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- Herausgeber: Icon Books
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
'Holgate guides us expertly and with a deft touch along the journey towards the holy grail of unlimited energy for all.' - JIM AL-KHALILI 'What is nuclear fusion? In clear and accessible language, this book explains the basics and the hope for the future. A valuable addition to the Hot Science series.' - JOHN GRIBBIN Could the Sun hold the key to a future of clean energy? Since the 1950s, scientists have attempted to harness nuclear fusion - the process that creates the Sun's energy - to generate near-limitless amounts of electricity. But the fact that we still have no fusion power plants is testament to the complexities of the challenge. Now, the deepening climate crisis means that researchers around the world are in a race to create a mini-Sun here on Earth. The glittering prize is an energy source that emits no greenhouse gases and could solve energy equity and supply issues at a stroke. Sharon Ann Holgate, a former Young Professional Physicist of the Year, tells the compelling story of the ongoing scientific quest for a revolutionary new era of green energy production.
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Veröffentlichungsjahr: 2022
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vFor Micah, in the hope that his generation will benefit from fusion power
ABOUT THE AUTHOR
Sharon Ann Holgate is a freelance science writer and broadcaster with a doctorate in physics. She has written for newspapers and magazines, including Science, New Scientist and The Times Higher Education Supplement, and has presented on BBC Radio 4 and the BBC World Service. She was co-author of The Way Science Works (Dorling Kindersley, 2002), a children’s popular science book shortlisted for the 2003 Junior Prize in the Aventis Prizes for Science Books, and recently completed the second edition of her undergraduate textbook Understanding Solid State Physics (CRC Press, 2021). She has also written the Outside the Research Lab textbook series (IOP Publishing in conjunction with Morgan & Claypool Publishers) and contributed to the popular science books 30-Second Quantum Theory (Icon, 2014) and 30-Second Energy (Ivy Press, 2018). In 2006, Sharon Ann won Young Professional Physicist of the Year for her work communicating physics. You can follow Sharon Ann on Instagram @everydaysciencethings
www.sharonannholgate.com
ACKNOWLEDGEMENTS
My thanks go firstly to series editor Brian Clegg, who I rather fittingly first discussed the possibility of this book with on the summer solstice, as well as the team at Icon Books, including Duncan Heath, James Lilford and Robert Sharman. I would also like to thank the numerous press officers, scientists and engineers who have given me many invaluable insights into the world of fusion energy and provided me with great support throughout this project. These include Laban Coblentz, Michael Loughlin and Mario Merola from ITER, Rob Buckingham, Chris Dorn, Nick Holloway and Nick Walkden from the UKAEA, Si-Woo Yoon from the KSTAR programme, Doug Parr from Greenpeace, Breanna Bishop from the LLNL, Daniel Alcazar and Alan Carr from LANL, Neal Singer and Dan Sinars from Sandia National Laboratories, Beate Kemnitz and Thomas Klinger from the Max Planck Institute for Plasma Physics, Mike Forrest, Randall Volberg from Type One Energy, Christos Stavrou of Fusion Reactors Ltd, Britta Weddeling and Jannik Reigl from Marvel Fusion, Tanner Horne from Horne Technologies, viiiChris Ajemian, Scott Brennan and Derek Sutherland from CTFusion, Simon Redfern of Motive PR, Richard Dinan of Pulsar Fusion, Abbey Goodman of TAE Technologies, Jessie Barton from Helion Energy, Stephen Hasley-Mead from Tokamak Energy, Eric Lerner and Ivy Karamitsos from LPPFusion, Jan Kirchhoff and Warren McKenzie from HB11 Energy, Danielle Johnson from General Fusion and Chris J. Faranetta from NearStar Fusion.
Finally, I would like to thank friends and family who have helped in various ways with this book, including David Culpeck, Andrew Fisher, Paul Parsons and my mother Joan.
CONTENTS
INTRODUCTION – HERE COMES THE SUN
From the earliest times, the Sun has held a fascination for us. Some early civilisations went as far as worshipping Sun gods – such as the Ancient Greek god Helios, who was believed to drive a chariot across the sky every day, while the Ancient Romans worshipped the Sun itself. Scientific study of the Sun also dates back centuries, with the Italian scholar Galileo Galilei one of the first to observe sunspots in 1610 using something invented just a couple of years before – a telescope. We are now in an era where there is a different type of focus on the Sun. For the past few decades, we have been striving to harness the same physical process that creates the Sun’s energy – nuclear fusion. The aim is to provide our planet with a much-needed clean energy source and help meet global carbon reduction targets.
Of course, we are already harnessing solar energy for power generation via the familiar technology of solar cells. These provide a valuable renewable energy source, and scientists are currently working on developing a new generation of these useful devices. The intention is to create solar cells 2that generate more power, last longer, work in duller light and use light from a broader range of the Sun’s spectrum. By contrast, in a fusion reactor we wouldn’t be using the Sun’s own energy to generate power. Instead, scientists and engineers are attempting to create what essentially amounts to a mini-Sun down here on Earth that operates at staggeringly high temperatures of around 150 million degrees Celsius (270 million degrees Fahrenheit).
This Sun-in-miniature would give out its own power via the nuclear fusion process. But we would not use its power directly. Instead, just as in current nuclear power stations, the heat generated by the nuclear reaction would be used to boil water, creating steam that drives turbines, which in turn produce electricity.
There are several features of fusion energy that make its use for electricity generation a very attractive prospect. Firstly, it is a clean energy source, emitting no greenhouse gases. Secondly, it could provide almost limitless quantities of power. It is also much safer than nuclear fission – which is the process that existing nuclear power stations use to generate electricity – and it creates no long-lived radioactive waste, which is currently a costly and problematic by-product of nuclear power generation. In addition, fusion power would enable countries to meet their own energy needs rather than importing either the raw materials to generate electricity or the power itself. In short, the development of fusion power plants would revolutionise global energy generation.
With the 2021 Intergovernmental Panel on Climate Change (IPCC) report stating that scientists are observing changes in the Earth’s climate in every region of the planet, work towards new, clean energy sources seems more important, and more pressing, than ever. According to the report, 3‘Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of thousands of years.’ But it also says that ‘strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change’. So, there is still a chance to alter course, and many countries already have targets in place to cut the harmful emissions driving these unwanted changes to our planet. Fusion power plants could provide a powerful ally in reaching the ambitious emission reduction targets required.
Equally ambitious are the fusion experiments under way that may lead to this hoped-for new generation of power plants. The largest of these is the ITER (‘the way’ in Latin) experimental reactor being built in Cadarache in southern France. This has 35 nations pooling funding and scientific expertise – including the 27 member states of the European Union plus Switzerland and the UK, China, India, Japan, South Korea, Russia and the United States. ITER will never generate electricity, but it aims to demonstrate all the scientific and technical steps required to build commercial fusion energy power plants.
While ITER is by far the biggest of the multinational projects attempting to harness nuclear fusion for electricity generation, it is by no means the only contender in the race. Many countries have, or have had, their own research reactors. These include the Joint European Torus (JET) at the Culham Centre for Fusion Energy in the UK, which was first fired up in 1983, the now decommissioned Tokamak Fusion Test Reactor (TFTR) in the United States, which broke several records during its fifteen-year lifespan, the Chinese Fusion Engineering Test Reactor, which was powered up in December 2020, and the Korea Superconducting Tokamak 4Advanced Research (KSTAR) project. KSTAR is a pilot device for ITER and, as we will see later when we look in more depth at these projects, set a new world record in November 2020 for one of the key stages in fusion reactor development.
Then, as we will also explore, there are the private companies fielding fusion contenders. Some of these have high-profile backers and collaborators, such as Canadian company General Fusion, which has funding from Amazon’s Jeff Bezos, and TAE Technologies, which is in partnership with Google.
Not all of these projects are taking the same technological approach. As we will discover, there are different ways in which nuclear fusion reactions can be triggered and then contained, and multiple variants on the main approaches. No one is yet sure which approach will win out. Or, indeed, if a range of methods will be needed to help secure our future energy needs.
Along the way, the reactors look set to become spectacles in themselves. The sheer scale of ITER’s reactor, for instance, with its 1 million components, weighing in at a combined total equivalent to the weight of three Eiffel Towers, is difficult to envisage. Meanwhile, General Fusion have employed award-winning architecture studio AL_A, whose previous commissions include the Victoria and Albert Museum Exhibition Road Quarter in London, to work on the design for their prototype power plant near Oxford in the UK.
Yet it’s not just power stations that are on the cards. There is the potential for fusion-driven rockets to provide the transport for future interplanetary travel, including missions to Mars. And various technologies developed to help enable fusion energy studies to progress, such as the 5advanced robotic systems we will hear about in Chapter 7, have applications in other research or industrial settings. But the main goal of most fusion projects is to generate clean, sustainable power for our planet.
This rendering shows how General Fusion’s UK Fusion Demonstration Plant will look when completed.
AL_A for General Fusion
From the physics breakthroughs of the early 20th century that revolutionised our understanding of atoms, to the horrors of atomic weapons and the Cold War. And from the switch in the late 1950s to seeking peaceful applications of nuclear technology, to the latest experiments working towards fusion energy. This is the story so far of our quest to generate electricity from nuclear fusion. 6
1
WHAT IS FUSION?
The core of the matter
The challenge facing the teams trying to pave the way for nuclear fusion power plants is anything but small. To begin to comprehend its scale it is useful to first understand the fusion process. The best place to start with that is by looking at the atomic nucleus itself. This, by contrast, is most definitely small in nature.
It is amazing to think that just over 100 years ago, no one had even heard of atomic nuclei. Their existence was not suggested until May 1911, thanks to some experiments by students and colleagues of the New Zealand-born physicist Ernest Rutherford, carried out at the University of Manchester. Rutherford’s analysis of their results provided a huge breakthrough, not least because it overturned in a stroke some of the groundbreaking earlier work by J.J. Thomson, the then head of the Cavendish Laboratory at the University of Cambridge (a position Rutherford would 8go on to fill in 1919, having previously studied there under Thomson from 1894 to 1897).
At the time of Rutherford’s breakthrough explanation, the leading model for the atom was British physicist Thomson’s so-called ‘plum pudding’ model. Physicists often use what are known as ‘models’ to explain complex processes. These models are descriptions of physical effects that help them visualise and study what is going on. In Thomson’s model, every atom consisted of negatively charged particles, known as electrons, sat inside a spherical volume that was positively charged. The electrons could therefore be imagined to be a bit like the raisins dotted around inside a plum pudding with the main pudding mix representing the positively charged volume. Hence the model’s nickname.
This had been a big leap in scientific understanding in itself. For centuries before, stretching right back to Democritus in Ancient Greece, scientists and philosophers had defined the atom as the smallest particle of matter that could exist. Thomson’s experiments, in the closing years of the 19th century, had blown this idea out of the water. In 1897, he revealed the presence of electrons inside atoms while studying cathode rays. These then mysterious rays came from the negative electrode, known as the cathode, when a voltage was passed between it and the positive ‘anode’ electrode while both were sealed in a vacuum tube. At the time Thomson began these studies, some scientists thought that cathode rays were a form of radiation. Others believed them to be a stream of negatively charged particles. If the latter was the case, the particles would be deflected by both electric and magnetic fields, and you could work out what type of electric charge they had by observing the direction of the deflection.
9Suspecting the cathode rays might indeed be composed of particles, Thomson applied an electric field to the tube via a second pair of electrodes. Sure enough, the cathode rays bent, and in a way that showed the ‘rays’ to be particles with a negative charge. Thanks to further experiments Thomson was able to determine the ratio between the charge and the mass of these negatively charged particles, which later became known as electrons.
This result kick-started a whole new area of scientific study – subatomic physics. But within a few years Thomson’s student Rutherford was about to make another major step forward and show that the Thomson version of the atom was at best only part of the picture.
Having previously studied at Canterbury College, Christchurch, in his native New Zealand, Rutherford came to England to take up a scholarship at Cambridge University in 1895. Back home in New Zealand, he had been working on high-frequency magnetic fields. But after initially continuing this work at Cambridge, he switched to studying the effects that the then newly discovered X-rays had on air. In 1898, Rutherford moved country again, becoming a professor at McGill University in Canada. Here, he worked with Frederick Soddy on radioactivity.
The year after arriving at McGill, and before starting his collaboration with Soddy, Rutherford had shown that radioactive elements gave out two different types of emissions. He named these alpha rays and beta rays. By 1900, he had shown there was a third type of radiation emitted by radioactive substances – gamma rays.
It is difficult to overstate the impact this one man had on early 20th-century physics, and indeed on the story of fusion. Nuclear fusion experiments could simply not have 10come about without the fundamental physics discoveries made by Rutherford and his students and collaborators.
For instance, Rutherford’s later work with Soddy revealed radioactive elements were changing into other elements – a process known as transmutation. While Soddy continued that work, Rutherford moved to looking at the alpha radiation emitted from radioactive elements.
In 1907, Rutherford had made another physical move, this time back to the UK to the University of Manchester. This was an exciting and fast-paced time for physics, and for Rutherford himself. Just a year after his arrival, he invented the Geiger counter with his colleague, German physicist Hans Geiger. Their initial version, the forerunner of the devices still used for detecting radioactivity today, was designed to detect the alpha particles they were studying. It consisted of a gas-filled tube threaded through with a wire along its longest axis. This wire had a high voltage running along it, and when alpha particles passed through the gas, they initiated a reaction that produced a pulse of current that could then be read on a meter.
With the help of their new device, Rutherford soon showed the alpha radiation (now known as alpha particles) was composed of helium atoms lacking their two electrons, which left them positively charged. It would take a few more experiments before it became clear just how significant this result was to be.
The 1909 experimental set-up that was to lead Rutherford to a breakthrough in understanding the structure of the atom was fairly simple. It consisted of a radon source, which is radioactive and gives out alpha particles, a lead screen with a small hole that let through a narrow beam of alpha particles and a thin piece of gold foil. These, along 11with a detection system, were housed within a cylindrical tube. Air was pumped out of this tube so that a vacuum was created inside, which allowed the alpha particles to travel further than they could have done through the air. The main component of the detection system was a glass screen coated with zinc sulphide, which emits a tiny flash of light whenever an alpha particle hits it. This detection screen was mounted at the end of a microscope that could be rotated through different angles.
Once the experiment was under way, the beam of alpha particles was directed towards the gold foil. The scientists expected to see the alpha particles either passing straight through the foil, or for their paths to be deflected slightly. The latter would occur thanks to the positively charged alpha particles interacting with the positive electric charge within the gold atoms of the foil in a similar way to the like poles of a magnet repelling each other. Any alpha particles shooting out from the foil at the correct angle to fall onto the zinc sulphide screen created tiny flashes of light as they hit the screen. So, by rotating the microscope with its attached detection screen around the apparatus, members of Rutherford’s team were able to see what angles the alpha particles were being deflected by.
They observed that some of the alpha particles were indeed passing straight through the foil at the same angle they entered or were being slightly deflected by the positive charge within the gold atoms. The latter so-called ‘scattering’ of the particles was just as Rutherford had predicted. But what the team – which included Geiger and English–New Zealand physicist Ernest Marsden – had not bargained for was seeing flashes of light, indicating that a small number of the alpha particles had been bounced back in the direction 12they had come from. How could this be possible from the atom of Thomson with its positive charge spread around rather weakly throughout its volume?
The answer is it couldn’t. Thomson’s old ‘plum pudding’ model was now past its expiry date. These new observations could only be explained if atoms had a concentrated area of positive charge at their centres. The positively charged alpha particles would then be scattered off this region of positive charge like a ball bouncing off the edge of a pool table. This was exactly what was being seen in the experiment. So, in 1911, Rutherford proposed that every atom consisted of a positively charged nucleus surrounded by negatively charged electrons. Although this is a simplification, this is the basis of the model that is still taught to school pupils today. Rutherford would later state that the experimental result ‘was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you’.
As well as revealing the existence of the nucleus, this experiment also showed that it had to be small. Really small. This is because only a tiny percentage of the alpha particles were deflected by large angles, meaning that there was a low probability of colliding with a nucleus inside a gold atom. The vast majority of the alpha particles were not interacting with this positively charged nucleus and just sailed on through the gold foil. These results could only be possible if each nucleus took up a very small volume within each atom. In fact, we now know that the width of a nucleus is around 100,000 times smaller than that of the atom it sits within.
Quite literally in a flash, this experiment and the subsequent new description of the atom completely revolutionised physics. Fortunately for science, Rutherford was not done there. 13
Remaining neutral
In 1920, Rutherford predicted the existence of neutrons – subatomic particles with zero electric charge – which as we will see later have important implications for fusion reactors. By this point, Rutherford was head of the Cavendish Laboratory at Cambridge. In 1932, this was where his colleague, assistant director of research James Chadwick, discovered the neutron. British physicist Chadwick won a Nobel Prize ‘for the discovery of the neutron’ in 1935, an honour which Rutherford had himself received in 1908 ‘for his investigations into the disintegration of the elements, and the chemistry of radioactive substances’.
It was later figured out that nuclei consist of positively charged protons and electrically neutral neutrons. So, the simplest version of the currently accepted model of the atom, with its negatively charged electrons orbiting around a positively charged nucleus, is a product of these early 20th-century experiments and explanations.
As is often the case, there is an exception to the rule. In this instance, the model of the nucleus containing protons and neutrons holds for every type of atom except hydrogen. Hydrogen is different in that the nucleus of its most common form houses just the one proton with no neutrons to keep it company. If you look at the Periodic Table of the elements, you will see that hydrogen occupies the first spot in the table and is numbered one. You will also notice that the next element helium has the number two associated with it, lithium three and so on, rising in increments of one through the table. This number is the so-called atomic number. For a given element, the atomic number represents the number of protons in the nucleus of each of its constituent atoms. 14
