PHYSICS PROJECT
Ujjwal Kulshreshtha
XI – J
Nuclear Fusion
1
Table of Contents
2
What is Nuclear Fusion?
Nuclear fusion is the process by which two light atomic nuclei
combine to form a single heavier one while releasing massive
amounts of energy.
Fusion reactions take place in a state of matter called plasma — a hot,
charged gas made of positive ions and free-moving electrons with
unique properties distinct from solids, liquids or gases.
The sun, along with all other stars, is powered by this reaction. To
fuse in our sun, nuclei need to collide with each other at extremely
high temperatures, around ten million degrees Celsius. The high
temperature provides them with enough energy to overcome their
mutual electrical repulsion. Once the nuclei come within a very close
range of each other, the attractive nuclear force between them will
outweigh the electrical repulsion and allow them to fuse. For this to
happen, the nuclei must be confined within a small space to increase
the chances of collision. In the sun, the extreme pressure produced by
its immense gravity creates the conditions for fusion.
Why do scientists study nuclear
fusion?
Ever since the theory of nuclear fusion was understood in the 1930s,
scientists — and increasingly also engineers — have been on a quest
to recreate and harness it. That is because if nuclear fusion can be
replicated on earth at an industrial scale, it could provide virtually
limitless clean, safe, and affordable energy to meet the world’s
demand.
3
Fusion could generate four times more energy per kilogram of fuel
than fission (used in nuclear power plants) and nearly four million
times more energy than burning oil or coal.
Most of the fusion reactor concepts under development will use a
mixture of deuterium and tritium — hydrogen atoms that contain
extra neutrons. In theory, with just a few grams of these reactants, it is
possible to produce a terajoule of energy, which is approximately the
energy one person in a developed country needs over sixty years.
Efforts are being made to develop practical fusion reactors, like the
experimental ITER (International Thermonuclear Experimental
Reactor) project, which aims to demonstrate the feasibility of
sustained nuclear fusion reactions and potentially pave the way for
future commercial fusion power plants..
Comparison to nuclear fission
Both fission and fusion are nuclear processes by which atoms are
altered to create energy. Nuclear fission takes place when a large,
somewhat unstable isotope (atoms with the same number of protons
but different number of neutrons) is bombarded by high-speed
particles, usually neutrons. These neutrons are accelerated and then
slammed into the unstable isotope, causing it to fission, or break into
smaller particles. During the process, a neutron is accelerated and
strikes the target nucleus, which in the majority of nuclear power
reactors today is Uranium-235. Fusion takes place when two low-
mass isotopes, typically isotopes of hydrogen, unite under conditions
of extreme pressure and temperature.
4
History of Nuclear Fusion
In 1921, Arthur Eddington suggested hydrogen–helium fusion could
be the primary source of stellar energy. Quantum tunnelling was
discovered by Friedrich Hund in 1927, and shortly afterwards Robert
Atkinson and Fritz Houtermans used the measured masses of light
elements to demonstrate that large amounts of energy could be
released by fusing small nuclei. Building on the early experiments in
artificial nuclear transmutation by Patrick Blackett, laboratory fusion
of hydrogen isotopes was accomplished by Mark Oliphant in 1932. In
the remainder of that decade, the theory of the main cycle of nuclear
fusion in stars was worked out by Hans Bethe. Research into fusion
for military purposes began in the early 1940s as part of
the Manhattan Project. Self-sustaining nuclear fusion was first carried
out on 1 November 1952, in the Ivy Mike hydrogen (thermonuclear)
bomb test.
Sir Arthur Stanley Eddington
- Suggested Hydrogen Helium fusion
could be a primary source of energy
This Photo by Unknown Author is
licensed under CC BY-SA Patrick
Blackett
- Conducted early experiments on
artificial nuclear transmutation
This Photo by Unknown Author is licensed
5 under CC BY-SA
The Ivy Mike Hydrogen bomb
- The first self sustaining
Nuclear fusion was carried out
on 1st November 1952, in the
Ivy Mike Hydrogen Bomb test
While fusion was achieved in the operation of the hydrogen bomb (H-
bomb), the reaction must be controlled and sustained in order for it to
be a useful energy source. Research into developing controlled fusion
inside fusion reactors has been ongoing since the 1930s, but the
technology is still in its developmental phase.
The US National Ignition Facility, which uses laser-driven inertial
confinement fusion, was designed with a goal of break-even fusion;
the first large-scale laser target experiments were performed in June
2009 and ignition experiments began in early 2011. On 13 December
2022, the United States Department of Energy announced that on 5
December 2022, they had successfully accomplished break-even
fusion, "delivering 2.05 megajoules (MJ) of energy to the target,
resulting in 3.15 MJ of fusion energy output
THE FIRST EVER BREAK- EVEN FUSION WAS
ACCOMPLISHED ON 5TH DECEMBER 2022
6
Fundamentals of Nuclear Fusion
ROLE OF DEUTERIUM AND TRITIUM:
Hydrogen isotopes play a crucial role in nuclear fusion, especially in
the context of controlled fusion reactions aimed at producing energy
on Earth. The two primary hydrogen isotopes used in fusion research
are deuterium and tritium.
1. Deuterium (D): Deuterium is an isotope of hydrogen that contains
one proton and one neutron in its nucleus, making it twice as heavy as
regular hydrogen (which only contains one proton). Deuterium is
relatively abundant and can be extracted from water, making it an
attractive fuel source for fusion reactions.
2. Tritium (T): Tritium is another hydrogen isotope that contains one
proton and two neutrons in its nucleus, making it even heavier than
deuterium. Tritium is not naturally abundant and must be produced. It
is radioactive and has a short half-life of about 12 years, meaning it
decays over time. Tritium is used to enhance the fusion process
because it undergoes fusion reactions more easily at lower
temperatures and pressures compared to deuterium-deuterium
reactions.
In the context of nuclear fusion research, the fusion of deuterium and
tritium is the most practical and achievable fusion reaction under
current technology:
7
Deuterium-Deuterium Fusion: This reaction involves two deuterium
nuclei fusing to form a helium nucleus and releasing a high-energy
neutron. While this reaction is possible, it requires extremely high
temperatures and pressures, making it more challenging to achieve the
necessary conditions for sustained fusion on Earth.
Deuterium-Tritium Fusion: This reaction is more efficient in terms
of the conditions required for fusion. When deuterium and tritium
nuclei fuse, they form a helium nucleus, releasing a high-energy
neutron and a substantial amount of energy. Tritium's readiness to
undergo fusion at lower temperatures makes it an important
contributor to achieving self-sustained fusion reactions.
In experimental fusion devices like tokamaks and stellarators,
scientists are working to create the extreme temperatures and
pressures necessary to initiate and sustain deuterium-tritium fusion.
The energy released during this fusion reaction can be harnessed to
generate electricity, potentially providing a clean and virtually
limitless energy source.
It's important to note that while deuterium is abundant and relatively
easy to extract, the need for tritium raises challenges due to its
radioactive nature and short half-life. Methods for tritium production,
storage, and recycling are
critical aspects of
developing practical
fusion reactors.
8
Temperature and Pressure conditions for nuclear
fusion:
Magnetic Confinement Fusion:
In this approach, a high-temperature plasma is confined using strong
magnetic fields to achieve the necessary conditions for fusion. The
key parameter that characterizes the performance of a magnetic
confinement fusion device is the product of plasma density (n) and
confinement time (τ), known as the "fusion triple product" (nτT).
Temperature: The plasma temperature typically needs to be in the
range of tens of millions of degrees Celsius (kelvins) or even higher.
The specific temperature depends on the type of fusion reaction being
pursued, with deuterium (D) and tritium (T) being common fuel
choices.
Pressure: The pressure in the plasma is usually described in terms of
plasma beta (β), which is the ratio of plasma pressure to magnetic
pressure. Achieving the necessary pressure involves both the
temperature and the density of the plasma.
Inertial Confinement Fusion:
In this approach, a small pellet of fusion fuel (often deuterium and
tritium) is rapidly compressed and heated using intense energy from
lasers or other means. The compression generates high pressure and
temperature at the core of the pellet, leading to fusion.
Temperature: The central temperature required for ignition is
typically around 100 million degrees Celsius (kelvins) or higher.
9
Pressure: The pressure required for inertial confinement fusion is
extremely high. The pressure is often measured in giga-pascals (GPa)
or even tera-pascals (TPa), which are millions to billions of times
atmospheric pressure.
Reaction pathways and energy release:
The specific reaction pathways and energy release depend on the
types of nuclei involved in the fusion reactions. Two common fusion
reactions that are of interest for potential energy generation are
deuterium-tritium (D-T) fusion and proton-proton (p-p) fusion.
Deuterium-Tritium (D-T) Fusion:
In the context of nuclear fusion research for energy generation, the
most promising reaction is the fusion of deuterium (D, a heavy
isotope of hydrogen with one proton and one neutron) and tritium (T,
another heavy hydrogen isotope with one proton and two neutrons).
Reaction Pathway:
D + T → He-4 (helium-4) + n (neutron) + energy
Energy Release:
In this reaction, the majority of the released energy comes in the form
of kinetic energy of the helium-4 nucleus and the high-speed neutron
produced. The helium nucleus (alpha particle) carries substantial
kinetic energy due to the high velocities of the reacting particles. The
kinetic energy is then converted into thermal energy through
10
collisions and interactions within the fusion plasma. This thermal
energy can be harnessed to generate electricity through traditional
methods, similar to how it's done in conventional power plants.
Proton-Proton (p-p) Fusion (Solar Fusion):
Proton-proton fusion is the primary process that powers the sun and
other stars. It involves the fusion of protons (hydrogen nuclei) to form
helium nuclei.
Reaction Pathway:
There are several steps in the proton-proton chain,
but the basic reaction can be summarized as:
4 protons → He-4 (helium-4) + 2 positrons + 2
neutrinos + energy
Energy Release:
In this reaction, the released energy primarily takes the form of
gamma-ray photons. These high-energy photons carry away the
energy released during the fusion process. In the sun, these gamma-
ray photons travel outwards and eventually reach the surface, where
they are emitted as sunlight.
11
Current research and development
Overview:
Here's an overview of some of the leading fusion research projects:
ITER (International Thermonuclear Experimental Reactor):
ITER is one of the most ambitious and well-known fusion research
projects. It's an international collaboration involving 35 countries and
is located in Cadarache,
France. ITER aims to
demonstrate the
feasibility of sustained
nuclear fusion reactions
as a practical and
sustainable energy
source.
Approach: ITER uses
This Photo by Unknown Author is licensed under CC BY
the magnetic
confinement fusion approach, specifically the tokamak design. It will
confine a high-temperature plasma of deuterium and tritium using
powerful magnetic fields to achieve the conditions necessary for
fusion.
Goal: ITER's primary goal is to produce 10 times more energy from
fusion reactions than the energy required to sustain the plasma (a
concept known as "ignition" or "breakeven"). It's not intended for
commercial power generation but rather to validate the scientific and
engineering principles of a controlled fusion reaction.
12
Wendelstein 7-X:
Wendelstein 7-X is a large stellarator fusion device located in
Greifswald, Germany. It's operated by the Max Planck Institute for
Plasma Physics (IPP) and is designed to study the potential of the
stellarator concept for magnetic confinement fusion.
Approach: Unlike tokamaks, stellarators use twisted magnetic fields
to confine the plasma without the need for a continuous external
current. This design offers the advantage of steady-state operation,
potentially eliminating some of the instabilities seen in tokamaks.
Goal: Wendelstein 7-X's primary goal is to demonstrate the feasibility
of steady-state plasma operation and confinement in a stellarator
configuration. It aims to provide valuable insights into the viability of
stellarators for future fusion power plants.
National Ignition Facility (NIF):
NIF, located at Lawrence Livermore National Laboratory in the
United States, focuses on inertial confinement fusion (ICF) research.
It uses high-powered lasers to compress and heat small pellets of
fusion fuel, aiming to achieve the conditions required for fusion
ignition.
Approach: NIF's approach involves rapidly compressing a small
fusion fuel pellet using laser-induced shock waves. The resulting high
pressure and temperature can initiate fusion reactions.
13
Goal: NIF's main goal is to achieve ignition, where the energy
produced by the fusion reactions exceeds the energy delivered by the
lasers. While NIF's primary focus is on national security and nuclear
weapons research, its findings are also relevant to controlled fusion
for energy.
SPARC (Smaller, Power-producing Advanced Reactor Concept):
SPARC is an experimental compact tokamak design being developed
by the private company Commonwealth Fusion Systems (CFS) in
collaboration with MIT's Plasma Science and Fusion Center. It aims
to demonstrate net energy gain from fusion.
Approach: SPARC aims to use high-temperature superconducting
magnets and advanced plasma physics to achieve high performance
and energy gain in a smaller and more cost-effective tokamak.
Goal: SPARC's primary goal is to achieve a burning plasma state,
where the energy produced by fusion reactions significantly exceeds
the external input energy. If successful, SPARC could pave the way
for future commercial fusion power plants.
Challenges in achieving controlled fusion:
Achieving controlled nuclear fusion for practical energy generation is
an incredibly challenging endeavor due to the complex interplay of
physical, engineering, and materials science factors. Some of the
major challenges include:
14
High Temperature and Pressure: Fusion reactions require extremely
high temperatures (tens to hundreds of millions of degrees Celsius)
and pressures (millions to billions of times atmospheric pressure) to
overcome the electrostatic repulsion between positively charged
atomic nuclei. Containing and maintaining these extreme conditions
without melting or damaging the containment materials is a
significant challenge.
Plasma Instabilities: The high-energy plasma used in fusion
reactions is prone to instabilities that can disrupt its confinement and
stability. These instabilities, such as plasma turbulence and
disruptions, can lead to energy losses and damage to the plasma-
facing components.
Confinement and Heating: Magnetic or inertial confinement
methods must be used to contain and heat the fusion plasma.
Achieving and sustaining the necessary conditions for fusion while
minimizing energy losses and improving confinement efficiency is a
complex task.
Materials Science: The intense neutron flux and high-energy
particles produced during fusion reactions can damage and degrade
materials over time. Developing materials that can withstand these
harsh conditions while maintaining their structural integrity is crucial.
Energy Balance: Fusion requires an input of energy to initiate and
sustain the reactions. The challenge lies in achieving a net energy
gain, where the energy produced by fusion reactions significantly
exceeds the energy input required to sustain the process.
15
Tritium Fuel Supply: Tritium, a radioactive isotope of hydrogen, is
used as fuel in many fusion reactions. However, tritium is not
naturally abundant and has a relatively short half-life, necessitating a
reliable source and efficient fuel recycling techniques.
Complex Engineering: Building and operating fusion reactors
involve complex engineering challenges, such as designing and
constructing powerful magnets, high-energy laser systems, and
sophisticated plasma containment vessels.
Scale-up: Demonstrating fusion on a small scale (e.g., in a laboratory
experiment) is different from achieving it on a practical power plant
scale. Scaling up the processes while maintaining stability, efficiency,
and safety presents its own set of challenges.
Cost: Fusion research and development require significant
investments in terms of funding, time, and resources. Developing
cost-effective fusion technologies that can compete with other energy
sources is a challenge.
Regulatory and Safety Concerns:
Fusion reactions produce high-energy
neutrons that can induce radioactivity
in materials. Managing and disposing
of radioactive waste and ensuring the
safety of both workers and the
environment are important
considerations.
16
This Photo by Unknown Author is licensed under CC BY-SA
Fusion Reactor concepts :
There are several fusion reactor concepts being explored as potential
pathways to achieving controlled nuclear fusion for energy
generation. These concepts vary in their approaches to confining and
heating the plasma, controlling instabilities, and achieving a net
energy gain. Here are some notable fusion reactor concepts:
Tokamak:
The tokamak is one of the most widely studied and mature fusion
reactor concepts. It uses strong magnetic fields to confine a toroidal
(doughnut-shaped) plasma. The magnetic confinement prevents the
plasma from coming into contact with the walls of the reactor vessel,
allowing the high temperatures and pressures needed for fusion to
occur
17
Notable Examples: ITER, JET (Joint European Torus), EAST
(Experimental Advanced Superconducting Tokamak)
Stellarator:
The stellarator is another magnetic confinement concept that uses
twisted and helical magnetic fields to confine the plasma without
relying on a continuous external current. Stellarators aim to achieve
steady-state plasma operation and avoid some of the instabilities seen
in tokamaks.
Notable Examples: Wendelstein 7-X, LHD (Large Helical Device)
Spheromak:
A spheromak is a compact and simplified fusion concept that
combines elements of both magnetic confinement and self-organized
plasma behavior. It generates its own magnetic fields through plasma
currents and aims to achieve a self-sustained configuration.
18
Notable Examples: SSPX (Spheromak Experiment), CTIX (Current
Drive Experiment)
Magnetic Target Fusion (MTF):
Magnetic Target Fusion seeks to rapidly compress a plasma target
using magnetic fields, generating high temperatures and pressures.
While it shares some characteristics with inertial confinement fusion,
it combines magnetic and inertial approaches.
Notable Examples: University-scale experiments
Inertial Confinement Fusion (ICF):
In this approach, powerful lasers or other external forces are used to
rapidly compress and heat a small pellet of fusion fuel. The resulting
19
high pressure and temperature trigger fusion reactions. It's inspired by
the processes occurring in the cores of stars.
Notable Examples: National Ignition Facility (NIF), Laser Mégajoule
(LMJ)
Field-Reversed Configuration (FRC):
The FRC concept involves a toroidal plasma configuration where the
plasma's magnetic field wraps around itself to form a closed magnetic
structure. It's a self-organized approach that aims to achieve efficient
plasma confinement.
Notable Examples: Tri Alpha Energy, TAE Technologies
Compact Fusion Reactors:
Some private companies and research institutions are working on
novel compact fusion reactor concepts that aim to achieve fusion
power in smaller, more manageable devices. These concepts often
utilize advanced technologies and unique plasma confinement
approaches.
Notable Examples:
SPARC (developed
by Commonwealth
Fusion Systems),
General Fusion,
Tokamak Energy
20
