truly ever could unleash its power on our planet.
Humanity, it seems, has a power problem.
Even as we burn through our dwindling
fossil fuel reserves and climate chaos
intensifies all around us, every year
our energy requirements rise by an
estimated 1 to 2%. The need for a clean,
efficient, and inexhaustible energy
source has never been so acute. For many
decades, this has been the promise of
nuclear fusion. Unlike nuclear
fishision, which splits rare and
unstable isotopes to generate power,
fusion technology aims to replicate the
processes that happen inside our sun,
fusing hydrogen into helium and
releasing a huge amount of energy in the
process. Yet, since fusion was first
talked about as a serious contender for
energy generation in the 1950s,
it has become a cliche that is
perpetually 30 years away from becoming
reality. So, why then does it seem that
fusion is always just out of reach? And
do the new private enterprises that have
recently entered the field really offer
any hope of shaking things up? To begin
to answer these questions, there is no
better place to start than the place
that inspired fusion science in the
first place, our sun.
As strange as it sounds now, at the turn
of the last century, we didn't know what
powered the sun. The source of the heat
and light that sustains all of life on
Earth was a mystery. The leading theory
was that the sun's energy came from
gravitational contraction. Simply put,
the idea proposed that as a star
gradually radiates energy to space, it
cools and so collapses further under its
own gravity, which in turn causes
gravitational potential energy to be
converted into heat in the stars core.
Today, we know that is a genuine
process. Not only is it involved in the
formation of stars, it's also the reason
that the gas giant Jupiter radiates more
energy to space than it receives from
the sun. In fact, the planet is
shrinking by about 2 cm every year under
its own gravity. And as the resultant
internal heat works its way from deep in
Jupiter's interior and out into space,
it drives the intense storms that dance
across the planet's surface. But when it
comes to powering a star, one scientist
realized that contraction didn't stand
up. In a 1920 paper, physicist Arthur
Edington wrote, "If the contraction
theory were proposed today as a novel
hypothesis, I do not think it would
stand the smallest chance of
acceptance." He argued that contraction
would be hopelessly inadequate for
powering a body that radiates as much
energy as our sun. Suspecting that stars
were places in which hydrogen atoms were
cobbled together into heavier elements,
Edington proposed a different source of
energy. Drawing on experiments carried
out by fellow scientist Francis Aston.
Aston had shown that the mass of a
helium nucleus was ever so slightly less
than that of four hydrogen nuclei. So if
a helium atom was just four hydrogens's
fused together, some mass was missing.
Edington believed that this missing mass
was converted into energy by Einstein's
E= MC². And because C, the speed of
light, is such a large number, the
energy generated from even a tiny amount
of mass is huge, meaning fusing hydrogen
into helium would provide more than
enough energy to power the sun.
Edington's ideas were bold and unproven,
but they soon inspired serious
theoretical work. And in 1929, the first
calculations of stellar nuclear fusion
were published by Robert Descort
Atkinson and Fritz Howmans. It turned
out that the sun and all stars were
giant fusion reactors, taking the most
common element in the universe,
hydrogen, and fusing it into other
elements. Starting with helium.
Now replicating this process on Earth
would be hugely advantageous especially
when compared to nuclear fishision. The
process that is used in nuclear power
plants today. Where fishision relies on
splitting large and rare unstable
isotopes such as uranium 235 and
plutonium 239.
Stellar nuclear fusion relies on
hydrogen, an element that is widely
available on Earth through the
electrolysis of seawater. And unlike the
radioactive byproducts of fish that
create a huge disposal problem for
modern nuclear power stations, the
byproduct of stellar fusion is helium,
an extremely useful element.
Thanks to its exceptionally low boiling
point, helium is used to cool the
magnets in MRI machines for scientific
research projects like CERN as well as
in the production of microchips. It's an
essential element that we actually need
more of. So, how exactly do stars
achieve this alchemy of fusing hydrogen
into helium? And how are scientists
going about trying to replicate the
process?
Well, the first thing to consider is the
reaction medium. The stuff stars are
made of. Unlike matter on Earth, stars
aren't even made of atoms and molecules,
where negatively charged electron clouds
orbit positively charged nuclei. Stars
are so hot that electrons can escape
atomic orbits entirely. The resulting
soup of charged particles, ions, and
free electrons is known as plasma. And
it's in plasma that nuclear fusion can
take place.
Now plasma is by far the most common
material in the universe making up well
over 99.9%
of visible that is nond dark matter. But
we are part of the 0.1%.
That small amount of matter in the
universe that's cool enough that in
general electrons confined to orbitals
and chemistry, not nuclear physics,
dominates, allowing cool balls of rock
covered in oceans of water like Earth to
form. For us, creating such conditions,
making plasma that's hot enough to
sustain fusion and containing it is a
considerable challenge. You see, the sun
has one quite literal giant advantage on
its side. It's so huge that the force of
gravity holds the plasma in a near
perfect sphere with pressure at its core
reaching 150 g per cime cubed. So dense
a teaspoon would weigh close to a
kilogram.
The biggest fusion reactor on Earth, ITA
in France, a leading international
project that hopes to be operational in
2034, will use just a few g of plasma
material in a chamber of 830 cubic m.
Because it's under such low pressure,
meaning particles aren't squeezed
together like they are in the sun, this
plasma has to be much, much hotter to
achieve fusion.
50 million° C as opposed to 15 million°
at the core of the sun. Now, fairly
obviously, you can't just hold a
material like this in a container made
of normal matter. If it contacted the
sides, it would cool. Electrons would
condense into atomic orbitals, and it
would no longer be plasma. And of
course, it goes without saying that the
container itself would be damaged beyond
repair. So the plasma needs to be
isolated in a vacuum. Two approaches
have been put forward to achieve this.
The first of which is magnetic
confinement fusion. Because plasma is a
soup of charged particles, positively
charged ions and negative electrons. It
can be manipulated by magnetic fields.
Magnetic confinement takes advantage of
this by using a ring of powerful magnets
to hold plasma in a continuous
donut-shaped blob in which fusion can
take place. There are a number of
different types accelerators and
reversed field pinch devices but the
leading design is called the tokamac.
This is the type of reactor which will
be used at ITA. In contrast, inertial
confinement fusion, the other
confinement method, takes its
inspiration from thermonuclear bombs. It
works by firing lasers or projectiles at
a small pellet containing fusion fuel,
seeking to create temporary blobs of
plasma which release fusion energy only
for a few nanos before the plasma
dissipates. Both of these approaches are
immense engineering challenges requiring
either huge amounts of continuous
electricity in the case of MCF or even
larger pulses of electricity drawn from
banks of capacitors in the case of ICF.
But not only do the huge amounts of
power involved put tremendous strain on
components which have to be replaced
frequently, it means that for a reactor
to be viable, the energy obtained from
the fusion reaction must exceed the
colossal amount of energy required to
initiate it. A considerable challenge.
so, let's get back to the world's energy crisis. As I was saying, fusion reactors
take huge amounts of energy to get
going. Now, you might think, surely once
you have surpassed this feat, you've got
more energy out than you put in. That
would be it. A huge win. After all, the
fuel hydrogen is both cheap and
abundant. But alas, it is not that
simple. And to understand why, we have
to look back once again at our star and
the fusion reactions that only take
place deep inside the stellar core.
It is here in the sun's core that
hydrogen is fused into helium via
multi-step reaction. Firstly, two
hydrogen nuclei or single protons
combine with one undergoing a process
called beta decay to transform it into a
neutron. The resulting neutron proton
pair is a nucleus of a heavy isotope of
hydrogen known as dutarium.
In the next step, another proton
combines with the dutarium nucleus to
generate a helium 3 nucleus.
In the final step, two of these helium 3
nuclei fuse to produce a helium 4
nucleus containing two protons and two
neutrons, also known as an alpha
particle, as well as two protons.
Now, this may sound fairly
straightforward, but it's not. The
reason being that even in the sun
getting two protons to react to form
dutyium the first step of the reaction
is far from easy. Firstly, in order to
fuse the protons must get extremely
close to each other around 10 ^ -15 m
apart. That is so the strong nuclear
force, the force that holds protons and
neutrons together in the nucleus of an
atom kicks in and they are drawn
together. However, for two positively
charged protons, getting this close
means overcoming an immense amount of
electrostatic repulsion. So much so that
even the kinetic energy provided by the
extreme conditions at the heart of the
sun where protons are traveling around
500 km/s
is wildly insufficient.
In fact, protons have only around
1,000th of the kinetic energy they
require to overcome this barrier. It
turns out the only reason the sun is
able to sustain fusion at all is because
quantum effects come into play. Now you
may remember that according to quantum
physics protons don't just act as
particles they also act as waves. This
wave behavior means that in 10 ^ 28
proton proton interactions the protons
can overcome this energy barrier.
getting close enough that the strong
nuclear force pulls them together. This
is called quantum tunneling. But even
when protons are drawn together this
way, there is yet another effect to
contend with. The force that mediates
the conversion of one of the protons
into a neutron is the weak force, which
because it is controlled by the massive
W bzon is very inefficient. This leads
to the more likely product of the proton
proton reaction being a proton pair
which immediately decays back into
single protons.
Together these effects mean that the
rate of proton conversion in our star is
extremely slow. On average a proton will
wait 10 billion years before undergoing
fusion. Indeed, the only reason the
proton proton reaction proceeds at all
is because there are a heck of a lot of
protons in the sun, allowing it to
convert 600 million tons of hydrogen to
596
tons of helium every second. This sounds
like a lot, but it's actually only a
tiny fraction of the hydrogen available
for fusion. Now stopping for a moment to
look at the big picture. This is very
good news for us earthlings. It means
instead of annihilating itself in a
giant thermonuclear explosion, the sun
has been gently burning through its
hydrogen stocks for around 4.6 billion
years and will continue to do so for at
least a few billion more. It's only
because protons are so slow at
converting into detium that we are here
at all.
For fusion on earth on the other hand,
it is bad news. It means the probability
of proton proton reactions happening
where we have much less plasma and much
less time is essentially zero. Indeed,
the reaction has never been
experimentally measured. In fact,
looking at the problem in the most basic
and fundamental way, it is statistically
impossible to achieve proton proton
fusion on Earth in any meaningful way.
So, what are all these fusion
researchers doing? Why do we even bother
trying? Well, they are not attempting to
fuse protons. Instead, they are trying
to fuse alternative combinations of
nuclei that are much more reactive.
Back in the 1930s, Mark Olphant, a
student of Ernest Brotherford, conducted
a series of experiments. He fired
dutyium nuclei at one another,
generating other exotic hydrogen and
helium isotopes and thus proving that
heavy hydrogen nuclei could be made to
react with one another. Today, fusion
scientists favor a combination that was
first put to use in the H bomb, one that
is 24 orders of magnitude more reactive
than protons alone. It is dutyium.
Remember this is classic heavy hydrogen
consisting of one proton and one neutron
and tritium the even heavier isotope of
hydrogen with one proton and two
neutrons in its nucleus. The reason this
combination is so much more reactive is
that these extra neutrons lead to a
greater strong force and there is no
need for one proton to undergo weak
force mediated beta decay into a
neutron.
Now, dutarium and tritium aren't just
more reactive than the protons that
power the sun. They also give rise to
different reaction products. Instead of
generating an alpha particle and two
protons, they make an alpha particle and
a neutron. But like the proton proton
reaction chain, they still produce a ton
of energy. Energy that we can use to
generate electricity. Just one gram of
detium tritium fuel holds energy
equivalent to 2,400
gallons of oil.
So, if we've identified more reactive
starting materials that give us plenty
of energy out, what's the problem now?
Well, it's not one problem, but
problems. Let's start with those
neutrons.
Being lighter than alpha particles, they
carry most of the energy of the fusion
reaction and so have to be captured in
order for their energy to be put to use.
But controlling a subatomic particle
with no charge is no mean feat. Neutrons
aren't affected by the powerful magnetic
fields containing the plasma and so
stream out of the reactor in all
directions at 16 the speed of light. To
deal with this, most reactor designs
utilize something called a blanket, a
layer surrounding the reaction chamber
that's designed to absorb high energy
neutrons and heat up. This heat can then
be used to generate steam, drive a
turbine, and generate electricity. But
this approach is far from perfect.
Neutrons aren't just absorbed by the
blanket. They ping about everywhere,
damaging everything they hit. This
hugely limits the lifespan of many
components, particularly the reactor
walls. Another issue stems from the
reactants themselves. While dutarium is
relatively common, being easily
extracted from seawater and cheap at $13
a gram, tritium is neither. It has a
halflife of just 12.3 years. And the
only commercial source are Canada's 19
deterium uranium nuclear reactors which
produce just half a kilogram of tritium
a year as a waste product. Now it
estimates that a commercial fusion plant
would require around 125 kg of tritium a
year to run. Current global tritium
reserves are around 25 kg. And as half
of Canada's reactors are due to be
decommissioned this decade, this tiny
reserve is quite literally going to
decay away. But of course, scientists do
have a solution up their sleeves for the
tritium supply problem. As well as
carrying energy out of the reactor,
those high energy neutrons produced by
dutarium tritium fusion can be used for
something called tritium breeding. The
idea is that you make the blanket
surrounding the reactor out of a
substance that generates tritium when
bombarded by neutrons. The substance
preferred by most fusion researchers is
lithium, which upon absorbing a neutron
helpfully decays into a helium atom and
tritium.
However, as ever in fusion, this
solution comes with its own problem. If
each dutyium tritium fusion reaction
generates one neutron, which via lithium
can be used to generate one neutitium,
you would need to operate at an
impossible 100% efficiency to prevent
your tritium supply from dwindling. The
answer most fusion researchers favor is
to add layers of other elements like
burillium that can act as neutron
multipliers, absorbing one neutron and
spitting out two.
But not only is burillium toxic, it is
also in short supply and contaminated
with uranium which then bombarded with
neutrons leads to radioactive byproducts
less than ideal. And regardless, there
are concerns that even with breeding,
most reactors would struggle to generate
enough tritium to be viable.
So, at this point, you might be
thinking, "Hang on a minute. It seems a
lot of the touted advantages of fusion,
bountiful energy, plentiful starting
materials, innocuous, if even useful
byproducts, are kind of falling away."
Well, you'd be right. We're not fusing
hydrogen, or at least the same isotopes
of hydrogen that a star fuses. And we're
not making just helium, but a bunch of
other radioactive products as well. The
simple truth, no matter what the
headlines say, is that we can't make a
star on Earth. And the shortcuts to
create something approximating one,
create a world of engineering
challenges. This is why since the first
fusion reactor patent was granted in
1946,
fusion has always seemed just out of
reach. Each solution comes with a new
set of problems.
But not all hope is lost. In recent
years, things do seem to be changing
with some hugely significant science
breakthroughs. In December 2022, for the
first time ever, more energy was
obtained from a fusion reaction than was
required to initiate it. A challenge
that had eluded researchers for decades.
At the National Ignition Facility, a
research scale ICF reactor in the US,
3.15 megajou of energy was obtained from
a tiny pallet of DT fuel using an energy
input of 2.05 megajou.
Then in late 2023, the experimental jet
reactor in the UK, a TKO, generated a
world record 69 megajou of energy from
just 0.2 mg of DT fuel. And while
international bermas like it inch closer
to operation, a flurry of private
investment has also entered the field
exploring alternative fusion
technologies. One is the
Massachusetts-based Commonwealth Fusion
Systems backed by Google, Nvidia, and
Bill Gates. It proposes using high
temperature superconducting magnets to
produce a more compact TOK. CFS claims
it will have a commercial plant online
by the early 2030s.
Another outfit based out of Washington
State, Helion, believes it is going to
get there even earlier. Backed by the
likes of Sam Alman, this company has
taken a completely new approach to
reactor design. It fires two rings of
plasma together at a million km/h to
generate fusion conditions, a sort of
halfway house between magnetic and
inertial confinement. This approach
allows them to react dutyium not with
tritium, but a reactive isotope of
helium, helium 3, doing away with the
problematic tritium entirely.
The use of helium 3 is key to helium's
approach because instead of producing an
alpha particle and a neutron, these
reactants generate an alpha particle and
a proton. Vitally, this means there is
no neutral particle whizzing off out of
the reactor carrying all the energy.
Energy is retained within the plasma
itself. As the reaction proceeds, the
energy generates an increase in internal
pressure and a change in magnetic field,
which can be used to generate
electricity directly. No Victorian steam
turbines involved at all. So, what's the
catch, you might rightfully ask? Well,
just like tritium, helium 3 is
incredibly rare and also has to be bred
this time from dutyium dutyium reaction.
And this process does generate those
pesky reactor damaging neutrons. One of
Helium's proposed solutions is to
separate the two reactions, having
commercial plants that will use detium
helium 3 and feeder reactors
specifically for generating helium 3
that have planned shorter lifespans.
But there is another issue with detium
helium 3. This mixture requires much
higher temperatures and fuel densities
than conventional detium tritium fuel.
Huge pulses of electricity are needed
each time the reactor fires to generate
fusion conditions, which puts immense
strain on electricity supplies and
reactor components. It's a considerable
engineering hurdle for Helium to
overcome as the company embarks on
building its first commercial scale
reactor, but CEO David Curtley claims
this plant will be online and supplying
power to Microsoft data centers by 2028.
Now, whether or not this comes to pass,
only time will tell. However, even if
none of these private ventures hit their
well publicized milestones, the fact
that this investment exists at all
reflects the moment the fusion sector
finds itself in new algorithmic and AI
tools now at their disposal. For many in
the field, it does feel like Fusion is
finally inching closer to reality. And
though unsolved scientific and
engineering problems exist, regardless
of the approach used, the diversity of
fusion technologies that now exist is a
huge bonus. So while we'll never be able
to recreate a star on Earth, it is very
possible that the one or even several of
the approximations we are trying to
build will play a pivotal role in the
energy landscape of the future.
I'll end by returning to Edington and
his 1920 musings on the energy powering
stars. A star is drawing on some vast
reservoir of energy by means unknown to
us. This reservoir can scarcely be other
than the subatomic energy which it is
known exists abundantly in all matter.
We sometimes dream that man will one day
learn how to release it and use it for
his service. The store is well night
inexhaustible.
If only it can be tapped. Maybe finally
it won't be another 30 years until we
find out if it can.
watching from the sidelines, now is the
perfect time to join the community.