|Posted by Craig on April 17, 2011 at 7:28 PM|
I have been considering fusion power.
For the uninitiated, Fusion is a type of nuclear reaction. Before you start throwing around words like Chernobyl and nuclear waste, let me make some definitions.
Current nuclear power plants utilise a process called Fission. This is what happens when heavy atoms, like Uranium, are split. A neutron (a normal part of atoms) is fired at a lump of Uranium. It hits one atom, breaking it in two and producing two more neutrons, which shoot out and hit two adjacent atoms and split them, repeating the process. This is what is called a chain reaction. The resulting atoms are the nuclear waste that people are so worried about. The other reason to worry is that the chain reaction cannot be controlled.
Fusion is the opposite. Light atoms get fused to produce heavy ones. This is different in that a chain reaction does not occur; if you want to stop fusing, you simply shut off the reactor. For the skeptics, there is currently one working fusion reactor: if it's daytime, you're sitting right under it. The sun is a fusion reactor. The other really nice thing is that it works best with light atoms, particularly elements with which the planet is choc-a-block packed. According to my research, a Boron-Hydrogen reaction produces about 17 electron volts of energy (thats a lot!). And what's more, even the simplest reaction (Hydrogen-Hydrogen) uses fuel that can be obtained straight out of the water. As for waste, have you ever been to a kid's birthday party and played with one of those balloons that float to the ceiling? The stuff in those balloons is Helium. That's the waste from most Fusion reactions. It is tasteless, odourless, and makes your voice sound funny. What's more, it has uses in industry, and is quickly broken down by UV light in the atmosphere. Tell me, how many power generation processes do you know of in which the waste products are already widely used in industry? I don't know of any.
If I have convinced the nuclear-phobic reader that Fusion is the ultimate green energy, then hopefully your next question is "Why aren't we using this stuff?"
A couple of reasons, actually.
One: Fusion is really hard to do. It is possible to construct devices which induce artificial fusion. These have been around for half a century. Just google the "Farnsworth-Hirsch Fusor.' The funny thing is, this kind of thing is a common high school science project, if you got a few grand lying around. The problem is actually creating a device which produces more energy than what goes in. If one with an engineering mind considers it, not even the sun does this. Over many billions of years, a gas cloud (a BIG one) condensed, gathering gravitational energy, until the temperature and pressure at the very centre became so high that the Hydrogen there began to fuse and release all the energy gained from gravity. I'll go into the math required later on, for now let's just say?the required temperature is around one million degrees and about a few hundred thousand times Earth's atmospheric pressure. The point is that the energy coming out of the sun has been building up for millennia inside the nebula that gave it birth. It's a lot like a battery releasing energy after a long charge up phase.
Two: It's kinda hard (IMPOSSIBLE) to get those pressures using the current science and technology. We can, however, get much higher than those temperatures, but it's butt-numbingly expensive.
That leads me to three: Economics. Producing high pressure requires large pressure vessels and lots of power. Generating high temperatures requires even more power. Generating power like that requires lots and lots and lots of money and resources. Currently the world is wrapped up in other economical disputes. We've got oil billionaires sucking the fossil fuels dry, soaring petrol prices, collapsing economies, two or more wars. We barely get the money for the International Space Station. So we can't really spare money to recreate the sun in a bottle, can we? The other problem is that research into alternative methods of fusion also costs a lot, and it's hard to find investors. Good luck getting governments involved, because they're already on the bandwagon of a development project based on high-temperatures.
This project is called ITER (International Thermonuclear Experimental Reactor). Have a look at the website http://www.iter.org/. It uses a design called Tokamak, which is essentially a donut-shaped reaction chamber. One of the main problems with fusion is that the fuel has to be so hot that no material can contain it. Instead, it is confined in electromagnetic fields. Since the fuel is plasma, it is positively-charged, and so will be forced into a small space by an appropriately designed electromagnetic field. The walls of the Tokamak are lined with coils which will produce a magnetic field. The reactor itself will be massive.? Let's just say that a tall man could stand upright in the reaction chamber. The magnetic fields will require huge currents to produce and the heating of the fuel much more energy to achieve. Not only that, but it seems they have no way of actually turning the energy produced into electricity for our TVs and Wiis. So about ten different countries are pouring billions of dollars into this project, which will NEVER be a viable fusion process. The physicists on the project openly state it won't work, but, hey!, it's very good physics. And we all thought the LHC was a waste of time (I certainly think so).
Fusion by heating would be a very good science project, and would probably help understand more about particle and plasma physics, but it won't be a new source of power. You'd always need to put so much more energy in than what comes out. I've known that ITER won't work for a while, ever since I saw that the design didn't seem to show any method of extracting electrical energy, which is what this whole thing is supposed to do. So I've looked into other methods of fusion.
Remember the Farnsworth Fusor I told you to google. A physicist, the late Robert Bussard, spent most of his life enhancing the design, and came up with a method of fusion called the Polywell. It's a combination of magnetic confinment (like what goes on in ITER) and inertial confinment techniques, to keep a plasma in a small vessel, and make it fuse. Google "Polywell" to get a look at some of their prototypes. They claimed that a Polywell reactor could produce net energy at a reactor size not much bigger than your car, and could be powered by the same energy that most fission power plants run on. Think about that: ITER is about as big as your school assembly hall, and won't produce net power; you could power your own home with a Polywell fusion reactor, and keep it in your garage!
ITER uses a reaction between Deuterium and Tritium. These are different types of Hydrogen. One is naturally occuring and is most likely in the bath water you used today. The other doesn't occur naturally, and needs to be manufactured in fission plants; also its radioactive. This reaction produces helium, and stray neutrons, kinda like the ones used to start fission reactions. Bussard's Polywell reactor uses normal Hydrogen and Boron as its fuel. Boron is an abundant plant nutrient, and is found all over the world. Ever used Borax and glue to make toy slime? Borax is an ore of Boron. And helium is the only resulting product.
Bussard developed and tested his design under a small U.S. Navy contract. They stretched their funding enough to push their work to the point that all the physics was sorted out, and all that remained was to engineer a working reactor. The latter is the easy part. The problem was that if the Navy gave them more money (as in $200M) to build a test reactor, it would show up on the Federal Budget, and the government would put an end to it since they're already involved with the really expensive yet totally worthless publicity stunt called ITER. So Bussard looked elsewhere for money. He even gave a talk to Google on the subject. Search the phrase "Should Google go nuclear?" Unfortunately he died before funding could be obtained. That doesn't mean the Polywell died with him. They're still working on it slowly, under a similar contract. They're working on new design methods and ways of obtaining fusion. Currently they're in Stage 2 of the projected R&D plan. They've validated their proof of concept, and are now working on scaling up the reactor design to get Net Power from the device. Stage 3 will be the actual construction and testing of a fusion power generation device.
Like I said, the main problem with Fusion for power generation is that a power generator must produce more than what's put in. Technically that doesn't really happen, since the first law of thermodynamics prevents it. You can only get out what is put in. The reason why fossil fuels are so effective is because energy has been stored in that crap (and yes, it is) over millions of years. Need I use the battery analogy again?
I'll explain the physics behind the requirements for Fusion. There's some high school level math involved here, so be wary. In a nuclear reaction (any reaction), the reaction energy, Q, is given by:
This is the amount of energy you'd get from a reaction. c is the speed of light, Mr is the total mass of reactants, Mp is the total mass of products. For a fusion reaction to occur, the total energy of the particles must be greater than the electrostatic force between the reacting atoms. Remember in high school, when you tried to push the north poles of two magnets together and they pushed apart. It's the same thing with two atoms. The positively chaged atoms push eachother away. The potential energy of this repulsive force is given by Coulomb's Law:
q is the product of the charge on each of the reactants, k is Coulomb's Constant (look it up), and D is the closest distance between the two particles before fusion (the sum of their atomic radii). For a fusion reaction to occur, U must be less than the total kinetic energy of the reactant particles. If your approach is heating, then this kinetic energy, E, is given by
k' is the Boltzmann's Constant, T is the temperature of the fuel. If you say U
Like I said, it's really hard to get to those temperatures. If you wanted to fuse Boron and Hydrogen, you'd need a MINIMUM temperature of 14 billion degrees! That's at normal Earth pressure.
I should note that the objective of Fusion research is mainly to achieve what is called Thermonuclear Ignition. This occurs when the fusion process reaches a state where the reactions generate sufficient energy to sustain fusion reactions without any further energy input. In a sense, what we are trying to do is literally create a second sun and contain it in a magnetic field. Think of it like a fireplace. All you need is a match, kindling, and a sturdy, heat-resistant fireplace to keep your house warm on a cold winter's night. We've got plenty of kindling, and some appropriate fireplaces, but like so many instances of birthdays at my house, we can't find the match. It's much the same case as aeons ago, when we were first experimenting with fire, trying to achieve ignition. Execpt instead of bark and sticks, we have isotopes of Hydrogen and powerful magnetic confinement vessels.
And if one would be worried about an accident at such a power station spewing out hot plasma and burning everything, be aware that the reaction is not like Fission. Fission reactions, like I said, are difficult to keep under control, and when they spiral out of control, they produce the radioactive waste and radiation we're all afraid of. The fission reaction requires an abundance of stray neutrons to occur, which can be achieved easily. Fusion on the other hand requires an incredibly?fine balance of temperature, pressure, magnetic confinement, and fuel supply. If any one of these is thrown out of wack, the process stops. In case of an accident like reaction vessel rupture, plasma may be leaked, but that's not something that hasn't already happened in scientific experiments before. Already, there are documents and studies on the safety precautions that are needed for a Fusion Reactor. Don't be afraid to live near a Fusion Reactor. They're no more dangerous than Coal Furnaces, but a lot cleaner.
There are other ways of achieving Ignition besides the brute force method of heating. One process is to have a pellet of Deuterium and Tritium, and blast it from all directions with a powerful UV laser. The energy imparted to the pellet will cause the outer layers to fuse, producing heat and pressure that would compress the inner layers to critical mass, like what happens to Uranium in a nuclear bomb, but far more controlled. The critical mass would then fuse as well, producing sufficient energy to result in a sustained reaction. Then all that would be necessary is to appropriately confine the plasma and add more fuel to the reaction. There is one test facility that recently finished contruction, called the NIF (National Ignition Facility) in California. It works on the exact same principle as I have described, and is much smaller than ITER. This also looks more promising.
One idea I recently came upon in my own research is the use of Tunneling to achieve Fusion. Remember how I said that there was a repulsion between positively charged atoms that needed to be overcome before fusion could occur? Think of this energy as a wall that needs to be scaled. It usually takes a lot of energy to climb over a wall, even for the strongest, most limbre person. An easier way would be to simply drill through the wall, wouldn't you think? This is possible in Quantum Mechanics. I'm not entirely sure of the physics, but it has been known that particles, such as Hydrogen atoms, can tunnel their way through energy barriers, like the repulsion between it and another atom. The probability of such tunneling is dependant on energy factors and such. What if there were a way to actively influence that probability, to promote tunneling? If you could generate conditions that promote tunneling, without needing to raise the temperature, then you could perhaps generate enough fusion reactions to result in Ignition. You wouldn't need to artificially generate huge temperatures or pressures, or use fancy lasers at all! You'd essentially have Cold Fusion! Well, not necessarily Cold. You could do it at room temperature, I mean.
I did some googling of my own to see if anyone had considered Tunneling as a method of Cold Fusion Ignition, but I found only one paper, and it didn't seem terribly relevant. That must mean that no one has ever properly considered Tunneling. This may be for one of two reasons: it simply didn't occur to anyone that it might work, or someone has considered it and determined there are no conditions under which Tunneling could be promoted, since it seems to be a completely random process. But come on! The simple reaction that is used to make plastic occurs randomly. It's made to produce the stuff with the desired properties by altering the conditions. Why can't we do the same with Tunneling in a plasma?
We need to start looking into less sophisticated approaches to Fusion. ITER seems to me like worthless overkill, like the LHC (did I mention that I think the LHC is worthless?). Bussard's work on the Polywell, continued by the EMC2 Foundation, seems very promising for a Hot Fusion solution, as is the NIF Reactor in California. We've already seen the mathematics required to calculate the temperatures needed to cause Fusion, and they are BIG, and while they are attainable, it demands a lot of energy input. Not only that, but in ITER, the required magnetic fields to contain the reaction are enormous, which is more energy expenditure. We need to start looking at other known phenomena, like Tunneling, to see their feasibility for Fusion Ignition. Like I said, all we need is Ignition, and we'd have a nice new green energy source.