1. 1
ITER
B.Williams*
School of Physics and Astronomy, University of Southampton, UK
Abstract
The International Thermonuclear Experimental Reactor (ITER) is a next generation tokamak fusion
device currently under construction in France. Upon its completion, ITER hopes to break many
fusion records and with its record-breaking budget (in fusion research) there is a lot riding on the
successful operation of the largest tokamak ever designed. Currently there are many scientific
papers on specific parts of ITER, however there is an absence of papers which collate this
information. This paper aims to describe ITER’s history, purpose, design and legacy with particular
consideration to ITER’s prospects for fusion power.
Fusion history and definition
First envisioned in the 1950s, fusion power has been hailed as a cheap, clean and almost limitless
power source that will end our dependence on fossil fuels [1].
Nuclear fusion is a nuclear reaction which releases large amounts of energy when atomic nuclei
combine to form a heavier nucleus. Nuclei naturally repel each other as they are both positively
charged, this repulsion can only be overcome if the reacting nuclei have very high kinetic energies,
achieved by heating the nuclei to ignition temperatures (around 150 million degrees) [2].
Several different fusion processes have powered stars for billions of years.These processes must differ
slightly to be viable on Earth, due to the long timescale of star-based fusion reactions (millions of
years). Terrestrial fusion experiments generally use Deuterium (Hydrogen-2) and Tritium (Hydrogen-
3) as the reactants for fusion because the reaction proceeds more rapidly at a lower temperature than
protonic fusion [3].
The main issues to achieving terrestrial fusion have been the heating of the reactants to fusion
temperatures and confining the plasma (gas of highly ionised particles) long enough for fusion to occur
[1]. Self-sustaining fusion also requires a fusion energy gain factor of infinity (for an ignited plasma),
fusion gain (Q) being the ratio of fusion power to supplementary heating power [3].
Magnetic confinement is the most popular method of confining the plasma to achieve fusion. It uses
magnetic fields to hold the plasma inside a containment vessel and maintain temperatures of
1.5x108
K. The aim being to prevent the particles from touching the reactor walls which would
introduce impurities to the plasma [4].
However these experimental fusion technologies still have a long way to go before commercial fusion
power station’s become an attainable target.
*
Presenting author: Ben Williams, email: bw11g11@soton.ac.uk
𝐇 + 𝐇𝟏
𝟑
→ 𝐇𝐞𝟐
𝟒
+ 𝐧𝟎
𝟏
+ 𝟏𝟕. 𝟓𝟗𝐌𝐞𝐕𝟏
𝟐
Figure 2: Deuterium-Tritium Fusion Reaction [4]
𝑯𝟏
𝟏
+ 𝑯𝟏
𝟏
→ 𝑯𝟏
𝟐
+ 𝒆 𝟏
𝟎
+ 𝝂 𝟎
𝟎
(twice)
𝑯𝟏
𝟏
+ 𝑯𝟏
𝟐
→ 𝑯𝒆𝟐
𝟑
+ 𝜸 𝟎
𝟎
(twice)
𝑯𝒆𝟐
𝟑
+ 𝑯𝒆𝟐
𝟑
→ 𝑯𝒆𝟐
𝟒
+ 𝟐 𝑯𝟏
𝟏
Figure 1: Proton-Proton Chain [27]

2. 2
History of ITER
A tokamak is the favoured design of fusion device utilizing the magnetic confinement method. The
basic design is a doughnut shaped vessel (torus), in which charged particles in the plasma are insulated
from the surrounding walls by a magnetic field. Unlike previous fusion designs the tokamak uses less
energy in the Plasma current and more in the stabilizing magnets leading to considerable
improvements in stability [2].
ITER was first conceived in 1985 by the International Atomic Energy Agency, an “intergovernmental
forum for scientific and technical co-operation in the nuclear field” formed by a collaboration of
nations (Soviet Union, Europe, Japan and the USA) [5].
Conceptual Design of ITER began in April 1988 and incorporated the latest technology of the time. It
was agreed by all the nations that ITER would employ superconducting magnets, to overcome
confinement issues that effected conventional tokamaks (without superconducting magnets);
advanced heating techniques, to improve the efficiency of plasma heating; and also perform fusion
reactions with Deuterium and Tritium. Originally an estimate of $5 billion for construction was
proposed. However by 1995 the price had almost doubled which cumulated in the US government
pulling its financial support in 1998 after researchers at the University of Texas made cynical
expectations about ITER’s performance [6].
However with a redesign and reduction in size and cost, the US reinstated their backing in 2003 and
ITER looked set to begin construction within the next few years [6]. But again arguments erupted over
where ITER was to be constructed, France and Japan were the main contenders each offering to
increase their financial contributions both nations seemingly unwilling to back down. In mid-2005,
Cadarache in Southern France was decided as the ITER site, whilst the Japanese site will be home to a
research centre for testing advanced materials used in the construction of ITER [7].
Aims
The ITER council set forward several guidelines, objectives and performance specifications in June
1998, these aims can be split into four separate categories. The data below comes from the ITER Final
Design Report, Cost Review and Safety Analysis 1998, ITER council Proc.[8].
Plasma performance:
 Achieve a Q≥10 for an extended duration
 Achieve a Q≥5 for steady-state operation
 Research the possibility of controlled ignition
Engineering performance and testing:
 Demonstrate essential fusion reactor technologies working together
 Test the different components of ITER, i.e. blanket, divertor etc.
 Test and evaluate Tritium Breeding Modules (TBM) and also the extraction of neutron energy
and conversion to electrical energy
Design requirements:
 For-fill the performance requirements using engineering technologies from the R&D database
for ITER
 ITER’s parameters must be in agreement with the ITER council’s design rules
 Be able to optimize plasma performance and utilize advanced plasma operation modes

3. 3
 Provide a plasma burn of 300-500s
 Limit operations to ≈10000 pulses
 Testing components under high temperatures and high neutron activity
 To be able to install a TBM at a later unspecified date and therefore allow for the removal of
the original blanket
 Achieving the design at the highest specification at minimal cost
Operation requirements:
 Conduct experiments addressing confinement, exhaust control (impurities and helium) and
stability of the plasma
 Testing blankets for use in next generation fusion reactors and an eventual commercial fusion
power stations
 ITER should have an operational duration of at least 20 years, and so a steady supply of Tritium
for the period is also required
Design
The tokamak design has been around since the late 1950s [3], the ITER design will be the culmination
of over 50 years of tokamak research.
Magnet System
Arguably the most important component of ITER is the magnet system which confines, shapes and
controls the plasma[9]. Unlike JET, ITER utilities superconducting magnets to increase the operational
efficiency as copper coils would consume too much electrical power.
The Magnet System is comprised of four different coil types the toroidal field (TF), poloidal field (PF),
central solenoid (CS) and the correction coils (CC).
The TF coils creates a toroidal magnetic field which directs the particles “the long way round” the torus
[3]. 18 niobium-tin (Nb3Sn) magnets, the largest components of the ITER machine, produce a total
magnetic energy of around 40GJ, a maximum magnetic field of 11.8T and a current of 68kA. The TF
coils are enclosed in strong circular stainless steel cases and also support the PF coils[10].
The PF coils generate a poloidal magnetic field from a toroidally flowing current in the plasma. The
plasma current is induced from a toroidal electric field created by the CS [11]. There are 6 PF coils
comprised of niobium-titanium (NbTi) which sit outside the TF coils and 6 modules of the CS comprised
of niobium-tin. The PF coils use a different material to the TF coils since the maximum poloidal field
value is lower than 6T. Together these coils will be capable of producing “30000 inductively driven
15MA plasma pulses with a burn of about 400s.” [12]
Due to imperfections in magnetic field symmetry created from imperfect positioning of the TF, PF and
CS coils, correction coils are used to counteract these inhomogeneities. To do this “3 sets of 6 saddle
coils are placed around the torus between the PF and TF coils”, these coils provide a small helical field
which stabilises the magnet modes of the total magnetic field[13].
Cooling
Keeping the magnet system cool is a great concern for ITER designers as overheating magnets will
cause instability in the magnetic field and damage to the superconducting magnets. The magnets are
therefore cooled with supercritical Helium (at 4.5K). This temperature cools the magnets sufficiently
to allow the TF and CS coils to operate at 12-13T and the PF coils at 6T. A heat exchanger can also

4. 4
reduce to temperature by another 0.4K which provides the ability to correct any faults discovered
while the magnets are in operation[12].
Heating the Plasma
ITER will have three ways of heating the plasma to fusion temperatures, these sources of external
heating will work together providing an overall heating power of 50MW. Once however “plasma
burning” (self-sustaining fusion) is achieved, external heating can be significantly reduced or possibly
switched off altogether[14].
The first method is Neutral Beam Injection, this involves the injection of high energy particles directly
into the plasma. The particles collide with plasma ions and transfer their energy, heating the plasma.
The beam of particles must be neutral as a beam of ions would not be able to penetrate the magnetic
field, however the actual process uses an ion accelerator and therefore accelerated ions pass through
a gas prior to injection where they recover their missing electron and can be injected into the plasma
as fast neutral atoms[15].
Ions have charge and spin and will travel around magnetic field lines if magnetically confined in a
plasma. This travelling/rotation will happen at a specific frequency (40-55MHz), the Cyclotron
Resonant frequency, and if an electromagnetic wave, of identical frequency, is fired into the plasma
the particles will absorb the wave’s kinetic energy [16]. This method of heating is known as Ion
Cyclotron Resonant Heating.
The third method of heating is through Electron Cyclotron Heating. As stated in the name this method
entails the heating of “electrons in the plasma with a high-intensity beam of electromagnetic radiation
at a frequency of 170GHz.”[14] Because the magnetic field decreases with distance from the tokamak
major axis, the beam of electromagnetic radiation can be directed at a very small region in the plasma
[16].
Vacuum Vessel
The vacuum vessel will house the fusion reactions, it is a double-walled steel torus, where the charged
particles will be magnetically confined without touching the vessel walls. Within the vacuum vessel
are a number of internal, replaceable components, these components will be subject to extreme
neutron radiation and heat. To dissipate some of the heat there are passages within the vessel for
cooling water to pass through[9][17].
Blanket
Covering the interior surface of the vacuum vessel, the blanket is one of the most important and
“technically challenging” components of ITER. Its primary function is to shield the vessel and magnets
from excessive heat and neutron damage, however it must also convert the neutron energy to heat
energy and siphon it off to drive a turbine which will create electrical power [17]. Another crucial job
the blanket has is breeding Tritium. Tritium is very rare as it decays with a half-life of 12.6 years to
Helium-3[18]. There are two types of Tritium Breeder Module (TBM), the solid and liquid variety [19].
Both concepts take neutrons generated from initial fusion reactions to react with Lithium-6, within
the blanket, creating Helium, Tritium and energy (Figure 3); the Tritium is then extracted and re-
injected into the plasma [1]. The Solid TBM uses Li2TiO3/Li4SiO4-Be as the Tritium breeder and the
Liquid TBM uses Pb-15.7Li. Regardless of which blanket design is ultimately chosen it must be able to
operate efficiently, at high temperatures, under constant neutron bombardment, for an extended
duration[4].

5. 5
Divertor
In the Deuterium-Tritium fusion reaction that ITER will eventually experiment with, Helium is created
(Figure 2). This waste must be extracted along with any impurities that may have been introduced to
the plasma during operation. The divertor is found at the bottom of the vacuum vessel and controls
the extraction of unwanted materials from the reactor. Because of its job, the divertor has a high level
of interaction with plasma and consequently must be able to withstand very high surface
temperatures (≥3000K). At present time ITER will test two divertor materials carbon composite (CFC)
and CFC with tungsten targets, the former boasts high thermal conductivity while the latter has a
lower erosion rate (which leads to a longer lifetime) [17].
The poloidal magnetic coils can be used to generate an X-point configuration (Figure 4) which prevents
the plasma from colliding with the reactor walls. Any particles that travel through the edge
(“separatrix”) are directed towards the divertor targets [3].
Bootstrap current
The particles in the plasma travel around the magnetic field lines in tight “gyro-orbits.” However, due
to the irregularity of the magnetic field, the particles drift, tracing out unbalanced (banana-shaped)
orbits. Particle orbits nearer the plasma core create a current through collisions with other particles
and which is transferred into a helical “bootstrap” current [3].The bootstrap current must be greater
than the current created by the solenoid for economic viability. To achieve this requires the reduction
of the turbulent eddies inside the plasma, which will “transport particles and heat outwards across
magnet surfaces.” [3]
Figure 3: Tritium breeding reactions [19]
Figure 4: The X-point and particle orbits [3]

6. 6
Fuelling system/Fuel cycle
ITER will be fuelled in two different ways, the first is utilized when starting up the fusion reaction. After
the air and impurities have been removed from the vacuum vessel and the magnets have been
activated, a gas injection system fires low-density gaseous fuel into the vessel. Once a plasma has been
established, by using an electrical current to ionise the gas fuel particles, a second fuelling system is
triggered. This system is designed to inject solid fuel pellets (small deuterium-tritium ice pellets) at
great velocities (up to 3600km/h) deep into the plasma core. The second fuelling system is used to
control plasma density and “energetic bursts that escape the magnetic field and cause loss of energy”
[17][9].
ITER Buildings
When completed the ITER site will house 39 separate buildings (Figure 5), at the very centre is the
Tokamak Building which will contain the ITER tokamak and also employ many features to ensure the
smooth and safe operation of the world’s largest fusion experiment [20].
Some of the features unique to the Tokamak building include [9]:
 A borated concrete structure around the cryostat of the tokamak which serves as a biological
shield and limits the radiation emitted
 As a further precaution another concrete structure will encase the neutral beam injectors and
the water cooling system acting as an additional confinement barrier
 To contain an accidental release of Tritium a differential pressure is maintained in the different
zones around the tokamak which will stop the spread of Tritium gas as each zone is capable
of detritiation and filtration
Figure 5: The ITER site [20]

7. 7
Schedule for construction
Construction for ITER began in early 2007 with the clearing and levelling of the 42 hectare site in France
(completed late 2010). In August 2011 work began on the foundations for ITER’s Tokamak building
(Seismic Pit basemat) requiring around 110000m3
(roughly 100000 tonnes) of concrete and 3400
tonnes of steel [21]. A deadline of 45 months (from the start of the construction work) for the
construction of the tokamak building complex has been set, this is to allow for the smooth start of the
tokamak assembly [9].
Some of the main components for the tokamak will be manufactured in different member state
countries. The largest of these components will be delivered to a nearby port and transported along
a specially adapted 100km road (modified in 2008-2010 to cope with the size and weight of the
components), the first component is scheduled for delivery in 2014. After all the components have
been delivered it has been estimated that at least 6 years will be required for assembly, testing and
commissioning of ITER [22].
Schedule for operation
Once completed ITER will spend its first 4 years experimenting with Hydrogen and Deuterium fuels
before moving on and using Deuterium-Tritium reactions. Because of this ITER will be operated in 3
successive phases [13].
H Phase: The non-nuclear phase in which only hydrogen and helium plasmas are created, this phase
is mainly for the commissioning, adjustment and optimisation of the tokamak system. The
length of this phase will depend mainly on “the ability to achieve good H-mode
confinement with a suitably high plasma density.” [9]
Figure 6: ITER’s construction schedule [9]

8. 8
D Phase: This phase is used to test, observe and clarify major characteristics of plasma-wall
interactions, these tests will also provide useful information for the D-T phase because of
the similar characteristics between deuterium plasma and DT plasma [23]. Also small
amounts of Tritium are created through these reactions, therefore during this phase
Tritium retention and removal can be explored and tested [24].
DT Phase: The first round of Deuterium-Tritium reactions will involve optimising and increasing tritium
fuelling, fusion power and burn plasma length [13]. The second part of this phase will be
devoted mainly to accomplishment of ITER’s aims and performance requirements (from
the ITER’s aims section), with the final task being the testing TBMs and to assess the overall
achievability of terrestrial fusion [9].
Figure 7: ITER’s operational schedule [13]
Figure 8: Progress towards commercial fusion power plants [5]

9. 9
Conclusion
ITER’s main aim is to prove whether fusion is achievable, it will not however prove the commercial
viability of fusion. If ITER is successful the next step will be DEMO, a demonstration power plant, which
will aim to show that fusion power is efficient and cost effective. ITER will play a big part in the
development of DEMO (Figure 8), particularly in developing radiation-resilient materials. Also, if ITER
is successful during its D-T phase and achieves fusion of several hundred Megawatts for numerous
minutes then the plasma is said to have been ignited, which is a fusion gain (Q) of infinity [3]. This will
be a major breakthrough in fusion exploration and will mark the end of fifty years of struggling to
attain self-sustaining fusion and mark the beginning of the refinement of fusion technology so it can
be utilized in everyday life.
22 years after ITER was first imagined (1985) work began on the ITER site with an estimated
completion date of 2020 and a budget cost of $20 billion. Nevertheless, even as construction is
underway, opposition to ITER is building. The main opposition is in Europe, which is providing around
45% of ITER’s construction cost, “fear that the money will come at the expense of such renewables as
wind and solar.” [25] Whether these fears are substantiated, fusion still remains the best hope for
reducing our dependence on fossil fuels [22].
References
[1] M. Moyer, "Fusion False Dawn," Scientific American, vol. 302, no. 3, pp. 50-57, Mar 2010.
[2] World Nuclear Association, "Nuclear Fusion Power," October 2013. [Online]. Available:
http://www.world-nuclear.org/info/Current-and-Future-Generation/Nuclear-Fusion-Power/.
[Accessed 20 October 2013].
[3] R. Pitts, R. Buttery and S. Pinches, "Fusion: the way ahead," Physics World, vol. 19, no. 3, pp.
20-26, Mar 2006.
[4] S. Cowley, "Hot Fusion," Physics World, vol. 23, no. 10, pp. 46-51, October 2010.
[5] K. Ikeda, "ITER on the road to fusion energy," Nuclear Fusion, vol. 50, no. 1, 1 January 2010.
[6] K. Schneider, "Dream machine," New Scientist, vol. 188, no. 2525, pp. 52-55, 11 November
2005.
[7] D. Clery, D. Normile, G. Yidong and A. Allakherdov, "ITER Finds a Home - With a Whopping
Mortgage," SCIENCE, vol. 309, no. 5731, pp. 28-29, 1 July 2005.
[8] ITER Documentation Series No 15 , "ITER Final Design Report, Cost Review and Safety
Analysis," ITER Council Proc, Vienna, 1998.
[9] "Summary of the ITER Final Design Report," ITER EDA Documentation Series 22, 2001.
[10] "ITER's magnet system," ITER Organization, 2013. [Online]. Available:
http://www.iter.org/mach/magnets. [Accessed 25 October 2013].

10. 10
[11] H. Takatsu, "ITER project and fusion technology," Nuclear Fusion, vol. 51, 31 August 2011.
[12] N. Mitchell, A. Devred, P. Libeyre, B. Lim and F. Savary, "The ITER Magnets: Design and
Construction Status," IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, vol. 22,
no. 3, June 2012.
[13] R. Aymar, P. Barabaschi and Y. Shimomura, "The ITER design," Plasma Physics and
Controlled Fusion, vol. 44, no. 5, pp. 519-565, 22 April 2002.
[14] "External heating systems," ITER Organization, 2013. [Online]. Available:
http://www.iter.org/mach/heating. [Accessed 15 November 2013].
[15] "Tokamak Heating," EDFA, 2013. [Online]. Available: https://www.efda.org/fusion/fusion-
machine/heating/. [Accessed 1 November 2013].
[16] "Ion Cyclotron Resonant Heating," EFDA, 2013. [Online]. Available:
http://www.efda.org/fusion/focus-on/plasma-heating-current-drive/ion-cyclotron-resonant-
heating/. [Accessed 10 November 2013].
[17] "ITER: The Machine," ITER Organization, 2013. [Online]. Available:
http://www.iter.org/mach. [Accessed 25 October 2013].
[18] G. L. Kulcinski and J. F. Santarius, "New opportunities for fusion in the 21st century -
Advanced fuels," Fusion Technology, vol. 39, no. 2, pp. 480-485, March 2001.
[19] Y. Poitevin, "The Tritium breeding blankets for fusion reactors, A key component for
sustainability of fusion energy," in Swiss Nuclear Forum, 2011.
[20] "Buildings and Layout," ITER Organization, 2013. [Online]. Available:
http://www.iter.org/construction/layout. [Accessed 13 November 2013].
[21] D. Shukman, "'Critical phase' for Iter fusion dream," BBC, 7 August 2013. [Online]. Available:
http://www.bbc.co.uk/news/science-environment-23408073. [Accessed 27 November 2013].
[22] S. Connor, "One giant leap for mankind," The Independent, 27 April 2013. [Online]. Available:
http://www.independent.co.uk/news/science/one-giant-leap-for-mankind-13bn-iter-project-
makes-breakthrough-in-the-quest-for-nuclear-fusion-a-solution-to-climate-change-and-an-age-
of-clean-cheap-energy-8590480.html. [Accessed 28 October 2013].
[23] M. Shimada, Writer, Potential ITER plasma operation plan in the H and DT phases.
[Performance]. ITER International Team, 2004.
[24] V. Chuyanov, Writer, Operational plan and Selection of Plasma Facing Components for ITER.
[Performance]. ITPA Garching, 2007.
[25] G. Brumfiel, "Fusion's Missing Pieces," Scientific American, vol. 306, no. 6, pp. 56-61, June
2012.
[26] R. Pogge, "Lecture 13: Energy Generation & Transport in Stars," [Online]. Available:
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/energy.html. [Accessed 26 October
2013].