Comment by tiberius_p
3 days ago
It still eludes me how we are going to be able to reproduce the same temperature and pressure as in the core of a star considering the humongous amount of mass (hence energy) required to create those conditions.
3 days ago
It still eludes me how we are going to be able to reproduce the same temperature and pressure as in the core of a star considering the humongous amount of mass (hence energy) required to create those conditions.
There are tantalizing ways to create fusion which don’t require these precise conditions. For example, a simple farnsworth fusor device gets fusion reactions just by causing atoms to cross paths at super high speed until they collide - they simply don’t collide often enough to release anywhere near a net energy gain.
Inertial confinement fusion, such as the National ignition facility, does generate comparable pressures and temperatures to the core of the sun within the fuel pellet for an extremely small moment during an implosion. This is done by focusing a lot of energy on small target.
Plasma confinement techniques don’t utilize high pressure to create fusion; they rely on extreme temperatures which are significantly hotter than the core of the sun, which can produce fusion events in a plasma which is only pressurized to around 1 atmosphere (they also rely on different fuel types than the sun which fuse much more readily). The key is once again focus, a large amount of energy is put into a small amount of gas. The obvious issue with this is that the extreme temperatures would destroy any physical container rapidly - but given the electromagnetic nature of plasma, it can be contained using a strong magnetic field without reaching the surface of its physical container.
While temperature may be in the stellar ballpark, pressure should be much lower. That is fine because we are not trying to do proton-proton fusion (that one is very slow even in a star) but a much easier deuterium-tritium fusion.
So, deuterium needs to be obtained from sea water through distillation and electrolysis - both energy intensive operations. And tritium comes from nuclear reactors.
I have always wondered - assuming that the confinement problem is solved, how does the cost of the fuel compare to fission (or other generation methods?
The energy cost to extract deuterium from seawater is about 1/238000th (0.00004%) the energy released from fusing that deuterium.
Nuclear fusion breeds its own tritium from lithium.
Running a 1 GW thermal fusion reactor for a year would consume $483,000 of deuterium and $1300 of lithium. At 40% conversion efficiency and 5 cents per kwh, the fusion reactor would produce $175 million of electricity in that same year.
For comparison, fuel is about 5% of the cost of electricity from fission, and about 50% the cost from coal.
The energy needed to separate deuterium is many orders of magnitude less than the energy liberated by fusion of the deuterium.
The fuel cost is small compared to fission, but note that even with fission fuel is a small fraction of the total cost, so this doesn't save much.
Basically, electromagnetic force is much stronger than the sun's gravitational force. (But it's also more difficult to get it to eork just right)
Controlled fusion does not require the conditions of the interior of a star, because the nuclear fuels involved are many orders of magnitude more reactive. All the Sun's initial deuterium (and all the lithium in the core) were burned away long ago.
Consider this - you are able to overpower the force of gravity on earth. The earth is very large, but you are stronger than it's gravity.
Gravity is so much less powerful than the other forces.