This episode is sponsored by Audible Ever since humans figured out that the Sun is powered by hydrogen fusion, we’ve imagined
controlling the process and powering our civilization with miniature Suns. But as it turns out, the Sun is highly impractical,
and we’re going to need to design something a lot better... So today we are looking at Fusion Power, how
it might work, what’s holding up this technology, and what cool new options it opens up for
our civilization. Many of these possibilities are less obvious
than simply cheap electricity or fast spaceships, but just as important. This is a topic we mention in passing a lot
on this channel as a keystone for many of our future technologies and pathways, so as
we progress I’ll pop up the cover art for the relevant episodes. I thought we should start by addressing the
challenges with achieving a working fusion reactor. There is an overused saying that makes me
scowl whenever I hear it; that Fusion is the technology of 20 years from now, and always
will be. Fusion as a serious concept is a lot newer
than many of our other power sources, and has progressed neither particularly faster
nor slower than most of them. Just as an example, solar power – itself
an example of harnessing fusion from the Sun – has only recently become economically
viable as primary power source. Back when I was a kid in the 1980s, we really
only saw photovoltaics on very low energy, portable devices like calculators, as it was
very expensive and inefficient. It was not new technology then either, way
back in 1876 it was found that you could generate electricity by exposing selenium to sunlight,
and Charles Fritts made the first solar cells in 1883. So it took over a century before we even had
good enough solar to consider commercial usage of it. It was also half a century after those first
solar cells before we even knew what fusion was, and before that we thought the sunlight
running those primitive solar cells was caused by gravitational collapse. We had our first working artificial fusion
source a mere generation later, with the Hydrogen Bomb in 1952. Similarly, while Ben Franklin did his famous
kite flying experiment with electricity in 1752, it was half a century later before Alessandro
Volta, for whom the volt in named, built the first electric battery. Then it was a couple more generations before
we saw the first electric generators and engines, and a couple more before Edison and Tesla
hit the scene. Considering how hard it is to experiment with
fusion, something which only naturally occurs in the heart of stars, it isn’t all that
surprising that we still don’t have a working fusion reactor less than a century after we
even realized such a thing as fusion existed. It’s not helpful when folks go around talking
about 20 years from now like that was useful or meaningful, when its timeline is still
shorter than the development of many other technologies, from computers and rockets to
other power generation mechanisms. The other big issue is that you need large,
high tech, and expensive facilities just to experiment with fusion in a serious way, which
usually means anytime you learn something new from an experiment, you need around 20
years just to digest and theorize about that new data, draw up a new experiment, pitch
a grant proposal for major government funding to build new massive and expensive facilities,
and then build them, before you can get your next set of data to refine your models, rinse
and repeat. Now as to the mechanism, there’s a bit more
to it than hydrogen slamming together and turning into helium at millions of degrees. At high temperatures, the electrons get stripped
off atoms and you have a plasma of atomic nuclei. In the case of common hydrogen-1, the nucleus
is just a single proton with no neutrons. To fuse two protons together you first have
to overcome the repulsion of their positive charges, and the closer you get them together,
the greater the force and energy involved. That energy is what we call the Coulomb Barrier. The normal means for supplying that energy
to move the particles together at high speed can be done in a particle collider, but the
method used in stars is just heat, which is just a measure of how fast individual particles
are traveling. One of the things that slowed us down on figuring
out what powered the Sun was that its temperature isn’t actually high enough to overcome that
Coulomb Barrier. That takes various quantum effects, and so
does binding the protons together once they get there. And here’s where we get into what makes
hydrogen fusion so tricky, it’s a hurdle that comes early in a fairly complicated process. When a pair of protons get close enough together,
the Strong Nuclear Force will bind them, kind of, into a very unstable isotope called a
diproton, which nearly always splits right back into a pair of protons. Very rarely—and here’s where quantum mechanics
comes in—that diproton instead emits a positron and decays into a nucleus of deuterium, a
proton-neutron pair. From there, there are actually a number next-steps
that might take place, some of which is the deuteron might fuse with another proton or
deuteron, to produce various intermediate isotopes that undergo fusion and decay reactions
of their own… before finally producing nice stable nuclei of Helium-4, which have two
neutrons and two protons. But the difficult hurdle to clear, the bottleneck
in the whole process, is that rare decay of a diproton into deuterium. That bottleneck is the reason stars take billions
of years to use up their hydrogen. The half-life of a proton in the core of our
Sun before it is fused into deuterium is about a billion years; which is to say, bouncing
around at that temperature, in the core where fusion is actually taking place, any given
proton has only coin flip odds of fusing into deuterium in a billion years, even though
it would fuse briefly into diprotons several times along the way. That’s a good thing for us, because we wouldn’t
be around if the Sun burned fuel faster than that. Indeed bigger stars create a higher pressure
at their cores resulting in faster fusion, so they have shorter lives precisely because
they have more fuel. Even then it’s pretty slow for our purposes. It doesn’t come up much in our discussion
of fusion as a power source, but if you could replicate the conditions inside the Sun in
some reactor down here on Earth, with several tons of fusion fuel inside it, that would
release perhaps a billion, billion joules of energy over the course of a billion years. Which means it could run a light bulb. And while it would last a billion years, you’d
have to expend energy to maintain and run the thing too. That’s the two foremost challenges of fusion
reactors: getting a net positive energy gain, and dealing with all the damage to the components
and containment vessel from the radiation. Fortunately, the past few decades of research
have yielded improvements in the efficiency of the design and durability of the alloys
we use in fusion R&D, though still not enough. But again, such a reactor doesn’t interest
us much as a power source, any more than a H-bomb does, so we need something that can
run a lot hotter. People talk about how hard it is to replicate
the conditions inside a star, but we’re way past that. We usually estimate the temperature of the
Sun’s Core at about 15 million Kelvin, while those Tokamak Fusion Reactors you’ve heard
about can run at 150 million Kelvin, 10 times hotter, and we’ve actually briefly produced
temperatures in the trillions in labs by ramming particles together. So again, we’re not trying to replicate
the center of our Sun, because that’s not good enough. We’re also not trying to do proton-proton
fusion much right now. The default approach is to use deuterium or
tritium, hydrogen isotopes with a proton and one or two neutrons, or helium-3, with two
protons and one neutron, or lithium, which has three protons. These isotopes have lower Coulomb Barriers
to overcome to produce a fused particle and release energy, so they are our first step. Deuterium-Deuterium, or D-D Fusion, is often
seen as the most attractive because Deuterium, while rare compared to normal hydrogen, is
still very common on Earth, whereas Tritium has a half-life not much over a decade so
it’s hard to find, and helium is quite rare on Earth and Helium-3 even more so. Handily if you do have a fusion reactor, you
can build ships that can quite quickly and economically go fetch these rarer fuels from
our various gas giants, and Helium-3 is an attractive fusion fuel for reasons we’ll
get to in a bit. Remember how difficult it is to produce deuterium
from protons? When we fuel a fusion bomb or reactor with
deuterium, we are taking advantage of the fact that dead stars, of whose material our
planet is made, already took care of the most difficult part of fusion for us. Thanks, Universe! Your ideal fusion reactor though would run
basic hydrogen all the way through the various heavier fusion chains to iron, releasing energy
at each step. This series of reactions can be considered
the ultimate goal as it’s the most efficient use of the fuel, but achieving such a thing
is a long way off. I should note that not all fusion reactions
produce energy. In general those resulting in elements heavier
than iron, are net negatives. These reactions are easier in some ways too. It’s fusion when you add neutrons to uranium-238
to turn it into Plutonium-239, for instance. So regular Fusion is hard to do, particularly
as we have to do it better than stars can, and with far less mass and gravity to work
with. So what are the methods? Well first there is the H-Bomb, which uses
a fission explosion to make fusion occur much in the same way we use conventional explosives
to set off the fission reaction. We can make power with this, and I mean usefully
too. You make small fuel pellets of plutonium and
your fusion fuel, essentially small H-Bombs, and set them off in something that can absorb
the energy, like water or preferably molten salt, which you then tap for power more slowly
using conventional heat engines like many power plants use. Then all you have to do is set a new one off
every so often to reheat the liquid medium. This is a fission-fusion hybrid, arguably
a chemical-fission-fusion hybrid since it uses chemical explosives to ignite the fission
to ignite the fusion. But bomb-grade explosives aren’t cheap,
and neither is weapons grade uranium or plutonium for the fission or deuterium and tritium for
the fusion. At least the tritium anyway, deuterium actually
is relatively cheap and more so when you have an abundant cheap power source for separating
it from water. So it’s pricey, but the costs would get
lower with scale, these need to be big plants and the bigger the better, ideally ones powerful
enough you only needed a few per country, but at least it lets you get a lot more juice
out of your fissile materials. Whether or not it would be competitive or
cheaper than existing power is debatable, but that wouldn’t necessarily matter if
you’re running out of material for those existing sources. Now you could make smaller bombs for smaller
reactors using transuranic elements beyond even plutonium, but that wouldn’t be for
Earth based power, but some place where you needed a small and short lived but powerful
reactor. These aren’t high-tech futuristic technology,
incidentally. I’d say we could build one tomorrow, but
the scale of such a plant would imply many years of construction to make something big
enough and shielded enough to absorb even small blasts. However this sort of approach is more attractive
if you’ve got cheap superconductors since it means you can have very few but very large
plants, or ones in isolated areas, without losing lots of your energy to resistance in
your electric wires. Of course superconductors also make awesome
magnets, which is the keystone of the best known approach to fusion: tokamaks and other
magnetic confinement systems. Hot hydrogen and helium turned into plasmas
are charged particles, so very susceptible to magnetic fields, and so we can use them
to contain our plasma. This is important because that plasma needs
to be hundreds of millions of degrees, and even our best alloys can only handle thousands
of degrees, so if the plasma could touch the containment vessel, it would slag the whole
thing. Your basic Tokamak is a big toroid, or donut,
created by using magnets to contain the plasmas and to exert force on them to speed up and
start slamming particles around so they get hotter. The primary problem is that doing this takes
energy, hence the concept of ‘break even’. So you need a reactor that produces more energy
than it takes to heat everything up. The next problem is actually utilizing that
energy, and the general assumption is that you’d be absorbing the radiation given off
as heat in the containment vessel, and exchanging it with coolant with which you’d then generate
power through a normal heat engine. There’s a lot of losses in such a process,
which means your real break-even, in a practical engineering and economic sense, is even higher. The next problem after that is that you are
irradiating that containment vessel. You have to if you want to get power after
all, and while magnets are good at containing protons and electrons, they don’t protect
against gamma rays, neutrinos, or neutrons, all of which are being produced, though the
neutrons are the major concern. None of these are thought to be unconquerable
problems, and we’ve been slowly approaching the break even point over the years, but we’ve
also been encountering other issues as we progress. The Tokamak tends to be the default fusion
reactor everything else gets compared to, and comes in other shapes than toroids, like
spheres, but it isn’t the only approach. Even focusing only on magnetic confinement,
there are many other variations. Another method is inertial confinement, which
usually uses a laser or charged matter beam to slam enough energy into a fusion-fuel pellet
to ignite fusion, and is conceptually pretty similar to the technique we discussed for
making Kugelblitz black holes, only a lot easier. This is the approach the National Ignition
Facility uses. Another confinement approach is Inertial Electrostatic,
which uses electric fields to speed up the plasma, rather than magnets, though the Polywell
approach combines the two. You’ve also got magnetic and electric pinch
approaches. A pinch in this context is where you get some
electric filament, such as a plasma, and compress it magnetically, and you actually see this
in the sky a lot with both lightning bolts and the aurora. There’s a few types of pinch designs, but
the main one is the Z-pinch, which you might recognize from the Z-Machine, or Z Pulsed
Power Facility at Sandia National Labs. This is also an example of pulsed power, same
as the h-bomb route, where the idea is to produce it in quick enough bursts that it’s
essentially continuous for practical applications. There are many other methods, but I’d like
to get on to the practical impact of fusion so we’ll skip them, though I don’t want
to imply their omission reflects badly on them. While the idea of “Cold Fusion” has a
deservedly shady reputation, a lot of other fusion experiments get tainted by association
with that, usually unfairly. The last thing I want to mention real quick
is helium-3 and aneutronic fusion. Most fusion approaches produce a lot of neutrons
which damage and irradiate things, and we don’t want that if we can avoid it. Helium-3 produces a lot less neutrons in its
various fusion chains like helium-helium, helium-deuterium, or helium-lithium. It’s harder to do than the various deuterium
and tritium reactions, but it would permit longer-lived and lighter reactors, which makes
it especially tempting for spaceship engines. There is very little helium-3 on Earth, and
the Moon isn’t really a great source of it either due to its very low concentration
in the regolith, but there is plenty of it out in the gas giants and that could easily
drive colonization of Uranus and Neptune as we discussed in colonizing Neptune, as they
have the highest concentrations, and plenty of deuterium too. The key thing is you don’t need much of
it on the Earth or the Moon to start using it, since the moment you have a fusion reactor
good enough for a spaceship, you’ve got a spaceship that can easily run back and forth
to Neptune to collect Helium-3, and a reactor that can easily power refineries and habitats
around those gas giants, far from the Sun. Indeed it’s good enough for interstellar
travel too, potentially allowing speeds of 10-20% of light speed, though more realistically
probably less than that. Check out Atomic Rockets if you want a detailed
breakdown of the various hypothetical fusion drives, Winchell’s website goes into the
details without bogging it down in techno-speak. Obviously the biggest application for fusion,
normal or aneutronic, is power generation, since down on Earth you don’t care about
power-to-mass ratios. Fusion rockets are the other as we just mentioned,
but it’s not so good for ground-to-space ships, because while you can accelerate slowly
in space, which fusion is really good at, you really need high thrust to get out of
an atmosphere, and your default high-efficiency, high-power fusion torch drive does not radiate
its containment vessel to warm it up and run a heat engine or superheat some propellant,
but rather it dumps all that hot plasma out the back as the propellant, which is decidedly
unhealthy. Not that standing in a normal rocket flame
is very healthy either, but a superhot plasma exhaust with lots of gamma rays and neutron
flux is a whole new level of hazardous, especially considering such ships probably need to be
quite large too. They also might not be great for power generation
in space, at least reasonably near the sun. Fundamentally, while fusion is very energy
dense, fusion power is really not. You’re heating something up to run a normal
heat engine, and in space you could achieve the same thing by taking a bunch of thin parabolic
mirrors and aiming them at that same working medium. Considering how cheap a mirror is, how much
sunlight there is, and how much empty space there is to put mirrors in, you are probably
going to find it’s cheaper in the inner solar system, in terms of both money and mass
and for stationary power generation, to just use solar. Though as with every power generation method,
there’s likely to be occasions where one system outperforms another for a specific
use, even if in most other cases it doesn’t. Now, down on Earth, what’s the advantage? First you’re not beaming any energy down
from space, as we discussed in power satellites, or dealing with clouds or night time for ground-based
solar. Second, even if you are limited to deuterium,
or even helium-3 and tritium, you’re going to get a lot more energy from those stockpiles
on Earth or throughout the solar system than you would from chemical or fission fuels. There is no such thing a truly renewable power
source, but we count the sun as the next best thing, and fusion parallels or beats that. It also doesn’t generate the highly radioactive
waste that fission does, though I should note that the fear of radioactive waste from fission,
especially with modern methods, is decidedly exaggerated. It also doesn’t produce carbon dioxide,
nor does extracting deuterium from ocean water cause any ecological issues associated to
mining. In fact, since carbon dioxide from fossils
fuels is produced by adding oxygen to hydrocarbons and producing water and carbon and energy,
it’s worth noting you can run that process backwards, just paying energy to do it. That’s not advanced science, sucking carbon
dioxide and water out of air to make hydrocarbons and oxygen, in reverse, is quite easy. It’s just going to take you more energy
than you’d get by burning it. But if you’ve got a huge source of energy,
though not a mobile one, you suddenly can start making gasoline out of air as a nice
compact, carbon neutral power source. Chemical fuels are awesome ways of generating
power compared to even our best modern batteries, so if you can synthetically produce a cheap,
unlimited, and ecologically safe supply of them, the impact would be huge. It could be carbon negative too, since you
could dump that carbon out of the air into mine shafts or maybe make diamonds or graphene
out of it. Needless to say those are valuable to us too
but diamonds might be energy prohibitive to mass produce as a construction material, unless
you have good fusion reactors. There’s also aluminum though, and for that
matter steel. Aluminum is awesome stuff for building many
things but cost prohibitive because it takes a ton of electricity to make. Similarly while you do need carbon for steel,
the main use of it in steelmaking is for heat, so fusion lets you make both cheaper then,
and if you are using it to run carbon sinks, it lets you get away with using concrete to
your heart’s content without carbon concerns. It also makes vertical farming or cold-climate
farming in greenhouses economically viable, as you can now run lighting and heating at
competitive costs to natural open air farming, amplifying the amount of food you can get
out of a chunk of land. You can also desalinate water and pump it
anywhere, with that kind of energy, allowing the conversion of arid deserts and tundras
for agriculture. Similarly, with cheap power, you can recycle
virtually any material economically and extract new metals in more environmentally friendly
ways. We’re only touching on the options available
which we’ve discussed in a lot of our episodes, particularly the Impact of Fusion episode
in our show’s first season, and the Arcologies & Ecumenopolises episodes that looked how
far you can go with vertical farming when you have a ton of cheap energy. This is a power source that basically eliminates
most ecological problems, directly or indirectly, allows interplanetary and even interstellar
space travel, and lets you terraform planets or build and light and heat artificial habitats. I think sometimes the skepticism towards fusion,
as mentioned at the beginning, has to do not with it developing particularly more slowly
than most other technologies have, but, rather, in part from its breakthrough and wonder status,
it being seemingly miraculous. Now, there are still some downsides and limits. First off, the cost of power is not just the
cost of fuel, which is not free even for fusion, especially if you need to use rarer isotopes
than deuterium or plain hydrogen. Power Plants need maintenance, electric grids
need maintenance, but you’d expect to see a big drop in cost and possibly more of a
subscription approach rather than a per unit approach, like we tend to do with phones and
internet. You pay for access to a certain amount of
power whether you use it or not, rather than per unit of energy, which might mean big industrial
users get their energy very cheaply, as everyone’s really paying for their electric lines and
building & maintaining the power plant. You’d also have huge knock-on effects to
the economy, when gasoline, fertilizer, construction material, and many manufactured goods all
get cheaper. The price of power might only get cut in half,
but if everyone is earning twice as much and paying half as much for many goods, it’s
not just a tiny cut in your electric bill. It’s an economic snowball, and it’s why
I usually count fusion as one of the handful of technologies that if you’ve got it, either
by itself or maybe with one other, instantly kicks you into a post-scarcity civilization. Putting it bluntly, within a couple decades
of us developing a viable commercial fusion reactor, even one that can only match modern
energy costs, whether that be tomorrow or a century from now, will almost certainly
push humanity into an era of universal prosperity, since so much of what’s holding us back
from that today is the limited stockpiles of fuels and the worries over their usages. Of course it’s not a total end to ecological
worries like global warming either. Greenhouses gases trap heat, but if you’re
using enough power, green or not, you can start warming up. Fortunately you’d need to have trillions
of people living on Earth before that was a serious issue and we discussed some ways
to get around that in Ecumenopolises, Planet Wide Cities. One of those approaches was great big space
towers or orbital rings for radiating heat, or bringing food and materials down to Earth
cheaply, so you could reduce how much heat you made here on the ground, and active support
structures, which require a lot of power, is something fusion is great for too. And that’s fusion in a nutshell. Unsurprisingly, the power of the Sun, when
we get it working, offers us a very bright future… Fusion is one of those technologies, like
smart automation, that offers a key to unlock the galaxy to us and make our own world into
a paradise. Many authors tend to write dystopian science
fiction to add tension and challenge but while those often make for great stories, they often
feel very unrealistic to me, even if they have good hard science in them. There’s more to realistic science fiction
than just getting the science part right, the civilizations on display have to feel
realistic for the setting and technology too, and of course Paradise is rarely without it’s
own new challenges and can be a bit subjective. One of my favorite authors in that regard
is Peter F. Hamilton, particularly in his Commonwealth Saga beginning with the novel
Pandora’s Star. Set in the 24th century, the book shows us
many fantastic and immense ideas, but also gives a close look at day to day life and
how those wonders, like energy and land abundance and life extension, begin shaping that civilization. Later books in the series follow that civilization
into future centuries. The series is also narrated by John Lee, who
as I’ve mentioned before is my favorite audiobook narrator and as usual he gives an
excellent performance that only improves an already excellent series. You can get a free copy of Pandora’s Star
at Audible.com/Isaac or text Isaac to 500-500. Audible offer a 30 day free trial, but each
month you’re a member you now get a free audiobook and 2 audible originals, and those
credits rollover to the next month or year and stay yours, along with any books you got,
even if you later discontinue your membership. And with their convenient app, you can listen
on any of your devices and seamlessly pick up where you left off, whether you’re listening
at home, commuting, running errands or off jogging or at the gym. Audible makes it cheap and easy to access
a vast collection of amazing stories. So a couple quick announcements before we
hop into the schedule for the rest of the month. First, an update and apology, back around
the beginning of the year I grabbed a post office box after requests I give folks a non-electronic
way to send me things and obviously didn’t want my home address up on the internet but
some confusion during the setup resulted in a lot of that getting returned to sender and
I didn’t find out for months. That should be fixed now, and the address
is still Isaac Arthur at PO Box 529, Geneva, Ohio, 44041 in the United States. Second, we have a new extra episode up on
Nebula about the Butterfly Effect, and I’ll leave the promo link in the episode description
so you can use the 7-day free trial to check that out, and our previous one, the Paperclip
Maximizer. Nebula is a new streaming service a bunch
of us creators got together to make as an experimental alternative hosting platform
to give us more flexibility in content and control of our content and its launch exceeded
even our most optimistic expectations. There’s a lot of material I and other creators
on Youtube mostly don’t create because we worry about getting punished by the recommendation
algorithms and Nebula is designed to help us with that and we’ll keep adding features
as it grows. In general the stuff I upload there that is
just bonus episodes will migrate over to Youtube after a couple months but other content like
extended commentary or behind the scenes material that folks ask for but which would get butchered
by the Youtube Algorithms will likely stay exclusively there, and we’ll get channel
specific links for Patreon supporters integrated into that in the near future too. As you probably noticed, we had a lot more
callback to prior episodes than normal, as this topic is very integrated into a lot of
our episodes, and these days there’s about 200 episodes, many look at things which seem
nigh impossible but technologies like Fusion might one day bring them into existence. With that in mind, we’ll be having our 200th
official episode, “Things which will never exist” in just two weeks. Before then though, there’s another topic
we discuss a lot and that is megastructures or other giant constructs like generation
ships or artificial planets, and something we don’t look at much when discussing those
is how you go about maintaining those and sweep up all the debris you generally need
to clear out to make them or generate in making and using them. So next week we’ll take a look at the untidy
underside of our big bright future in Space Janitors & Megastructure Maintenance. For alerts when those and other episodes come
out, make sure to subscribe to the channel and hit the notifications bell. And if you enjoyed this episode, hit the like
button and share it with others. Also if you want to check out any of those
many past episodes we mentioned today, check out the playlists for the channel here on
Youtube or our website, IsaacArthur.net. Until next time, thanks for watching, and
have a Great Week!
