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Test: How a Tokamak Works and How Much Energy It Has Managed to Obtain from Fusion So Far

April 28, 2026 · 7 min read

Question: How does a tokamak work and how much energy has it managed to obtain from fusion reactions so far?

Perplexity

A tokamak is a toroidal (doughnut-shaped) chamber with magnetic coils designed to magnetically confine plasma at the millions of degrees Celsius temperatures required for thermonuclear fusion. The device operates on the principle of creating a powerful toroidal magnetic field: coils around the chamber's perimeter form a "closed tunnel" that holds the superheated plasma, preventing it from touching and melting the walls. Before startup, the air is pumped out of the chamber and it's filled with a mixture of deuterium (a hydrogen isotope with a proton and a neutron in its nucleus) and tritium (a proton + two neutrons). An electric current, induced by a central transformer, accelerates the plasma, creating a vortex field: this simultaneously heats the gas to millions of degrees Celsius and provides the poloidal component of the magnetic field for the stability of the "plasma cord." Under these conditions, deuterium and tritium nuclei overcome Coulomb repulsion, fuse into a helium nucleus, releasing a neutron and a huge amount of energy – many times more than in chemical reactions.

A key feature of the tokamak is its pulsed operation: the current in the inductor grows limitedly, so reactions last for seconds or minutes, and to extend the pulses, additional heaters like neutral particle beams are used. Neutrons born in the reaction pass through the magnetic field, heating the reactor walls (cooled by water), which allows heat to be converted into steam for turbines. Soviet scientists (Sakharov, Tamm) proposed the concept in the 1950s, and the first tokamak was created in 1954–1957; today, such devices exist in Russia (T-15MD, launched in 2021, heated to 11 million °C), China (EAST), Europe (JET), and other countries.

Regarding energy output, tokamaks have not yet achieved a net energy gain (Q > 1, where output exceeds input). The record-holder ITER (under construction in France) aims for Q=10, but experiments so far yield Q around 0.67: for example, JET in 1997 produced 16 MJ in 0.1 seconds with an input of 24 MJ. The Russian T-3 heated plasma to 11 million °C, but without specifying the exact output; modern installations focus on plasma stability rather than net energy – commercial fusion is expected after 2035.

Sources:

  • Hi-News.ru: "What is a Tokamak: Simply About a Fusion Reactor"
  • Wikipedia: "Tokamak"
  • RIAMO: "Artificial Sun: What is a Tokamak and Which Countries Have It"
  • NRC.KI: ""Tokamak-10". How Fusion Works"
  • OSN Media: "Tokamak: What It Is, Acronym, Principle of Operation, History"

Gemini

A tokamak is a device for plasma confinement using a magnetic field, designed to achieve a controlled thermonuclear reaction. The principle of operation of a tokamak is based on creating a toroidal (ring-shaped) chamber, inside which plasma – an ionized gas heated to extremely high temperatures (hundreds of millions of degrees Celsius) – is confined by strong magnetic fields. The magnetic field has a complex configuration, including both external magnetic coils and a current flowing directly within the plasma. This current not only helps to confine the plasma but also heats it. In tokamaks, isotopes of hydrogen – deuterium and tritium – are typically used for the fusion reaction. When these nuclei collide, they merge, releasing a large amount of energy and forming a helium nucleus and a neutron.

Regarding the energy produced, to date, no tokamak has been able to produce more energy than was consumed to operate it. However, significant progress has been made. For example, in the JET (Joint European Torus) experiment in 1997, 22 megajoules of energy were obtained from the fusion reaction, which was a record at the time. In December 2023, the JT-60SA tokamak in Japan managed to confine plasma for 100 seconds at a temperature above 100 million degrees Celsius, which is an important step towards achieving sustained thermonuclear burning. The ITER (International Thermonuclear Experimental Reactor) project, under construction in France, aims to demonstrate the possibility of obtaining 10 times more energy than is consumed and to become the first fusion reactor to produce energy on an industrial scale.

Sources:

  • Rosatom
  • ITER

ChatGPT

A tokamak is a device for thermonuclear fusion that uses a strong magnetic field to confine hot plasma in a toroidal (ring) shape. The main task of a tokamak is to confine and control a plasma of deuterium and tritium ions at extremely high temperatures (up to hundreds of millions of degrees Celsius) to initiate a thermonuclear fusion reaction. The magnetic field is generated by a combination of external magnetic coils and the current flowing within the plasma, which helps prevent its contact with the installation walls and energy loss.

In recent years, the largest and most well-known project is the international experimental reactor ITER, which is being built with the aim of demonstrating a positive energy balance from the fusion reaction. Prior to this, the largest successful tokamak experiments had already recorded significant achievements. For example, in 2022, the Chinese tokamak EAST achieved plasma with a temperature of around 120 million degrees Celsius for 101 seconds, demonstrating confinement stability. Earlier, in 2021, an American tokamak achieved a breakthrough – it released approximately 59 megajoules of thermal energy in 9 seconds, which was the best result for plasma confinement and the amount of energy released.

However, so far, no tokamak has achieved an energy "output/input" ratio greater than 1, meaning it has not produced more energy than it consumed for its startup and confinement. In the summer of 2023, at the NIF (National Ignition Facility) tokamak in the USA, a record short-term reaction was achieved with an energy output slightly exceeding the input, which was an important step towards commercial fusion, but this was not a tokamak, but laser confinement. ITER, in the future, plans to achieve an energy gain factor of around 10 by approximately 2035, which would be a revolution for the energy sector.

Sources:

  • ITER - Official Website
  • News from the Chinese Tokamak EAST
  • Lawrence Livermore National Laboratory (LLNL) for the NIF Project
  • Scientific American, reviews on thermonuclear fusion

Grok

A tokamak is a toroidal (doughnut-shaped) device designed for magnetic confinement of plasma under conditions necessary for thermonuclear fusion. The basic principle of operation: extremely powerful magnetic fields, generated by external superconducting coils, form a "magnetic cage." The toroidal field is created by toroidal solenoids around the chamber, and the poloidal field is created by an induced electric current in the plasma itself, which is initiated by a central solenoid. Gas, typically deuterium and tritium (or deuterium), is introduced into a vacuum chamber, ionized into plasma, and heated to 100–150 million degrees Celsius using neutral beams, radiofrequency heating, or electron cyclotron resonance. When the required density, temperature, and confinement time (Lawson criterion) are reached, deuterium and tritium nuclei fuse, releasing energy in the form of neutrons and alpha particles.

Despite progress, tokamaks have not yet achieved a net energy gain (Q>1, where fusion produces more energy than it consumes). The record for energy directly obtained from a fusion reaction in a tokamak is 69.26 MJ – this was achieved by the British JET in 2024 over 5 seconds of operation with a plasma power of approximately 16 MW. The previous record was 59 MJ in 2021 on the same JET. In 2025–2026, plasma confinement time records were updated (WEST – 1337 seconds, EAST – 1066 seconds), but in terms of fusion energy output, JET's lead has not been surpassed; private projects like Tokamak Energy's ST40 boast records for plasma current (1 MA) and "triple product," but not for fusion energy yield.

Sources:

Claude

How a Tokamak Works and Its Energy Achievements

Principle of Operation

A tokamak (toroidal chamber with magnetic coils) is a toroidal device for magnetic confinement of plasma to achieve the conditions necessary for controlled thermonuclear fusion. The device operates on the principle of a transformer: the central solenoid serves as the primary winding, and the plasma itself acts as the secondary, single-turn winding. The plasma is confined by a specially created combined magnetic field – a toroidal external field and a poloidal field from the current flowing through the plasma column. The current in the tokamak creates the magnetic field component necessary for plasma confinement and heats the plasma. This design allows for achieving the extremely high temperatures required for fusion.

Current Energy Results

To date, no tokamak has produced net energy – they all remain experimental installations. However, significant progress has been made in other parameters. The European tokamak JET achieved a record 69 MJ of energy during a 5-second fusion reaction. In terms of plasma confinement duration, researchers at the WEST Tokamak managed to sustain a plasma reaction for over 22 minutes, setting a new world record. In the Chinese city of Chengdu, the HL-3 facility achieved a historic result: the ion temperature in its plasma exceeded 100 million degrees Celsius, and the energy confinement efficiency approached the levels required to initiate a fusion reactor. Modern experimental tokamaks do not produce any fusion energy; they investigate plasma, materials, and control systems; on some installations, the energy gain factor has not exceeded unity.

Sources:

  • Princeton Plasma Physics Laboratory
  • Atomic Energy Agency (IAEA)
  • CEA (French Alternative Energies and Atomic Energy Commission)
  • Energy Singularity (China)

Sources: