IS being made on all these fronts (as well as attacking it from the other end with increased efficiency in our devices that use the energy).

Biofuel is one very good solution.

While you're right that it's medium-term carbon-neutral, it's a lousy solution because it can't get anywhere near the required scale, unless you fancy turning a large chunk of the planet's agriculture over to fuel and letting half the population starve.

"Even hydroelectric power has disastrous environmental consequences, destroying entire river ecosystems downstream of wherever the dams are built. "
What have happened recently_
The scientists in Switzerland discovered that the artificial lakes created by the dams are producing incredible amounts of methane, in hundreds of tons...

we need to BURN H2O, its clean, and we have plenty of it on our planet: and its recylable, break it down into its costituants, hydrogen and oxygen (by electrolisis) mix it in a combustion chamber, and we have clean pure energy. lithium batteries are the go. deep cycle, running off a braking systemn give us the power to recharge the battery that gives us the power, to break water down to its components.its a beautifull way to clean power i want to experiment with this,LOVE MY PLANET