The Future of Fusion Energy

Jason Parisi, Justin Ball

• Publisher: WSPC (EUROPE)
• Year: 2018
• ISBN:
  9781786345448
• Topic: Sciences physiques
• Subtopic: Physique

The gap between the state of fusion energy research and public understanding is vast. In an entertaining and engaging narrative, this popular science book gives readers the basic tools to understand how fusion works, its potential, and contemporary research problems.

Written by two young researchers in the field, The Future of Fusion Energy explains how physical laws and the Earth's energy resources motivate the current fusion program — a program that is approaching a critical point. The world's largest science project and biggest ever fusion reactor, ITER, is nearing completion. Its success could trigger a worldwide race to build a power plant, but failure could delay fusion by decades. To these ends, this book details how ITER's results could be used to design an economically competitive power plant as well as some of the many alternative fusion concepts.

Contents:

• Motivation:
  • The Hydrogen-Powered Civilization
  • Energy in Numbers and Graphs
• The Basics:
  • Fundamentals of Fusion Energy
  • Plasma Confinement
  • Fusion Technology
• The State of the Art:
  • The Past: Fusion Breakthroughs
  • The Present: ITER
  • The Future: Designing a Tokamak Power Plant
• Special Topics:
  • Alternative Approaches to Fusion Energy
  • Fusion and Nuclear Proliferation
  • Fusion and Space Exploration
• Conclusions:
  • When Will We Have Fusion?

Readership: Motivated laypeople with an interest in fusion.Fusion;Fusion Energy;Nuclear Fusion;Physics;Popular Science0 Key Features:

• There is no book on fusion that is this accessible to the motivated layperson

PART 1

MOTIVATION

Chapter 1

The Hydrogen-Powered Civilization

Life needs energy. It always has and it always will. From the simplest bacteria to the most complex civilizations, we need energy to survive.

In this book, we’ll take a look at the dominant source of energy in the universe — fusion. By smashing hydrogen atoms together to form helium, we can release fusion energy and ensure a sustainable future for ourselves and our planet. However, before we delve into fusion exclusively, the first two chapters will discuss the wide variety of energy sources available to us and fusion’s place among them.

1.1Revolutions in Energy Use

Energy is the basis of modern civilization. The ability to power the objects that enrich our lives is a hallmark of society. Moreover, without the ability to power machines to do useful work, the current world population could not be supported. But how did we get to this point?

Humanity’s desire to capture and control external flows of energy predates humanity itself. This is because it wasn’t humans, but rather early hominids who first harnessed fire. Though intuitively obvious, fire has three enormous advantages. First, it could be used by the proto-humans to stay warm, thereby reducing the number of calories they needed to consume. Instead of going to the trouble of finding extra food to eat, they could gather nearby vegetation and light it on fire. Second, fire opened an enormous reserve of energy that was previously inaccessible: inedible but flammable material. Finally, it could be used for cooking and light, both tasks that no amount of manual human labor could accomplish. This was the first step in a series of discoveries that unlocked previously inaccessible energy and enabled it to be used in profound ways.

The first agriculturalists used their own bodies to plough fields, dragging the heavy apparatus through the soil. This, however, was a lot of work (according to both the physics and conventional definitions¹), so humans found animals to do it instead. Oxen and horses, with far more powerful and durable bodies, ploughed our fields and transported people around. Up until the 18th century, animals remained a primary source of power enabling human survival. These beasts of burden were organic machines powered by raw grasses, which human stomachs have difficulty digesting. Though this was a fairly inefficient process, it accessed a new energy source and, since human populations were so low, efficiency wasn’t particularly important. Energy abounded, we just needed to find more ways of harnessing it.

In these early times, there were just a few examples of energy manipulation that did not involve living things. Windmills and waterwheels captured the flows of wind and water to process grains and irrigate fields, while the sails of ships enhanced human transportation and exploration. Still, for the most part, we relied on animals and burning plants to enable human survival. This reliance on animals began to change substantially with the invention of the steam engine. The steam engine has a rich and complex history, but here it suffices to say that it became commercially available in the early 18th century. The steam engine was the first device capable of transforming the heat energy from fire into useful mechanical work (see Figure 1.1). While it was initially limited to pumping water out of coal mines, it would eventually power the Industrial Revolution.

Figure 1.1:A four-frame cartoon of a very early steam engine, which converts heat energy into the motion of a piston. First, water is boiled using the heat, which creates steam that pushes the piston upwards. Next, a valve is opened, letting a small amount of cool water into the chamber to condense the steam. Thus, the piston falls downwards under the weight of gravity. Finally, a valve is opened releasing steam back into the chamber and the cycle is repeated.

Though steam engines were extremely useful, they were only able to do mechanical work.² However, in the early 19th century, the British scientist Michael Faraday was to create a new energy paradigm, that of electricity. Faraday discovered electromagnetic induction — the fact that an electric current is induced when a conducting material is moved through a magnetic field. Electromagnetic induction was a revolutionary idea that we’ll come across again and again in this book. By moving a metal wire past magnets, you can convert mechanical energy into electricity. This works because electricity is carried by the flow of electrons. Since electrons have an electric charge and are very light, the magnetic field strongly affects them and can easily induce them to move. Electromagnetic induction generators became so important because electricity is easy to transport long distances and can be efficiently converted into other forms of energy. This versatility allowed energy generation to be decoupled from energy consumption, enabling both power plants and appliances to plug-and-play into an electrical grid.

Following electromagnetic induction, humans discovered a number of other ways to generate electricity. For example, the photovoltaic effect directly converts light to electricity, enabling photovoltaic solar panels,³ and the Seebeck effect directly drives electricity from temperature differences (i.e. thermal energy). Nevertheless, to this day, the vast majority of electricity is still generated by moving a conducting material through a magnetic field.⁴

Many inventors, such as Thomas Edison, realized the usefulness of electrons moving along a wire. Edison’s most celebrated product, the incandescent light bulb, uses these electrons in a very clever way.⁵ By directing electrons through a resistive carbon filament, they are forced to slow down, thereby transferring the energy to make the filament heat up. Once the wire is sufficiently hot, it radiates visible light! While modern appliances use electrons in far more ingenious and varied ways, the way they are powered remains unchanged — by electromagnetic induction forcing electrons to move along metal wires.

Induction allowed mechanical energy to be converted into electrical energy, enabling the widespread use of electricity. In practice, this is accomplished by rotating a giant, conducting metal disk called a rotor, through the magnetic field generated by magnets. However, how does one get the mechanical energy to rotate the rotor in the first place? For the most part, power plants still use an advanced form of the centuries-old steam engine: the steam turbine.⁶ Most energy sources people are familiar with (e.g. coal, oil, gas, nuclear, biomass, and geothermal) are just different methods to create steam. The moving steam transfers energy to the generator rotor, which rotates and induces the electric current. All of this to power your toaster (see Figure 1.2).

Figure 1.2:How we use the Earth’s energy resources to make toast.

1.2Comparing Options

Selecting what combination of energy sources to use to generate electricity is immensely complex. For a start, the energy reserves of the different sources, as well as their rate of replenishment, vary dramatically. Fossil fuel reserves can only last for a few hundred years and get replenished exceedingly slowly. In contrast, the Earth’s solar resources will be continually replenished for the remaining five billion year lifetime of the Sun (at least when it’s not cloudy). The amount of fusion fuel is not replenished, but it is so immense that it has the potential to power our civilization for billions of years. Another consideration, the energy density of a source, also varies enormously. To satisfy the current electricity consumption of all Americans using nuclear fission (i.e. the usual nuclear power you hear about) would only take hundreds of square miles (the size of a typical city). Solar, on the other hand, would require tens of thousands of square miles (roughly half the size of West Virginia), while wind would need much more (roughly the size of California).⁷ However, while these considerations are important, the things we fundamentally care about (things like sustainability, environmental impact, and obtrusiveness) are not so straightforward to quantify.

In order to simplify our decision-making process, we generally let the market decide, assuming that the cost of electricity accurately accounts for the myriad of competing considerations. However, while the market is effective at minimizing costs in the short term, it tends to ignore time-scales longer than the tenure of CEOs. Furthermore, negative externalities (i.e. costs imposed on people who are external to the transaction) abound in energy production. This means that the cheapest source for the individual consumer isn’t necessarily the cheapest for society. The most prominent example of this is the emission of carbon dioxide into the atmosphere by burning fossil fuels. When someone buys electricity generated from coal, it imparts a cost, not just on themselves, but on all of society. In emitting greenhouse gases, we are taking out a loan, a loan that must be repaid many times over by future generations. Our descendants will be forced to contend with a changing and less habitable planet. Another externality concerns nuclear fission power, which can aide in the construction of nuclear weapons. As a result of fission generation, governments must use our tax dollars to ensure that nuclear fuel and nuclear waste do not fall into the wrong hands. Moreover, nuclear weapons are just a small example from the much broader costs of conflict. Relying on scarce, concentrated energy resources can drive conflicts (e.g. oil wars in the Middle East) that have enormous financial and human costs. And these direct costs may very well be small compared to the effect that war has on international trade and global development.

Regardless, the world is hungry for energy. The Intergovernmental Panel on Climate Change estimates in their baseline scenarios that energy demand will increase by a factor of three by 2100 (and electricity demand will increase from 20% of energy consumption to 50%) [1]. In developed countries, we tend to think of this as a bad thing. To us, it implies that more energy is being wasted or used for superfluous purposes. But across the world, an increase in energy consumption reflects a positive trend — that the global standard of living is rising. Even if developed countries can moderate their energy consumption, the developing world deserves the additional energy needed for health, education, transportation, nutrition, leisure, etc.

In light of all the above, it is clear that we must be deliberate in deciding what energy sources to pursue. It is complex and consequential. We should think deeply and carefully to come to well-informed conclusions. Then, through collective and individual action (e.g. voting, consumer spending, career choice, etc.), we should endeavor to make our desired energy development plan a reality. In the next chapter, we will provide a systematic introduction to the Earth’s energy resources. This will serve to guide our thinking on energy policy as well as motivate our investigations into fusion.

¹Work is defined by physicists as the amount of energy used in a process (i.e. the force times the distance over which it is applied).

²Mechanical work is restricted to moving a macroscopic object, such as a piston. The modern combustion engine in your car mainly does mechanical work, since it serves to rotate the wheels. Similarly, a jet engine does mechanical work by pushing a plane through air.

³When the photons in light strike a material with sufficient energy, they can excite the electrons in the material, driving an electric current.

⁴Strictly speaking, about 1% of all US electricity generation does not rely on electromagnetic induction, namely photovoltaic solar panels.

⁵Edison was not the creator of the light bulb, but he was the first to commercially produce it.

⁶Wind turbines, tidal power, and hydropower are exceptions to this as the movement of the wind/water directly causes the disc to rotate.

⁷Though there is space to do things amongst wind turbines.

Chapter 2

Energy in Numbers and Graphs

Now that we have outlined humanity’s history of energy consumption, we’ll let the numbers do the heavy lifting as we undertake a systematic review of the dominant energy sources available on the surface of the Earth.¹ But first, what does it mean to “consume” energy? After all, you may have heard that energy is conserved, so where does the energy go? And will energy in the universe ever “run out”?

2.1Can We Even Consume Energy?

The answer is that energy is never consumed — it is simply converted to other types. However, it can make sense to talk about “consuming” energy (as we will) because not all types of energy are equal. For example, when we heat water in an electric kettle, we are converting electrical energy into heat energy. While we could have used the input electricity for any number of tasks (e.g. powering lights, speakers, clocks, toasters, etc.), the resulting heat isn’t so versatile.² Operating a kettle does not destroy any energy, but it does cause some energy to become less useful.

The principles underlying the usefulness of energy are quite technical and stem from the entropy of different energy types. Entropy is a rigorous way of quantifying the amount of order in a system — the more disordered the system, the higher the entropy. Physics tells us that the entropy of an isolated system will increase with time. In other words, things tend to chaos. Types of energy with low entropy (like electricity) are more useful because we can take advantage of their order to do things that we want. The directed march of electrons down a wire can be manipulated much more purposefully than the haphazard and random motion of a hot gas. Again, this isn’t to say that heat energy is always completely useless, just that it is less useful per unit of energy. This is seen most clearly from air conditioners used to cool homes. Air conditioners can use one unit of electrical energy to move four units of heat energy from inside your house to outside. This contrasts with st...