Context: A Tokamak is a nuclear fusion device that uses powerful magnetic fields to confine superhot plasma inside a ring-shaped vacuum chamber, enabling fusion reactions.
It is one of the most extensively researched approaches to achieving controlled nuclear fusion.
The International Thermonuclear Experimental Reactor (ITER), the world's major international fusion research project, is based on the tokamak design.
Despite significant scientific advances, no tokamak has yet generated net energy for commercial electricity production.
What is Nuclear Fusion and Why is Confinement Required?
Nuclear Fusion: A process in which two light atomic nuclei combine to form a heavier nucleus, releasing enormous amounts of energy.
The most extensively studied fusion reaction involves two hydrogen isotopes:
Deuterium + Tritium → Helium + Neutron + Energy
Releases approximately 17.6 MeV of energy.
Plasma: The fourth state of matter, consisting of positively charged ions and free electrons formed when atoms lose their electrons at extremely high temperatures.
Containment problem: Fusion requires temperatures exceeding the Sun's core temperature, making it impossible to contain plasma using ordinary material walls.
Contact with the chamber walls would cool the plasma and introduce impurities, disrupting fusion.
Since plasma contains electrically charged particles, magnetic fields can control and confine it without direct physical contact.
Origin of Tokamak Technology
The tokamak concept was developed in the Soviet Union during the early 1950s, primarily credited to physicists Igor Tamm and Andrei Sakharov.
Experimental development began at the Kurchatov Institute, Moscow, with the first machines operating in the late 1950s.
Its potential subsequently led to adoption by fusion research programmes across several countries.
Why is a Tokamak Ring-shaped?
Magnetic confinement: Charged particles spiral around magnetic field lines.
Problem with a straight tube: Particles can travel along magnetic field lines and escape through the open ends.
Toroidal design: Bending the tube into a closed ring eliminates the ends, allowing magnetic field lines to loop continuously and confine plasma.
Need for an additional magnetic field: In a simple ring, the external magnetic field is stronger on the inner side than the outer side, causing charged particles to drift in opposite directions and pushing plasma towards the chamber walls.
Plasma current: A large electric current is induced through the plasma using a central magnet acting like a transformer. This generates a second magnetic field.
Helical magnetic field: The plasma-generated field twists the original magnetic field lines into a helix, helping cancel particle drifts and improve confinement.
Additional coils: Control the shape and position of plasma within the chamber.
How Does a Tokamak Generate Usable Energy?
Fusion reaction: Deuterium and tritium nuclei combine to produce helium, a neutron and approximately 17.6 MeV of energy.
Energy distribution:
80%: Carried by the high-energy neutron.
20%: Carried by the helium nucleus (alpha particle), which helps heat the plasma.
High energy density: Complete fusion of 1 kg of deuterium-tritium fuel releases approximately joules, nearly 10 million times the energy released by 1 kg of coal.
Blanket system: A thick layer surrounding the plasma chamber absorbs the energy of escaping neutrons and converts it into heat.
Electricity generation: A coolant such as water or helium carries the heat to produce steam, which drives turbines to generate electricity.
Tritium breeding: The blanket contains lithium, which reacts with neutrons to produce tritium, helping the reactor replenish its own scarce radioactive fuel.
Why Have Tokamaks Not Yet Generated Commercial Energy?
Engineering complexity: Maintaining extremely high temperatures, stable plasma confinement and continuous operation requires sophisticated technologies.
Plasma instability: Plasma can develop disturbances that cause energy losses or contact with the chamber walls.
Material limitations: Reactor components must withstand intense neutron bombardment, extreme heat and radiation damage.
Tritium availability: Tritium is scarce and radioactive, requiring an efficient breeding system for commercial reactors.
Energy balance: A reactor must produce more energy than the entire facility consumes, including magnets, heating systems, cooling and other auxiliary equipment.
Commercial viability: Even achieving net fusion energy does not automatically ensure economical electricity generation.
International Thermonuclear Experimental Reactor (ITER)
Objective: Demonstrate the scientific and technological feasibility of controlled magnetic-confinement fusion.
Location: Cadarache, France.
Participants: Seven members — China, European Union, India, Japan, South Korea, Russia and the United States — representing more than 30 countries.
Cost escalation: Initially estimated at €5 billion in 2005, its projected costs have increased at least fourfold.
Revised timeline (2024):
Research operations: 2034.
Deuterium-tritium operations: 2039.
Reasons for delays: COVID-19 pandemic, supply-chain disruptions, quality-control problems and over-optimistic initial planning.
Energy target: Designed to produce 500 MW of fusion power using 50 MW of external plasma-heating power, achieving a plasma energy gain factor (Q) of 10.
Important limitation: ITER is an experimental research facility, not a commercial power plant. It will not convert its fusion heat into electricity.
Current status: ITER is still under assembly and has not yet begun plasma operations; therefore, it has neither succeeded nor failed in demonstrating its fusion-energy target.
China's Progress in Fusion Research
Experimental Advanced Superconducting Tokamak (EAST): Located in Hefei, China; used for research on long-duration plasma confinement.
January 2025: Sustained high-confinement plasma for 1,066 seconds, setting a record for duration, with electron temperatures of approximately 100 million degrees.
January 2026: Reported operation at plasma densities significantly above a longstanding empirical density limit.
Limitation: EAST is an experimental research facility and has not generated net energy.
India's Tokamak Research Programme
Institute for Plasma Research (IPR), Gandhinagar: India's principal institution for fusion and plasma research.
ADITYA:
India's first tokamak.
Began operations in 1989.
Subsequently upgraded as ADITYA-U, which resumed operations in 2017.
SST-1 (Steady State Superconducting Tokamak):
Produced its first plasma in 2013.
Uses superconducting magnets to study long-duration plasma confinement.
India and ITER: India is a member of the ITER project and contributes by manufacturing and supplying specialised reactor components.
PRAGYA:
Developed by Bengaluru-based private company Pranos Fusion.
Described as India's first privately developed compact tokamak.
Intended to develop capabilities in plasma control and magnetic confinement rather than generate commercial electricity.
Alternatives to Tokamak Technology: Fusion research broadly follows two approaches: magnetic confinement and inertial confinement.
Stellarators:
Use complex external magnetic coils to create twisted magnetic field lines without requiring a large current through the plasma.
Can support steady-state operation and avoid certain plasma-current-related instabilities.
However, their complex coil geometry makes design and construction difficult.
Example: Wendelstein 7-X, Germany.
Inertial Confinement Fusion (ICF):
Uses powerful lasers or other energy beams to compress a tiny fuel pellet to extremely high temperatures and pressures.
Fusion occurs before the compressed fuel has time to expand.
Example: US National Ignition Facility (NIF).
In 2022, NIF achieved scientific breakeven, producing more fusion energy than the laser energy delivered to the target. However, the total facility energy consumption remained much higher.
Other magnetic confinement approaches:
Mirror machines: Use magnetic fields that strengthen at both ends to reflect and confine charged particles.
Field-Reversed Configurations (FRCs): Compact magnetic configurations that confine plasma without the central hole characteristic of tokamaks.
Tokamak vs Stellarator vs Inertial Confinement
Feature
Tokamak
Stellarator
Inertial Confinement
Principle
Magnetic confinement
Magnetic confinement
Rapid compression
Configuration
Ring-shaped
Twisted ring-shaped
Tiny fuel pellet
Plasma current
Required in conventional designs
Not required
Not applicable
Major challenge
Plasma instabilities
Complex coil design
Precise, repetitive compression
Example
ITER
Wendelstein 7-X
National Ignition Facility
Important Terms for Prelims
Deuterium: Stable isotope of hydrogen containing one proton and one neutron.
Tritium: Radioactive isotope of hydrogen containing one proton and two neutrons.
Helium nucleus (Alpha particle): Positively charged particle consisting of two protons and two neutrons.
Superconducting magnets: Magnets made using materials that conduct electricity with nearly zero electrical resistance under suitable conditions, enabling powerful magnetic fields.
Plasma energy gain factor (Q): Ratio of fusion energy produced to external energy supplied directly to heat the plasma. Q greater than 1 indicates scientific breakeven at the plasma level, not net electricity generation.
joules, nearly 10 million times the energy released by 1 kg of coal.