Explained: How tokamaks hold a star's fire, and where India stands in fusion research
In one line: A tokamak uses magnetic fields to hold plasma hot enough for fusion, and ITER, with India as a partner, is the biggest attempt yet to prove the idea at reactor scale.
Published 6 November 2026. Written by Pratidin from the reports linked at the end; every fact checked by a separate review before publishing. How we work
The Hindu's explainer of 6 November 2026 sets out how tokamaks work and why they are central to the search for fusion power. Fusion joins light nuclei into a heavier one and releases energy. The favoured fuel is deuterium and tritium, two isotopes of hydrogen, which fuse into helium and a fast neutron, releasing 17.6 MeV per reaction, about 80% of it (14.1 MeV) carried by the neutron. The fuel must be heated into a plasma at temperatures of the order of 150 million °C, far hotter than the Sun's core, and no material wall can hold it. A tokamak solves this with magnetism: external coils and an electric current driven through the plasma together create a twisted magnetic field that keeps the plasma inside a ring-shaped vacuum chamber and away from the walls. The name is a Russian acronym for 'toroidal chamber with magnetic coils', and the concept emerged in the Soviet Union in the early 1950s, mainly through Igor Tamm and Andrei Sakharov.
The largest tokamak being built is ITER (International Thermonuclear Experimental Reactor) at Cadarache in southern France. Its seven members are China, the European Union, India, Japan, South Korea, Russia and the United States. India became the seventh full member in December 2005 and supplies about 10% of the components as in-kind contributions, including the 3,850-tonne cryostat built by Larsen & Toubro. ITER aims to produce about 500 MW of fusion power from 50 MW of heating, a gain (Q) of 10, but it is an experiment and will not generate electricity. Under the schedule revised in 2024, operations with deuterium plasma are to begin in 2034 and full deuterium-tritium operation in 2039; the 2016 baseline had planned deuterium-tritium fuel from 2035. In a future power plant, the neutrons would be absorbed in a lithium-bearing blanket, giving heat for steam and breeding new tritium.
India's own programme is based at the Institute for Plasma Research (IPR), Gandhinagar, supported by the Department of Atomic Energy. Its first tokamak, ADITYA, began operating in 1989 and, after an upgrade, resumed as ADITYA-U in 2017; IPR also runs SST-1, a steady-state superconducting tokamak. A Bengaluru start-up, Pranos Fusion, incubated at IPR and JNCASR, has announced PRAGYA, a compact tokamak to test plasma control and superconducting magnets. Elsewhere, China's EAST held a high-confinement plasma for 1,066 seconds in January 2025, and the U.S. National Ignition Facility achieved ignition in December 2022 using lasers, a different route called inertial confinement. The explainer notes that ITER has faced engineering challenges, funding delays and cost escalations, and that it is primarily a physics experiment, not designed to turn heat into electricity.
Prelims facts
- A tokamak confines plasma in a ring-shaped vacuum chamber using magnetic fields from external coils and a current driven through the plasma.
- Deuterium-tritium fusion releases 17.6 MeV per reaction, about 80% of it carried by the neutron.
- ITER, at Cadarache in France, has seven members including India, which joined in December 2005; it aims for a gain of Q = 10 but will not generate electricity.
- Under ITER's 2024 schedule, deuterium plasma operations start in 2034 and deuterium-tritium operation in 2039.
- India's tokamaks, ADITYA-U and SST-1, are at the Institute for Plasma Research, Gandhinagar.
Quick recall
- What does a tokamak use to confine plasma?
- Magnetic fields from external coils and a current driven through the plasma, in a ring-shaped vacuum chamber.
- Energy released by one D-T fusion reaction?
- 17.6 MeV, about 80% of it carried by the neutron.
- Where is ITER being built?
- Cadarache, in southern France.
- When did India become a full member of ITER?
- December 2005, as the seventh member.
- ITER's target fusion gain?
- Q = 10: about 500 MW of fusion power from 50 MW of heating.
- When is ITER to start deuterium-tritium operation under its 2024 schedule?
- 2039.
- Where are India's tokamaks ADITYA-U and SST-1?
- At the Institute for Plasma Research, Gandhinagar.
- Which fusion approach did the U.S. National Ignition Facility use?
- Inertial confinement with lasers.
Prelims practice question
With reference to the International Thermonuclear Experimental Reactor (ITER), consider the following statements:
1. It is being built in France.
2. India is one of its seven members.
3. It is designed to supply electricity to the European grid.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer
Answer: (a) 1 and 2 only. Statements 1 and 2 are correct: ITER is at Cadarache, France, and its seven members are China, the EU, India, Japan, South Korea, Russia and the U.S. Statement 3 is wrong: ITER is an experiment that will not generate electricity.
Use this in UPSC Mains: previous-year questions
Recurring theme: Nuclear fusion, ITER and India's role in frontier energy research
- How to use this
Use India's in-kind ITER contributions and its domestic tokamaks for the first part, and ITER's Q = 10 goal and limits for the implications.
- India became ITER's seventh full member in December 2005 and supplies about 10% in kind, including L&T's 3,850-tonne cryostat.
- India's ADITYA tokamak began in 1989 and was upgraded as ADITYA-U in 2017; IPR Gandhinagar also runs SST-1.
- ITER targets 500 MW from 50 MW of heating (Q = 10) but will not generate electricity; D-T operation is planned for 2039.
- How to use this
Use fusion research as a long-term, low-carbon option in a forward-looking conclusion on energy security, while noting its distant timeline.
- Deuterium-tritium fusion releases 17.6 MeV per reaction; a lithium blanket would turn the neutrons' energy into heat for steam and breed tritium.
- India is an ITER member and runs ADITYA-U and SST-1 at IPR Gandhinagar.
- ITER's deuterium-tritium operation is planned only for 2039, so fusion cannot meet near-term energy needs.
ITER tests fusion at reactor scale, so its success would help members build fusion reactors, answer (d).
Mains practice question
Explain the working principle of a tokamak. What are the major scientific and engineering challenges in making fusion a source of commercial electricity? (150 words)
Model answer
A tokamak is a doughnut-shaped device that uses magnetic fields to confine extremely hot plasma so that light nuclei can fuse and release energy.
Working principle
- Deuterium and tritium are heated to a plasma of the order of 150 million °C.
- External coils and a current through the plasma create a twisted magnetic field that keeps it off the walls.
- Each D-T fusion releases 17.6 MeV; about 80% goes to the neutron, whose heat a future plant would capture in a lithium blanket.
Challenges
- Materials: walls must survive intense heat and neutron damage.
- Plasma stability: instabilities can end a pulse; EAST held a high-confinement plasma for 1,066 seconds only in January 2025.
- Tritium: it must be bred from lithium at scale.
- Cost and time: ITER's deuterium-tritium operation has slipped to 2039.
- Net energy is not electricity: ITER targets Q = 10 but will not generate power.
Fusion is promising, but commercial power remains decades away.
The basics
Why this matters
Fusion powers the Sun. If it can be tamed on Earth, it promises large amounts of energy from abundant fuel, with no carbon dioxide from combustion and far less long-lived waste than fission. India is a partner in the biggest fusion experiment ever built and runs its own machines. Tokamaks, the leading design, are a regular Prelims topic.
Fission and fusion
Nuclear power plants today use fission: a heavy nucleus such as uranium splits. Fusion is the opposite: light nuclei join. See Nuclear fusion. Fusion needs nuclei to collide at enormous speed, which means extreme heat. At such temperatures, matter becomes plasma, a gas of charged particles. The challenge is holding it.
- Heavy nuclei such as uranium split
- Used in today's nuclear power plants
- Produces long-lived radioactive waste
- Light nuclei such as deuterium and tritium join
- Still experimental; no commercial plant yet
- Fuel is abundant, but tritium must be bred from lithium
How a tokamak holds plasma
Charged particles follow magnetic field lines. A Tokamak bends the field into a closed ring, so particles circle forever without touching a wall. Coils outside the chamber make one field; a current driven through the plasma itself makes another. Together they form a twisted field that holds the plasma steady. A related design, the stellarator, makes the twist with complex external coils alone.
- 1Vacuum vesselRing-shaped chamber that holds the plasma.
- 2Magnetic coilsCreate the field that confines the plasma.
- 3Plasma currentAdds the twist to the field and helps heat the plasma.
- 4BlanketAbsorbs neutrons for heat and breeds tritium from lithium.
- 5CryostatKeeps superconducting magnets extremely cold; ITER's was built by L&T.
India's place
India joined ITER in December 2005. At home, the Institute for Plasma Research in Gandhinagar runs ADITYA-U and SST-1. Other routes exist: Inertial confinement fusion uses lasers to crush fuel pellets, and achieved ignition at the U.S. National Ignition Facility in December 2022.
- Early 1950sTamm and Sakharov develop the tokamak concept in the Soviet Union.
- 1989India's ADITYA tokamak begins operation at IPR.
- December 2005India becomes the seventh full member of ITER.
- December 2022National Ignition Facility achieves ignition with lasers.
- January 2025China's EAST sustains high-confinement plasma for 1,066 seconds.
- 2039ITER's planned start of deuterium-tritium operation.
Go deeper
Why it matters for UPSC
Fusion, ITER and India's research institutions appear in both Prelims and Mains. UPSC asked about ITER in Prelims 2016 and Mains 2025. The topic also links to energy security and clean energy goals.
The core idea
Nuclear fusion joins light nuclei and releases energy, but only at temperatures no wall can withstand. A Tokamak avoids walls by holding the plasma with twisted magnetic fields in a ring. ITER in France will test this at a scale that should give ten times more fusion power than heating power. India contributes components and runs its own machines at the Institute for Plasma Research. A rival route, Inertial confinement fusion, crushes fuel with lasers.
Numbers and dates to remember
- 17.6 MeV per D-T reaction; about 80% to the neutron.
- ITER: 7 members; India joined December 2005; about 10% in-kind share.
- ITER: 500 MW from 50 MW (Q = 10); D-T operation planned for 2039.
- ADITYA from 1989; ADITYA-U from 2017.
- EAST: 1,066 seconds, January 2025.
Where to go next
- Nuclear fusion: the physics of joining nuclei.
- Tokamak: how magnets hold a plasma.
- ITER: the international experiment India is part of.
- Institute for Plasma Research: India's home for fusion research.
- Inertial confinement fusion: the laser route to fusion.
Go deeper: is fusion worth the wait?
Supporters make three points. Fusion fuel is abundant: deuterium comes from water and tritium can be bred from lithium. A fusion reaction cannot run away like a fission chain reaction; if confinement fails, the plasma cools and stops. And it produces no carbon dioxide from combustion. For a country with growing energy demand, these are strong reasons to stay in the race, which is why India joined ITER in 2005 and keeps its own Institute for Plasma Research active.
Sceptics point to time and cost. ITER's schedule has slipped: the 2016 baseline planned deuterium-tritium fuel from 2035, it is now planned for 2039, and costs have risen sharply. Even a successful ITER will not make electricity; a demonstration power plant must come after it. The engineering problems are severe: materials that survive intense neutron bombardment, stable plasmas in a Tokamak for long periods, and tritium breeding at scale.
There is also competition between methods. Inertial confinement fusion reached ignition at the U.S. National Ignition Facility in 2022, but the energy counted excluded the far larger energy used to power the lasers. In India, the start-up Pranos Fusion is designing a compact tokamak and a high-temperature superconducting magnet programme.
For India, the payoff from ITER is not only future power. Indian industry has built some of ITER's most demanding parts, such as the cryostat, and this know-how in cryogenics, superconducting magnets and power systems is useful far beyond Nuclear fusion.
Nuclear fusion
The physics of joining nuclei.
In one line: Nuclear fusion is the joining of two light atomic nuclei into a heavier one, releasing energy, the process that powers the Sun.
How it works
Nuclei are positively charged and repel each other. To fuse, they must collide at very high speeds, which needs temperatures of the order of 100 million °C or more. At such heat, matter becomes plasma.
The best fuel
Deuterium and tritium, two isotopes of hydrogen, fuse most easily. They produce helium and a neutron and release 17.6 MeV, about 80% of it with the neutron. Tritium is radioactive and scarce, so reactors must breed it from lithium in a blanket around the plasma.
Why it is in the news
The Hindu's 6 November 2026 explainer sets out how tokamaks make fusion possible.
Where to go next
Tokamak
How magnets hold a plasma.
In one line: A tokamak is a doughnut-shaped device that uses magnetic fields to confine plasma for fusion.
How it works
Charged particles spiral along magnetic field lines. External coils create a field around the ring, and a current driven through the plasma adds a second field. Together they make a twisted field that holds the plasma off the walls. The name is a Russian acronym for 'toroidal chamber with magnetic coils'.
History
The concept came from the Soviet Union in the early 1950s, mainly through Igor Tamm and Andrei Sakharov, and tokamaks became the leading fusion design.
Examples
ITER (France), EAST (China), ADITYA-U and SST-1 (India), and the new PRAGYA design from Bengaluru's Pranos Fusion.
Where to go next
ITER
The international experiment India is part of.
In one line: ITER, the International Thermonuclear Experimental Reactor, is the world's largest tokamak, being built at Cadarache in France by seven partners.
Members and India's role
China, the European Union, India, Japan, South Korea, Russia and the U.S. India became the seventh full member in December 2005 and supplies about 10% as in-kind contributions, including the 3,850-tonne cryostat by Larsen & Toubro, cryolines, power supplies and heating systems.
Goals and schedule
About 500 MW of fusion power from 50 MW of heating (Q = 10). It will not generate electricity. Under the 2024 schedule, deuterium plasma operations begin in 2034 and deuterium-tritium operation in 2039.
Where to go next
Institute for Plasma Research
India's home for fusion research.
In one line: The Institute for Plasma Research in Gandhinagar, supported by the Department of Atomic Energy, runs India's tokamaks and anchors its role in ITER.
Its machines
- ADITYA: India's first tokamak, commissioned in 1989.
- ADITYA-U: the upgraded machine, operating from January 2017.
- SST-1: a steady-state superconducting tokamak for studying long plasma confinement.
Wider role
IPR has also incubated Pranos Fusion, a Bengaluru start-up designing a compact tokamak called PRAGYA.
Where to go next
Inertial confinement fusion
The laser route to fusion.
In one line: Inertial confinement fusion squeezes a tiny fuel pellet with lasers or particle beams so fast that it fuses before it can fly apart.
How it differs from tokamaks
A tokamak holds plasma for seconds or minutes with magnets. Inertial confinement lasts a tiny fraction of a second and relies on the fuel's own inertia.
The landmark
The U.S. National Ignition Facility achieved ignition in December 2022, getting more fusion energy out of the pellet than the laser energy delivered to it. The energy needed to power the lasers was far larger, so it was not net energy for a power plant.
Why it matters
It shows fusion can release more energy than it receives, but practical power needs repeated shots many times a second.
Where to go next
Take the 6 November 2026 quiz: 30 Prelims-style questions with answers