Introduction

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 Their information is out of date.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 toroidal magnetic bottles 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 that we have to try.

The situation can be compared — or contrasted — with that of the Apollo program to put a man on the moon. In that program, the physics was already known: Newton’s laws of motion covered all the physics that was needed. In the case of fusion, it took over 50 years to establish the science of plasma physics, to develop fast computers, and to understand the physics of magnetic confinement; but we have done it. In the Apollo case, there were engineering problems whose solutions could not be fully tested. Could the nose cone material stand up to the heat of reentry? Can humans survive long periods without gravity and then the stress of reentry? Will micromete­orites puncture the space suits of the astronauts? It was a dangerous experiment, but President Kennedy pushed ahead, and it succeeded marvelously. In the case of fusion, we do not know yet how to build each part of a reactor, but the only way to get this ideal source of energy is to push on ahead. The expense will be comparable to Apollo’s, but at least no human lives are endangered.

The path to a commercial fusion reactor has been studied intensely in the past decade. There are three or four steps: (1) the ITER experiment now being built, (2) one or more large machines for solving engineering problems, (3) DEMO, a proto­type reactor built to run like a real reactor but not producing full power, and (4) FPP, fusion power plant, a full-size reactor built and operated by the utilities industry.

‘Numbers in superscripts indicate Notes and square brackets [] indicate References at the end of this chapter.

F. F. Chen, An Indispensable Truth: How Fusion Power Can Save the Planet,

DOI 10.1007/978-1-4419-7820-2_9, © Springer Science+Business Media, LLC 2011

Step 2 is being hotly debated. Some think that experiments on ITER will give enough information to design DEMO. Others propose intermediate machines designed to solve specific problems such as the tokamak wall material or the breed­ing of tritium. These problems are described in the main part of this chapter. The time it will take to reach the FPP stage might look something like this (Fig. 9.1). Any additional machines for engineering testing before designing DEMO are shown in Fig. 9.1, although they may not be necessary. Although this timeline is called the “fast track” to fusion, it still will take until 2050 before fusion power becomes a reality. The economic downturn at the turn of this decade has already delayed the construction of ITER. Shortening this timeline can be done only with greatly increased funding. In the meantime, expansion of the other renewable energy sources listed in Chap. 3 is still necessary.

The two toughest engineering problems are the material of the “first wall” and the breeding of tritium. These will be discussed in detail. We also mentioned some physics problems that are not completely solved. One concerns “disruptions” which kill the plasma and must be avoided in a reactor. The best known way to avoid them is to operate safely below the tokamak’s limits, and this means less output power. Otherwise, injection of a large puff of gas can stop an incipient disruption; this is a crude solution. A second problem concerns the edge-localized modes (ELMs), instabilities that dump plasma energy into places not designed to absorb it. Currently, internal correction coils are to be inserted inside the plasma chamber to suppress ELMs as well as resistive wall modes (RWMs). This is another crude solu­tion which would not be suitable in a reactor. A third problem concerns the alpha particles (the helium nuclei) which are the products of the D-T fusion reaction. These fast ions can, in theory, excite Alfven waves, and these electromagnetic waves could disrupt plasma confinement. This instability cannot be studied until we can ignite a plasma to produce these alpha particles.

Although these seem to be formidable problems, there will be a learning curve when ITER and DEMO are built. Once industry gets serious about fusion, progress will be rapid. We will go from Model-T Fords to Mercedes-Benzes. We will go from

DC-3s to Airbus A380s. We may even get lucky with more help from Mother Nature and find that fast alpha particles are stabilizing. Where there’s a will, there’s a way. With a positive attitude, the fusion community can continue to achieve and live up to its track record of the last 50 years. Further in the future, in the second half of this century, a second generation of fusion reactors will look quite different from the tokamak as described here. There are other magnetic configurations, simpler than the tokamak, that have not been fully developed for lack of funding. These are described in Chap. 10. Better yet, there are fuel cycles that do not require tritium, thus avoiding almost all of the fuel breeding and radioactivity problems of the first generation of fusion reactors. These advanced fuel cycles can run only with hotter and denser plasmas than we can now produce, but which may be possible once we have learned how to control plasma better. Advanced fuels are also presented in Chap. 10. The engineering problems described here are not the end of the story.