|Posted by Craig on September 15, 2012 at 6:55 AM||comments (0)|
Whew... Been back for three or four days now. Recovering from MASSIVE jet-lag, so haven't written up much. Don't worry. Will talk about my trip tomorrow. And upload some photos as well.
This is just to mention that I'm back.
And while recovering from said jet-lag, I spent my sleepless nights studying orbital mechanics. I understand so much more about them now, so much that I worked out how to model them in a computer. Yay for me! I plan to use this in my world building eventually, as soon as I can work out some issues with my Galaxy Generator program.
But for now, feel free to read up on my work, which I'm linking to here.
Anyway, will talk about the trip tomorrow.
|Posted by Craig on July 4, 2011 at 9:48 AM||comments (0)|
This follows on from my fusion post.
After looking at some Polywell updates, I've come to a slightly better understanding of the physics and their progress rates. Also, I've come up with some environmental impacts of widespread fusion proliferation.
The Polywell, like I said in my previous post, started with Farnsworth-Hirsch Fusors. Now, Farnsworth was in fact one of the engineers credited with the invention of Television. His fusor design is very similar in concept to the old CRT televisions.
Now, for those who can't remember the times when TV's were large and pyramid-shaped (instead of the sleek, sexy flat-screens), CRT stands for Cathode-Ray Tube. In the 1890s, a British physicist named J. J. Thompson had an idea to suck the air out of a glass tube, and stick two electrodes in there to see if empty space could conduct electricity. What he ended up discovering was something he called Cathode Rays. It turns out, these were in fact electrons he had discovered. He determined they had mass and charge. Lo! and Behold! about thirty years later, we have Television.
CRTs work like this: one of the electrodes becomes highly negatively-charged when a current is applied to the tube (as electrons build up on it), while the other electrode becomes highly positively charged (as electrons are stripped away). Eventually, the difference in charge causes the electrons at the negatively-charged electrode to jump across the gap and become attracted to the positively-charged electrode. The former is called the cathode, the latter the anode. This is high-school level physics, and it's relevant to fusion as well.
Back to Farnsworth. The guy had the idea that if CRTs accelerated electrons, could a similar technique be used to accelerate positively-charged protons. Consider this: remember the equation to calculate the kinetic energy of a particle at a certain temperature? Now, if you know the mass of a particle, you can work out its kinetic energy from simple motion. If v is the particle's velocity, and m is its mass, then its kinetic energy Ek is given by:
Okay, now suppose that the kinetic energy from heating is the same as the energy from moving (a reasonable assumption, since when dealing with tiny particles, temperature is only the macroscopic effect of their high-speed movement). Solve the resulting equation, and you get:
Say you've got a proton travelling at 1 kilometre per second. Plug the proton mass and Boltzmann Constant into the equation, and you get an equivalent temperature of around 40 Kelvins. That's not much, but the temperature will rise quadratically with velocity. Check out the chart below. You get to around room temperature with a velocity of 2.5 km/s.
In a CRT tube, the electrons can get to huge speeds, since there's no air, and the particles are extremely light. If you calculate the necessary temperatures to fuse two protons from the equations in the previous post, you'll find that the necessary velocity is a verysmall fraction of the speed of light, which is bloody easy to achieve. And Farnsworth said to himself, "Why not do the same with protons, and fuse them?"
So he built a device that has an electrical grid designed to confine plasma inside its electric field. Then there's another grid inside that one, negatively charged, which serves as a cathode attracting positively charged particles. The protons are accelerated toward the grid, meet in the centre, and fuse. It's actually pretty easy to do this, and it's a common high-school project.
The main problem with Farnsworth's fusor is that the protons collide with the grid and lose far too much energy to ever achieve break-even energy production or ignition. The Polywell seeks to solve that problem. Instead of having a cathode in the form of a negatively-charged grid, the coils generate a magnetic field that causes electrons to pool in the centre. This creates something called a virtual cathode. In other words, it's negatively charged air. The protons are attracted to the core, but don't have a grid to collide with. And when they hit the electrons, they have so much energy that the electrons bounce off them (or more like glance off). This does result in a loss of energy, due to Bremsstralung (Breaking) Radiation, which is given off by the protons as they interact with electrons. But this isn't nearly as big a loss as grid collisions.
So, now we can see that there is merit to the Polywell. But it's a little early to be optimistic. Remember I said fusors lost too much energy to grid collisions? Well, while there may be much less energy loss due to Breaking Radiation, we still need to make sure that the gains from the reactions can make up the loss. It may be that the losses are still too great to achieve break-even production. That is one of the other reasons EMC2 and the U.S. Navy are taking it slow on a shoestring budget. ITER is run by the governments of the world, primarily (I believe) as a publicity stunt. That's why they're taking such a massive step in constructing a reactor the size of the Empire State Building. The Polywell, on the other hand, is focused on smaller-level applications, like powering submarines. There's no interest in publicity. Moreover, expending so much money on a concept that might not be fully developed (like the US$200M required for a test Polywell reactor) could end up being a waste. So they're taking their time. EMC2 is cautiously optimistic that it will work, stating "There's no reason why it shouldn't." Having just completed a finance subject, I can understand and appreciate that position. Even though I don't really have an advanced degree in Physics, or even do too well in the subject in my undergraduate, I do feel confident that the Polywell will work. All it'll take is time and money.
Having said that, one thing I seriously hope the proponents of fusion (and other green tech) are considering is environmental impacts. Just because it's green or has no carbon footprint, it doesn't mean it won't have some other impact that's just as serious as Global Warming (and all the GW naysayers reading this, you're idiots). I actually conceived of this idea while running a thought experiment of the industrial process of a Polywell Reactor's operation. Let's recap: You have your fusion fuel, Hydrogen. The reactor takes this, and pumps out Helium. It actually uses the product to generate electricity in a highly efficient manner. It's also very safe, in that if the reaction chamber is breached, the worst that could happen is a fire from the plasma (and it's not like that hasn't happened in the past anyway). There's no risk of fallout either. The Helium products can then be shipped away to be used in MRI machines, blimps, and kids' birthday parties. Here is where I detect an environmental drawback. It lies in the current wasteful usage of Helium. Since the element is so cheep and abundant - an abundance made even greater by the use of fusion reactors - society uses it frivolously. We breathe it in to make our voices funny, we give balloons full of it to kids who almost immediately let it fly into the sky, we might even accidentally let it leak out of a tank somewhere. Due to its non-toxicity, it is released into the atmosphere with little thought. It has no environmental impacts, and does not interfere with Ozone, like CFCs do. But when it reaches the atmosphere, it escapes into space and cannot be recovered.
Can you see the point I'm trying to make? We take Hydrogen from water, Boron from the earth, fuse it into Helium, and then let it waft away into space, never to be seen again. By this process, the Earth would quite literally evaporate. By not treating Helium carefully or finding a way to convert it into other useful compounds like carbon or oxygen (by further fusion reactions - that's possible), we will in fact do more harm to the planet than Fossil Fuels ever could.
I'm not saying that we should give up on this. Don't misunderstand me. The point I am trying to make is that we must anticipate these problems now and build not only infrastructure to solve them, but the correct attitudes as well. The problem we have with Fossil Fuels now is because we reached a point where we can't live without them, and only then did our science realise the negative impacts it was having on our planet. We are now in a very unique position to make a change. But we have to do everything in our power to make sure we handle these issues in the correct way. The way to counteract the Evaporating Earth Hypothesis - if it turns out to be correct - is to simply continue the fusion reactions further until we get other useful compounds out of it, like Lithium and Carbon.
There. I presented a problem and the solution, thereby circumventing the mistake made when the Industrial Revolution started. We need to challenge our imaginations to find all the possible problems and impacts associated with emerging technologies, and develop simple solutions. Then, we can enact the fruits of our labour, and get on track to a cleaner human society.
|Posted by Craig on April 17, 2011 at 7:28 PM||comments (8)|
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.