Thread: Energy Awareness?

Since we're on the subject of greener alternatives and cutting emissions, etc, an often overlooked aspect is the way we fight our wars. How can we wage a more eco-friendly war?
Here's an informative video on the topic.

http://www.youtube.com/watch?v=Mvz_xzaMvCQ

http://news.yahoo.com/s/ap/20080322/.../military_coal

Originally Posted by HBrutusH

[science] Couldn't they just crack the petrolium polymers into shorter monomers to increase the amount of fuel they gain from it? Or would that just mean that cars would burn more fuel to achieve the same affect?[/science]

You can't beat thermodynamics. You aren't getting any extra energy by breaking it down so you are going to make a net loss in the process. This is doubly so since shorter hydrocarbons can't be converted to energy as efficiently as longer hydrocarbons (lower Carnot efficiency since they have lower flash points).

Actually, on the subject of fusion: I saw a tv program which showed a prototype fusion reactor (being developed in some Mid-England university) which actually works. The only problem is that it uses more power to start the fusion prossess (re:big magnets) than it actually gains from it. Still, might not be long until we get fusion powered space ships, at least.

Actually, making corpses into oil isn't such a bad idea.

here's a pretty (and real) picture of a fusion reactor. the cut out view is through an infra red lense while the reactor is running. (for the few seconds it can before it fuses)

That's a tokamak reactor; the problem with the tokamak is it was really the first design that 'could' work, by which I mean it wasn't obviously flawed to the point where it could be dismissed without even construction of a prototype. Yet somehow the realm of high-energy plasma fusion has remained obsessed with this single, original design, and it has soaked up almost all the research dollars available for the past 30 years. To paraphrase some physicist... we've spent billions of dollars and 30 years researching tokamaks and all we've learned is they don't work. The design originally came from a soviet physicist and some have jokingly suggested that the Russians giving it to the west was actually industrial sabotage. The universe is full of fusion reactors and none of them look like the tokamak.

The design that excites me is the Polywell reactor, which is the reactor the US military has been quietly funding research into for the past decade.

Originally Posted by HBrutusH

Resource link for the Polywell?

How is the other design flawed? From what I've read it just puts immnense amounts of magnetic pressure on hydrogen (?) in an atmosphere of boron(?) and smushes them together.

Explain please

I really like the idea of fusion, the power that could be made is immense, with no radiation (besides heat+ light?) or harmful waste.

Well, there are two parts to the tokamak problem.

The first is simple engineering. A power generating tokamak is basically a big torus (donut) with three layers. The inside is the core, which is emptied to a vacuum and contains the plasma that should (in theory) be reacting. The core then sits immersed in molten lithium deuteride (which is kept at around 1000K). Then outside that are your superconducting magnets, which need to be kept at around 5K. The first problem is your have your supercooled magnets at 5K sitting next to molten lithium deuteride at 1000K, so it's a challenge to keep everything at the right temperature, and a lot of energy. The second problem is that the lithium deuteride and its containment can't interact with the magnetic field. The third is that molten lithium deiterode is quite reactive and likes to explode when exposed to air, and it produces highly toxic fumes when it burns.

Now you need LiD for two reasons. The first is that tokamaks use what's called a Deuterium-Tritium reaction; tokamaks react deuterium and tritium (two isotopes of hydrogen), and when they fuse they make Helium-4 and a fast neutron. Deuterium is common enough (it can be extracted from sea water) but tritum is unstable (radioactive) so it has to be made... this is what the molten lithium deuteride is for- the neutrons generated react with the lithium deuteride to produce lithium. They also HEAT the lithium, a lot. So the lithium needs to be cycled, have the tritium extracted (which is then pumped into the reactor core) and run through a heat exchanger. The heat exchanger then drives a normal thermal power plant, which will convert the heat into electricity with about 50% efficiency. And a lot of that power has to be cycled back to the electromagnets and the cooling systems. Plus, not all the neutrons are captured by the lithium deuteride, and they will make the reactor vessel radioactive.

So that's a tremendous engineering challenge, which is largely why ITER is supposed to cost about $15 billion dollars to build.

Now for the HARDER problem, the physics of the tokamak.

You can't really squeeze a plasma with a magnetic field. Magnetism is a right-hand force, which means that it acts on particles at right-angles. An ion or an electron whizzing through a magnetic field gets spun around in a circle, it doesn't get squeezed or anything. Tokamaks use two magnetic fields to contain their plasma... the first makes the particles travel in tight spirals. The second loops the spiral around into a circle.

Now there are two main forces at work within a fusion reactor- the first is electromagnetic, which is the dominant force. The magnets use the electromagnetic force to guide the particles around the inner chamber, and the atomic nuclei in turn electrically repell each other (since they're all positively charged). The other force is the nuclear force, which is extremely strong over very short distances, but loses strength very quickly as the distance grows. Normally nuclei in the reactor don't interact at all... the magnetic containment fields dominate all other forces, but occasionally two nuclei get close enough that they interact with each other. Now as hot as the plasma is, the plasma's energy has a maxwell-boltzmann distribution, so only a tiny fraction of all the particles in the plasma have enough kinetic energy to fuse. Even when the particles interacting have enough energy, there's still only a 0.1% chance that they'll get close enough to fuse. The vast, vast, vast majority of interactions are failed interactions, and in failed interactions one of the particles tends to get kicked a little bit further out of the particle stream. It's a random process, but the tendency is for the flow of particles to slowly drift away from the center of the reactor to the walls. Magnetic containment isn't true containment; there's no restoring force to push the particles back to the center, so there are constantly particles impacting the reactor wall. This erodes the vessel wall and bleeds tremendous amounts of energy out of the reactor.

Here's the kicker... you can minimise this effect somewhat by increasing the strength of your magnetic fields, but that increases bremsstrahlung radiation. The more powerful your containment fields, the more bremsstrahlung radiation is generated by the reactor. A plasma in a tokamak will quickly bleed all its energy away through bremsstrahlung radiation.

Unlike the engineering challenges, these are basic design flaws due to the physics of the tokamak. There's a reason you don't see any donut shaped stars.

Experimental polywell reactor (outside of its vacuum chamber)


Polywell (polyhedral potential well) is an IEC (inertial electrostatic containment) reactor design. Polywell is really clever since it doesn't try to directly contain the reacting plasma. The six electromagnets are used to contain a high energy electron cloud in the center. The electron cloud is contained by the magnetic fields and energized by microwave radiation, and by fiddling with the magnetic field strength and the microwave strength it's possible to precisely control the energy distribution within the core. Then you inject low energy hydrogen and boron ions into the reactor. They're positively charged and the core is negatively charged, so they're accelerated into the centre of the reactor (the potential well) to very high energies. Since they're being accelerated by electrostatic attraction rather than by heating they accelerate to a fairly uniform energy level, so almost all your ions have potential for fusion. So there's no slow ions that are bleeding away your energy, like in a tokamak. The other cool thing is that if the particles don't fuse, they pass through the core and then stop and are pulled back in from the other side. It still might take 1000 tries before a fusion occurs, but there's almost no energy loss from failed interactions.

The really cool part is that the fusion reactions occur in the centre of the core, in the middle of the electron cloud. The reaction is a boron-proton reaction which is an unusual fusion-fission reaction (boron-11 and the proton form super-energized carbon-12, which rapidly decomposes into helium-4, releasing more energy), which produces no radiation at all. Unlike a tokamak you can actually do boron-proton in a polywell since it has precise control over the energy distribution of particles inside it. Most of the energy from the reaction is captured by the electron cloud. There's a certain amount of physics in this next step I don't understand, but from what I've been told there's a process to extract electrical current directly from the cloud, so there's no thermal energy losses. A full sized reactor is estimated to produce 2,000,000 volts of DC electricity, and about 120GW of power. Ten full sized polywells could power the entire continental USA, and since it's not a thermal plant you don't need millions of gallons of water to cool it.

It was invented by Robert Bussard, one of the pioneers of fusion research, who unfortunately died of cancer last year. :-(