Session C8
Paper #191
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ITER NUCLEAR FUSION REACTOR: TESTING THE VIABILITY OF FUTURE
FUSION REACTORS
Samuel Schiller, [email protected], Mena 3:00, Daniel Funari, [email protected], Mena 3:00
Abstract—The
ITER
(International
Thermonuclear
Experimental Reactor) is the largest Tokamak nuclear fusion
reactor. Currently under construction in southern France, the
ITER will bring nuclear fusion one step closer to a viable
source of energy. Today, 85% of the world’s energy is
provided by fossil fuels. While effective at producing and
storing large amounts of energy when compared to solar,
wind, and hydroelectric power, the environmental impact of
fossil fuels is highly detrimental. The need for an extremely
efficient, reliable, and environmentally safe source of energy
has never been a more crucial topic. The potential for fusion
power to solve or alleviate the energy crisis is what makes it
so attractive to scientists and engineers alike. However, the
current state of fusion technology is not without its problems,
both scientific and political. ITER may prove to be the next
step in the world of fusion, if it can overcome the issues that
have plagued Tokamak fusion reactors in the past. The
science behind fission and fusion reactions are explained,
including the plasma physics and magnetism behind
Tokamaks, as well as what makes the ITER tokamak different
than reactors past and what the success of ITER could mean
for the world.
commercial style reactor as heat generated from the reaction
will not be used to make steam and will therefore produce no
usable energy. The purpose is instead to allow scientists to
experiment with much higher plasma volumes, in conditions
closer to future commercial fusion power plants [1]. The
hopeful success of the ITER project will break new ground in
implementing a safe, efficient, sustainable, and
environmentally friendly energy source to supply the needs of
the future.
THE SCIENCE OF NUCLEAR ENERGY
Nuclear energy is founded on the immense energy that
is stored in the mass of nuclei. Nuclear fusion is a way to
harness that energy, just as we do today with nuclear fission
power plants and nuclear weapons. As of 2015, Nuclear
fission power makes up about 9% of the United States total
energy production (19% commercial), whereas the remaining
majority of energy of production is from fossil fuels [2].
While fission power does not produce any CO2 emissions, it
does produce radioactive waste, which can be very dangerous
and difficult to dispose of. Each year, about 10,000 m3 of
“high-level waste” is produced by nuclear power plants
worldwide [3], all of which require constant cooling and
shielding due to the heat generated. The spent radioactive fuel
can produce a considerable amount of heat for about 10 years
after use, which must be considered during the disposal
process, as stated by the World Nuclear Association [3].
While not harmful, once the decay heat dissipates to safe
levels, the radioactivity of certain types of the spent fuel take
up to hundreds of thousands of years to fully decay.
Theoretically, the operation of nuclear power plants
should be quite safe, however, there is always the risk of
human error, unpredictable natural disasters, and terrorism,
which can lead to a meltdown. In the case of a meltdown, the
surrounding land will likely become unfit for life for an
extremely long time. For example, the 30 km2 area
surrounding the Chernobyl meltdown will still be dangerously
radioactive for another 20,000 years [4]. Because of these
risks, policy makers remain wary of fission power, despite the
clear advantages.
Keywords—Nuclear Fusion, Tokamak, Renewable Energy,
Nuclear Fission, ITER, Plasma interactions
THE ENERGY CRISIS AND ITER
As climate change continues to become a more
pressing issue, industrialized countries must shift their main
energy focus from fossil fuels like coal, to more
environmentally friendly and sustainable sources. One of
these possible sources is nuclear fusion. Nuclear fusion has
been a sough after energy source since the 1930s when it was
discovered as the source of the Sun’s energy. However, due
to the technical challenges of achieving a controlled and
stable fusion reaction, it has yet to become a viable energy
source.
The International Thermonuclear Experimental
Reactor (ITER) will not only be the largest fusion reactor ever
built, but will be the first to achieve a positive net energy
output. Although ITER will produce more energy than
required to keep it running, it will not function as a
University of Pittsburgh Swanson School of Engineering
3.31.2017
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Samuel Schiller
Daniel Funari
This process is identical to all types of power plants which
instead use the burning of coal or other fossil fuels, which
release harmful amounts of carbon dioxide and other air
pollutants, to create the steam.
Nuclear Fission
Nuclear fission is the splitting of an atomic nuclei. When
a larger unstable atom is split, it will break into 2 smaller
isotopes while emitting some neutrons. However, the sum of
the remaining parts only makes up about 99.9% of the original
mass. The remaining 0.1% is converted into a large amount
of energy conforming to Einstein's mass-energy equivalence
equation E = mc2. The factor c2—the speed of light squared—
is so large, ~9x1016, that even a tiny amount of mass can be
converted to a huge amount of energy. In this case, the energy
required to split the atom is less than the energy released after
fission, resulting in a net energy gain in the form of heat. Just
one atom of enriched uranium — uranium containing a higher
percentage of U-235 isotopes — will release about 200 MeV
(3.2x10-11J) of energy, which on its own is not substantial
since it would take about 3.121 billion of these reactions to
produce 1 joule of heat energy [5]. However, nuclear power
plants use an amount of fuel that far exceeds 3 billion by many
orders of magnitude. The result is a huge amount of energy in
the form of heat. Just one tonne of enriched uranium has the
energy output of up to 20,000 tonnes of black coal or 8.5
million cubic meters of gasoline [6]. Typical power plants use
enriched uranium for fuel, which is 3.5%-5% U-235,
compared to natural uranium that contains only 0.7% U-235
[6]. To start the reaction, alpha particles are fired at neutron
emitting sources (compounds that have beryllium), and a
reaction occurs where a neutron is emitted and a nuclide is
produced. The high-energy neutrons then collide with the
uranium, which is enough to start the fission reaction. Each
U-235 isotope can emit up to 3 neutrons, which proceed to
start more fission reactions, resulting in a prolonged chain
reaction producing immense heat. Much of the U-238 is also
consumed in the reaction and turned into Plutonium which
also undergoes fission, accounting for a third of the reactor's
energy output [6]. The power plant generates electricity, as
seen in the Figure 1, by boiling water from the radioactive
material.
Nuclear Fusion
Nuclear fusion is a process that is very similar to fission,
but it has greater results depending on what nuclei you fuse.
Just as nuclear fission occurs spontaneously yet rarely in
nature, so does fusion. In fact, fusion is occurring all the time,
just not on Earth. The process of nuclear fusion takes place in
the sun (and other stars), and it's what gives the sun its
immense energy. While fission is the splitting of two large
atoms, fusion, is the combination of two lighter atoms, usually
hydrogen and its isotopes (deuterium/tritium). Because of the
massive gravity of the sun, all the hydrogen inside becomes
super compressed and extremely hot — 15 million degrees
Celsius. At this point the hydrogen is no longer gas. The
electrons are stripped from the hydrogen isotopes and plasma,
a fluid of protons and electrons, is formed. The sun then goes
through a process called a proton-proton chain, shown Figure
2, where the immense heat causes two protons to fuse
(overcoming the nuclear and electrostatic repelling force),
one of which will "capture" an electron, thus cancelling out
its charge and creating a neutron.
FIGURE 2 [8]
Proton-Proton Chain
Once fused, the neutron and proton create a deuteron (a
deuterium nucleus). That deuteron will fuse with another
proton (hence the p-p chain term), making Helium-3. Then
two He-3 nuclei will fuse and form unstable beryllium-6,
which degenerates into one Helium-4 nuclei and 2 protons.
Thus 4 protons are transformed into Helium-4. However, the
mass of the resulting Helium nuclei does not equal the mass
of the 4 initial protons. The missing mass, just like in fission,
is converted into heat energy by E=mc2. Just one of these
reactions creates 25 MeV, which is less than the 200 MeV per
Figure 1 [7]
Power Plant Diagram
The steam produced by the boiling water passes through
a turbine connected to an electric generator that converts the
mechanical energy of the spinning turbine into electricity.
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Samuel Schiller
Daniel Funari
U-235 fission reaction. However, per nucleon, fusion
produces about 7 times as much energy than fission
Fission and fusion are opposing processes, and the
reason both release a net heat energy gain, is dependent on
what types of nuclei are being fused/split. If Uranium-235
underwent fusion, there would be a net heat loss, as would
occur if helium underwent fission. This is because the binding
energy of uranium-235 is higher than the sum of the binding
energies of the smaller atoms that would fuse. On the other
hand, the binding energy for helium is lower than the binding
energies of its parts.
The proton-proton chain process described above is the
fusion process in sun and other stars, but unfortunately, that
same reaction cannot be recreated on earth due to the lack of
immense gravitational pressure. In the sun, two protons are
turned into neutrons, a reaction that would take far too long to
complete. To obtain the neutrons, two isotopes of hydrogen,
are used which already contain the necessary neutrons.
Deuterium has one neutron and tritium has two. This D-T
(Deuterium-Tritium) reaction will yield about 17 MeV of
energy, a He-4 particle, and a single neutron (4/5 of that
energy is in the neutron). Then, that neutron is absorbed by a
heat blanket lining the reaction chamber (which is cooled by
water) and converted into electricity via conventional steam
technology. However, since tritium does not occur naturally
in nature, it would have to be bred in the reactor by
bombarding lithium with neutrons.
Nuclear fusion has many benefits over fission. While
uranium is an exhaustible resource, hydrogen is limitless
since it is the most abundant element in the universe. Also,
fission creates radioactive byproducts, while fusion only
produces helium, high energy neutrons which can be easily
contained and present no radiation exposure risk, and tritium
which is recycled and reused in the reactor. There is, in
addition, no risk of a meltdown with fusion, since the reaction
stops when there is insufficient energy. Even if the
containment system fails, the worst that can happen is a fire,
which can be solved by conventional fire safety methods. Yet
while the advantages are clear, fission is a developed
technology that is currently being implemented across the
world. Fusion, on the other hand, is experimental, and while
successful fusion reactions have been created, none have
produced a net heat gain, and these experimental reactors are
only able to function in short bursts [10][11].
Containing 150 Million Degree Plasma
The first and most obvious challenge is the incredibly
high temperatures needed for the fusion reaction to take place.
The fusion of deuterium and tritium requires temperatures
upward of 150 million degrees Celsius [12]. The sun, which
burns at approximately 15 million degrees, is only able to
sustain its fusion due to the immense pressure inside its core.
The approximately 150-million-degree plasma that fusion
requires would instantly vaporize and destroy any surface that
it touched. Scientists overcame this difficulty with the use of
magnetic confinement, which uses a series of magnets to
levitate the plasma inside of the reactor [12]. Even with
magnetic confinement however, the inner walls of current and
future reactors will over time become damaged by the
frequent exposure to the hot plasma. The tiles lining the
reactor walls will need recurrent replacement to ensure no
damage occurs to vital components of the reactor.
Structural Challenges
Current fusion reactors do not operate continuously and
instead function in long pulses. In addition to this intense heat,
the reactor, throughout its lifetime will be subjected to
thousands of these magnetic pulses, putting an extreme
amount of stress onto the structure of the reactor. The
structure must be able to withstand these pulses in
combination with the weakening of the metals caused by the
extreme heat. According to a 2001 journal article about
plasma material interactions (PMIs) from the Institute of
Physics, the energy exposed to the wall, “can be high enough
to melt and vaporize the surface material rapidly” [13].
In addition to the weakening of reactor walls due to heat,
exposure to the plasma has other degrading effects, mainly
erosion and hydrogen trapping. Erosion of the reactor walls is
due to many processes, but mainly by a process called
sputtering [13]. Sputtering occurs when atoms in a material
become energized to the point of overcoming their binding
energy, and are then ejected from the surface. This process
effectively determines the life of the plasma facing
components (PFCs) [13]. The repeated ejection of atoms not
only produces PFC erosion but causes impurities which cool
the plasma core, possibly affecting the fusion reactions. The
plasma also causes an accumulation of hydrogen deposits,
mainly tritium, which also weaken the PFCs. The deposited
tritium must be removed regularly to ensure proper function
and prevent further wall damage and plasma impurity [13].
Having to contain such a high-energy source as fusing plasma
causes immense structural integrity challenges.
CHALLENGES FOR FUSION POWER
Fusion power is the most ideal energy source. It’s able
to create an enormous amount of energy from a limited
amount a fuel, like nuclear fission, while producing no long
lasting radioactive waste or other toxins released into the
environment. Being such an ideal source, it has many
challenges.
Cost and Availability
The most important challenge affecting the rate of
fusion research is development cost. Modern fusion reactors
require billions in funding and can take more than a decade to
construct. The ITER reactor is projected to cost well over $18
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Daniel Funari
billion [14]. Therefore, ITER required funding by multiple
countries to sustain its cost. Although fusion research and
construction requires billions in funding, the low cost of the
electricity it produces “force fusion power towards base-load
supply” [13]. A base load energy source is used continuously
to supply the minimum daily energy needed. A fusion plant
must have very minimal down time to sustain this supply
need, which while easily reached by fission, “will be a stretch
for any planned fusion power station” [13]. The practicality
of sustained energy generation in Tokamak style reactors will
be one of the main question to be answered by the ITER
project.
production accounted for 37% of the total 2015 CO 2
emissions in the US [16]. Under this definition, fusion power
is incredibly sustainable. In research conducted at the
University of Tokyo, early fusion reactors in total would
produce around 43.9g of CO2 for every kWh of energy
produced, with modifications that could lower this value to
only 22.5g for future reactors, which is on par with fission and
hydroelectric power [17]. In addition, fusion produces a much
greater amount of energy compared to these sources.
However, economic sustainability is as much an issue. As
stated previously, fusion reactors require decades of
construction time and billions of dollars in funding, which
makes fusion less economically viable in the near future.
Future reactors would need to be much cheaper than the
ITER. Another important factor is the abundance of fusion
fuel. Hydrogen-1 and deuterium are easily extracted from
water and heavy water and do not pose any supply difficulty.
However, tritium must be produced from lithium. While
reserves contain an abundant supply of lithium, the use of its
us in batteries has been exponentially increasing which could
pose a supply risk for fusion power [18]. From research
conducted at the Max Planck Institute for Plasma Physics,
seawater theoretically contains enough lithium to supply
“2,760 power plants for 23 million years” [18]. Although this
is only theoretically, the scale of this value ensures that
consuming the Earth’s lithium supply is not an issue for
fusion power, especially with the continuing research into
non-lithium batteries. While fusion power is extremely
environmentally friendly, it is still questionable whether it
will be economically sustainable.
Production of Dangerous Materials
The argument for fusion power is that it can produce
power on the scale of fission power without the waste or
possibility of a meltdown. While all radioactive isotopes
involved in the fusion process have short half-lives, ensuring
power plants will not expose damaging amounts of long lived
radioactivity to the surrounding environments, skeptics claim
that dangers may arise in the large-scale adaptation of fusion
energy [15]. The two components of the fusion process that
this danger arises from are tritium, one of the two hydrogen
isotopes fused, and high-energy neutrons. Even though
tritium has many industrial uses, it is radioactive and is also
an essential component in boosted fission weapons which
increase the explosive yield of fission weapons by adding a
small fusion reaction triggered by the fission explosion.
However enriched uranium and other nuclear materials are
needed in addition to the tritium to develop fission boosted
weapons. Should nuclear weapon growth become a more
concerning issue, international restrictions may be placed on
tritium availability, which could dramatically affect nuclear
fusion research. The other concerning product of fusion
reactions is the release of high-energy neutrons [15]. When
these neutrons strike “depleted uranium”, they bind to some
nuclei and transform parts of the uranium into fissile isotopes
that can be used in nuclear weapons. According to a 2008
report by the Institute of Physics on nuclear fusion, a reactor
with this intent would require “special engineering of the
tokamak, including additional cooling, shielding and a
reprocessing capability” [15]. These additional features
would be easily noticed and regulations “should be sufficient
to prevent illicit production of any fissile materials” [15]. This
reprocessing ability however, is beneficial as it creates fuel
for use in fission power plants. Although there are many
safeguards in place to prevent illicit production of fissionable
materials, should fusion energy become widely adopted,
increased regulations and monitoring may be necessary.
TOKAMAK STYLE REACTOR
The most developed reactor design currently is the
tokamak reactor. While tokamaks vary in shapes and sizes,
the general design remains unchanged. A tokamak reactor
contains the plasma by means of a toroidal shaped reaction
chamber. Using magnetic fields, the plasma is able to be
confined and controlled within the torus [10].
Plasma Confinement
For an earth bound fusion reaction to take place, the
deuterium and tritium must be heated to extreme temperatures
of around 150 million degrees Celsius (10 times hotter than
the sun). Once the fuel reaches this temperature, there is then
the problem of containing it. Because proton plasma at 150
million degrees Celsius is completely ionized and is
electrically charged, it can be manipulated by magnetism. The
plasma creates its own magnetic field due to its high volume
of charged particles, and is thus affected by the magnetic field.
This is done with 3 sets of magnetic coils in most cases,
sometimes with 4. Around the torus, there are several vertical
coils called the toroidal coils that induce a current in the
plasma which goes around in a circle (following the path of
the doughnut-shaped chamber). Also around the torus, there
Economic and Environmental Impact
When discussing the sustainability of a certain
technology, people mainly think about its environmental
impact. This is understandable considering that energy
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Daniel Funari
are a series of horizontal coils that surround the reaction
chamber [10]. These coils, called the poloidal coils, induce a
current in the plasma that goes in circles perpendicular to the
toroidal induced current. Along with the poloidal coils shown
in Figure 3, there is also a central solenoid coil that induces a
field like that of the poloidal coils [10].
also increases, which causes even more heat by fusion and
kinetic energy. While higher power magnets induce more
current, they also compress the plasma further, which
increases the collision frequency and plasma pressure, which
in turn increases temperature. There are issues with induced
current plasma fusion however. In order to induce a current,
the reactor must be run by a giant transformer, which
intrinsically operates in a pulsed manner, thus the plasma can
only exist and be contained for short bursts. When the
transformer is recharging, the plasma ceases [19]. The run
time of tokamak reactors could possibly be prolonged by use
of a complex plasma mechanic called the bootstrap current
[20]. Due to the lack of uniformity in the magnetic field, the
motion of the plasma is not symmetrical. This leads to a
residual current that is not induced [20]. This problem can
also be alleviated using other heating methods [15].
One way to heat the plasma is through neutral beam
heating [19]. With this method, beams of neutral particles that
are not affected by the magnetic field are fired into the
plasma/fuel in order to heat it. To accomplish this, isotopes of
hydrogen, deuterium, hydrogen-1, or tritium, are accelerated
through a high voltage, into a neutralizer section (such as a
gas cloud), where they gain electrons to become neutral [19].
Once neutral, the particles still have a high remaining velocity
as they enter the reaction chamber to collide with the plasma,
thus increasing the plasma's overall speed and heat. Another
way is through radio-frequency heating [19]. In this process,
high frequency electromagnetic waves are generated outside
the torus that match the resonance of the particles in the
plasma. The energy in the waves can then be added to the
energy in the plasma, increasing its overall heat. Once fusion
occurs, the heat from the expelled neutrons collides with the
walls of the reactor chamber, which is cooled by water. Then
the fusion part of the process is over and electricity is
generated through conventional steam technology. For a net
energy gain to occur, the heat energy generated must exceed
the energy required start and sustain the reaction.
Unfortunately, no reactor has been able to accomplish this so
far, rendering all current fission reactors purely experimental.
The current largest tokamak reactor is the Joint European
Torus (JET), which has a major radius of 3 meters with a
plasma volume of 100 m3, and was able to generate 16 MW
of power for a few seconds. The JET reactor only produces
about 64% of the 24 MW input energy [21].
Figure 3 [15]
Tokamak Magnet Set-Up
These coils essentially make up a giant transformer, where the
plasma acts as a secondary winding. The result is a helical
shaped current that spins around the in the toroid. This motion
of the plasma keeps it in the center of the chamber cross
sections, away from any chamber walls. In some tokamaks,
there are also helical coils surrounding the chamber, which
assist further in the motion/confinement of the plasma.
Because all the electrons are separated from the protons in the
plasma, there is a two-way motion going on in the torus.
While the positive charges circle one way, the stripped
electrons rotate the other way [15]. The plasma inside the
torus ends ups moving rapidly, with current tokamaks
reaching speeds upward of 100 km/s. These extreme speeds
increase the number of collisions and in turn, the number of
fusion reactions [19].
Plasma Heating
Containing super-heated plasma is just one of the
challenges associated with fusion reactors. Heating the fuel to
the required temperature, and keeping it there, is done in a
combination of many different ways. One way is by
magnetism/ohmic heating, which is also the same process
confining the plasma [10]. When a such a high-energy current
is induced in the fuel/plasma, it increases the amount of
resistance per second the current must go through. This results
in a great amount of induced heat. Unfortunately, as the heat
of the plasma increases, its resistance decreases, thus reducing
the heating effect. The magnetic coils heat the plasma in other
ways as well. Due to the high speeds at which the plasma is
moving from the induced current, the number of collisions
ITER: FIRST ENERGY PRODUCING
FUSION REACTOR
ITER is will be the first reactor that will have a Q-value
above 1. The Q-value is the ratio of output energy to input
energy. With the Q-value estimated to be around 10, ITER
will produce 500 MW of heat from an input of only 50 MW
[1]. The reactor, as the name states, is purely experimental, as
it will not actually generate usable energy from the produced
heat. However, the knowledge of much higher plasma volume
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Daniel Funari
interactions will pave the way for reactors that will.
History and Construction
The ITER project was first proposed in 1985 by the
Soviet Union. The idea was to create an international effort to
develop nuclear fusion as viable energy source. The following
year the United States reached an agreement with the
European Union, Japan, and the Soviet Union to collaborate
on a design for a large international fusion reactor [21]. The
design process began midway through 1988 with the
Conceptual Design Activities (CDA) in Germany which
through 1990, in addition to designing the reactor, performed
an environmental impact analysis, developed site
requirements, estimated the cost, and outlined the schedule
for the engineering, design, and operation [21]. Two years
after the completion of the CDA, the Engineering Design
Activities (ERA) began which carried on through 2001. After
completing the initial design in 1998, the ERA was extended
three years to implement further cost cutting measures.
During this ERA extension period the US withdrew, although
temporarily, due to concerns about the projected cost. In
2005, the ITER members officially agreed to construct ITER
in Cadarache, France. The ITER agreement was signed in
November of 2006 and construction began only two months
later [20]. Construction of the reactor building however, did
not begin until August of 2010.
Initially, during the CDA, the estimated cost and
schedule was laid out. According to the official CDA report,
ITER was estimated to be completed by 2003, with only $4.9
Billion in construction costs [14]. Although this was only an
initial estimation, the cost continually rose. Currently, the
estimated cost is around the scope of $18 Billion. When
construction began in 2010, the ITER schedule planned for
the first plasma operation in 2019, with the first D-T plasma
occurring in 2027. In an ITER Council meeting in November
of last year, the schedule was unanimously delayed again,
projecting initial plasma in 2025, and D-T operation in 2035
[22]. While it is too early to tell if this updated schedule will
hold up, managing members claim ITER has remained on
schedule, and on budget throughout 2016, increasing global
confidence in ITER’s success.
Figure 4 [21]
ITER Size Comparison
ITER is planned to have a 500 MW energy output and a 300500 second run time, compared to JET's output of 16 MW and
run time of 60 seconds. The DEMO reactor, which is also
shown in Figure 4, will be expanded on later and is the
succession to the ITER project. The vacuum vessel where the
reaction takes place will be made from 5200 tonnes of
stainless steel. Lining the wall of the chamber will be the
blanket. The blanket (covering 600 m2) will be responsible for
absorbing most the heat from the plasma. The ITER team has
chosen beryllium as the element to cover the first blanket wall
for its high heat resistant qualities, with stainless steel and
copper as the secondary walls. The blanket will be hit by the
high-energy neutrons from the fusion reaction, absorbing
their heat energy. ITER will be the first reactor to utilize
active water cooling, where water is pumped around the
blanket constantly to remove massive amounts of heat. The
blanket is planned to be made up of 440 modules, each
weighing 4.6 tonnes. ITER will also be the first reactor to be
designed for deuterium and tritium reactions. In the blanket,
there will be 6 dedicated ports that will be open for a lithium
layer that will breed tritium once a high-speed neutron
collides with it. While not fully designed to accommodate
entirely self-sufficient tritium breeding, ITER will be able to
accommodate tritium breeding testing that will give us the
research necessary for future reactors [1].
The magnets that will heat and confine the plasma will
have a stored energy of 51 Gigajoules, and a combined
magnetic field of 30.8 T (Tesla). The magnetic coils are made
of niobium-tin, which is superconductive at 4 degrees Kelvin.
By use of cryogenically cooled helium, the 10000 tonnes of
coil will be cooled to 4 K, thus reducing the power needed to
operate the coils and optimizing the net energy gain from the
reaction. The cryogenic helium will be cooled in a series of
helium refrigerators in a separate building, with a total helium
supply of 25 tonnes.
Niobium-tin is extremely expensive, and ITER
demands 100,000 km of it for the coils, an amount which has
taken 9 suppliers 7 years to manufacture. To put in
perspective, during coil production the 15 tonne/year
production rate increased to 100, just for ITER. Surrounding
What Makes ITER Different
Much of what makes ITER different is simply the scale
at which all the components have been ramped up. ITER
boasts multiple record breaking scientific endeavors, such as
having the some of the largest vacuum systems,
superconducting magnetic coil, and cryogenic systems ever
built. The primary systems alone will weigh 23,000 tonnes.
The ITER tokamak will be the largest Tokamak ever built,
with a chamber radius of 6.2 meters and a plasma volume of
840 m3. As seen in Figure 4 demonstrating ITER’s size, the
planned capabilities of ITER far exceed the current
capabilities
of
any
of
its
predecessors.
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Samuel Schiller
Daniel Funari
the torus, there will be 18 “D”-shaped toroidal magnets, each
weighing 310 tonnes (for a total of 5,580 tonnes). ITER
installed the first of these magnets in January of this year. The
toroidal magnets will store 41 GJ, and generate 11.8 T of
magnetic field. There will also be 6 poloidal magnets, the
largest with a diameter of 24 meters and a weight of 400
tonnes, storing 4 GJ and generating a magnetic field of 6 T.
The largest magnet will be the central solenoid, standing at 13
meters tall and 4 meters wide (1000 tonnes), storing 6.4 GJ
and emitting a field of 13 T. The solenoid will induce a current
of 15 MA in the plasma, making it the backbone of the entire
magnet system. All of these systems will be housed in an
enormous 16,000 m3 vacuum chamber that stands 30 meters
high that will evaporate and prevent any inside moisture
[1][19].
As the plasma develops, fuel will be injected at 400 PA
m3/s, an entire order of magnitude higher than any existing
fuel injecting system. In order to meet the initial heat required
for fusion to occur, ITER will utilize 3 external heating
systems. The first one, two neutral beam injectors, will fire
deuterium isotopes at 4 times the speed of any existing neutral
beam injector. However, this makes using positive ions very
difficult to neutralize prior to entering the reactor. Instead of
using positive ions, ITER will fire negative ions into the
plasma since the extra electron that makes it negative is
loosely bound. Secondly there will be 2 external
electromagnetic wave heaters, one that emits waves at a
frequency resonant to that of the ions, and one that emits
waves with a resonance to that of electrons (170 GHz). The
waves will increase the energy of the ions/electrons, which
will in turn increase the heat of the system [15][19][24].
FUSION’S FUTURE
A world powered by fusion power is not imminent.
There still much more research needed to determine the
viability of nuclear fusion as a source of energy. With the
initial operation of ITER less than ten years away, a world
powered by fusion may be a reality within the century. Should
ITER construction and operation remain on track, multiple
DEMO reactors could then be constructed around the world,
producing gigawatts of clean, sustainable, and inexhaustible
energy, ending the need for environmentally damaging
energy sources like coal, oil, and natural gas.
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After ITER: “DEMO”
Depending on ITER’s success, the next step in the world
of fusion will be the DEMO reactors. DEMO will be the
“demonstration” prototype reactors for the world of
commercial nuclear fusion power. While ITER's purpose is to
demonstrate the safety and possibility of net energy and
tritium breeding, DEMO's purpose will be to demonstrate the
economic efficiency of fusion. While ITER uses tritium
mostly from the global deposit, DEMO will breed 100% of its
tritium on site. Other goals of DEMO include continuous
operation, a Q-value between 30 and 50 compared to ITER’s
Q-value of 10, and a focus on energy collection rather than
diagnostics [24].
While DEMO is far down the road (too early to estimate
its completion date), currently there are other reactor designs
in development alongside ITER, that could also hold promise.
Spherical tokamaks change the way the plasma behaves,
increasing energy output at a lower cost. The stellarator
reactor is a similarly shaped reactor that operates without the
need for an induced plasma current by twisting the plasma,
allowing prolonged periods of operation compared to
tokamaks [20].
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ACKNOWLEDGMENTS
We would like to thank our co-chair, Danielle Broderick, for
continually taking time out of her busy schedule to help us
with this project
ADDITIONAL SOURCES
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8