Fusion Progress
So let's look at the physics and engineering behind making fusion a viable energy source and see where we actually are! Francis Chen wrote a book titled, "An Indispensable Truth: How Fusion Power Can Save the Planet." Chen starts his book with a reference to Al Gore's book about climate change, "An Inconvenient Truth" and it seems more than coincidental that his title is so reminiscent! Chen highlights the tremendous challenges faced and overcome in developing plasma physics, many of which were unforeseen. However, he believes fervently that the majority of the physics is established at this point and many of the issues, albeit substantial, are engineering concerns. Chen acknowledges that "Fusion has suffered from the reputation that it is always promised to be available in 25 years. This was because the difficulties were not initially known. They have been overcome, but it took time and funding to build the necessarily large research machines, to train a generation of plasma physicists, and to develop the diagnostic tools to be able to see what we are doing. The underlying physics is now understood well enough that more accurate estimates of what it takes to make magnetic fusion work can be made. Thousands of dedicated physicists and engineers labored for decades to bring fusion within the foreseeable future. There are still a few physics problems to be solved. Engineering is another matter. What has to be done to make fusion reactors practical is the subject of [chapter 9]."(11) He goes on to indicate that "With the information they have gathered from the public media, most people who have heard of fusion consider fusion energy to be a pipedream. Their information is out of date. As we have shown in the last two chapters, great advances have been made in fusion physics, and our knowledge of plasma behavior in a toroidal magnetic bottle is good enough for us to push on to the next step. This does not mean, however, that fusion is not a pipedream. There is a large chasm between the understanding of the physics and the engineering of a working reactor. There are problems in the technology of fusion so serious that we do not know if they can be solved. But the payoff is so great we have to try."(12) So in the end, Chen does not end up that far from Seife except that he is more knowledgeable and specific and he makes a far more compelling case.
For fusion to occur and a net energy output, meaning more energy is produced than goes in to creating the reaction, the conditions must be just right. John Lawson first showed these criteria. The three primary factors, called the triple point, that must be considered are temperature, T i, of the ions, n, the density of the ions or the electrons and time of interaction, Τ E (tau), the energy confinement time. These factors must be multiplied to produce a sufficient product for fusion to occur. According to Chen, this measure of success has increased over 100,000 times in the last forty years and doubling every two years recently.(13) This certainly bodes well for the future progress that fusion research and development of a reactor is likely to make. These parameters allow for the nuclei to overcome the coulomb repulsion and predominantly the potential energy associated with the strong nuclear force. It also turns out that quantum tunneling is necessary for the reaction to occur. The nuclei must be accelerated to 100,000 Volts. But none of this is possible unless the potential energy of the triple point is achieved so that the required potential energy for the reaction to occur can be achieved.Magnetic Confinement Fusion
The most prevalent current method for creating the conditions for fusion is called magnetic confinement fusion. The majority of the work over the past fifty years has been on Magnetic Confinement Fusion (MCF). One of the most challenging problems about creating a controlled fusion reaction is that the fusion material must attain at least 100 million degrees! Consequently, the fusion reaction must occur without touching any boundary materials because they would melt. So, the ingenious way that this has been solved is to suspend the fusion material in a field. At such extreme temperatures, atoms dissociate, or ionize, from their constituent parts and become a plasma. A plasma is the fourth state of matter, besides the familiar solids, liquids and gases, and it exists when atoms are stripped apart. The protons and their electrons are separated. The fusion material before it is heated is neutral, meaning that it has the same number of protons and electrons. Therefore, after being heated, the plasma, as a result of the conservation of charge, must still have the same number of positive and negative charges and still be neutral. This is very important in the ability to create magnetic confinement.
Magnetic confinement works because a magnetic field interacts with an electric field and vice versa. So, it is conceivable to create a strong enough magnetic field to contain the plasma, which is made up of charged particles. Natural magnets by themselves are not strong enough to contain 100 million degree plasma; however, electromagnets are strong enough if supplied with enough current. There are a couple of challenging aspects to contain a plasma, however. The first is that the electromagnetic fields do not act parallel to each other but instead act perpendicular to one another by the formula F=q(vxB) by the "right-hand rule." What this means is that the charged particle with charge q which must be in motion with velocity v, experiences a force (F) perpendicular to the magnetic field(B), in a right-hand orientation for a positively charged particle. Since the particles of the plasma must be in motion, the only way to contain them is to have them go in a circle. The shape of the "doughnut" is called a torus. But it gets even more fun, because the forces on the oppositely charged particles experience opposite directions. The ingenious solution is to twist the torus shape into a slight helix, so the resultant form of the predominant magnetic confinement vessel is known as a helical toroidal tokamak.
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