The Azimuth Project
Nuclear fusion

Contents

Idea

From Wikipedia:

Nuclear fusion is the process by which two or more atomic nuclei join together, or “fuse”, to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy. Large-scale thermonuclear fusion processes, involving many nuclei fusing at once, must occur in matter at very high densities and temperatures.

The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy while the fusion of nuclei heavier than iron absorbs energy

Details

Methods

Currently, two of the most strongly funded methods of achieving fusion are magnetic confinement and laser inertial confinement.

Magnetic Confinement

Magnetic confinement usually refers to devices such as the tokamak, which is basically a toroidal chamber with corresponding magnetic fields that “hold” the plasma. The plasma is then heated externally by methods such as RF heating, neutral beam injection, etc. which are, at its base, just methods of transferring energy into the plasma, either through waves or particles.

An ideal working reactor from this scheme would be self-sustaining. That is, we will be able to start the reaction, and it will provide enough of its own energy to maintain fusion reactions. In this ideal scenario, the process is continuous as long as we feed it fuel.

Some of the more well-known projects involving magnetic confinement are ITER, DIII-D, JET, NSTX, and so on.

Laser Inertial Confinement

As the name implies, there are lasers involved with this method. In this scheme, many lasers are aimed at a single pellet of some combination of hydrogen and other fusion fuel. The idea here is to cause the pellet to implode on the surface and create a fusion reaction.

An ideal working reactor from this scheme would not be continuous. It would require shooting a fuel pellet, inducing fusion, extracting the energy, then repeating the process again.

This method is being explored at NIF.

Other Methods

In addition, there are various other non-mainstream methods such as (but not limited to):

  • Field-Reversed Configuration (FRC)
  • Magnetized Target Fusion (MTF)
  • Polywell

These schemes are currently pursued or funded by Tri-Alpha, General Fusion, and the Navy, respectively.

Questions

What are the claims of (future) fusion research?

There are three main claims for fusion, and these are that it is cheap in fuel, high in safety, and friendly on the environment.

Since fusion reactions are mostly efficiently achieved with low numbered elements, specifically various isotopes of hydrogen, the claim in that it is cheap in fuel comes from the fact that these isotopes of hydrogen can be extracted from our ocean waters. Assuming the isotope used in the fusion reaction is deuterium, it has been estimated that the extracted energy would last 150 billion years1. This is the basis of the first claim of “cheap” fuel.

The second claim of safety comes from comparison to fission processes. As we know from past instances, fission reactors have the ability to start a self-sustaining process. Both fortunately and unfortunately, fusion reactors do not have this ability because as soon as the plasma is uncontrolled and hits the wall of the reactor, the plasma will cool and the process will not be able to move on. This is why there is an inherent safety in the fusion process.

Finally, the claim of environmental friendliness comes from the resultant products of the fusion process. Ideally, in a fusion reactor, the only radioactive results are the chambers of the reactor, an indirect result of high energy neutrons (produced by the fusion reactions) damaging the walls. Hopefully, this will be mitigated by advanced research in material science, but in the event that there is still a finite half-life, it would still be much less than the radioactive results directly produced by fission reactors. In addition, fusion reactors will not spew out pollutants like fossil fuels which promptly puts above those two other energy sources in terms of environmental friendliness.

Would it be possible to speed up fusion research?

References

For more on Nuclear Fusion, see:

Recent progress in stellarator research:

  • T. Sunn Pedersen, M. Otte, S. Lazerson, P. Helander, S. Bozhenkov, C. Biedermann, T. Klinger, R. C. Wolf, H. -S. Bosch & The Wendelstein 7-X Team, Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000, Nature Communications 7, Article number: 13493 (2016) doi (open access)

Citations

category: energy


  1. Energy for the Future(PDF warning)