Tokamak

Key takeaways

Tokamak belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tokamak to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tokamak from memory before moving on to harder problems.

Reference excerpt

A tokamak (; Russian: токамáк) is a machine which uses a powerful magnetic field generated by external magnets to confine plasma in the shape of an axially symmetrical torus. The tokamak is the leading candidate of magnetic confinement fusion designs being developed to produce controlled thermonuclear fusion power. Tokamaks use a combination of a central solenoid and toroidal and poloidal magnets to shape a ring of plasma. This is heated by a range of methods, including neutral-beam injection, electron and ion cyclotron resonance, lower hybrid resonance. Nuclear fusion may be achieved, measured by neutron detectors. Due to requiring a continuously changing magnetic field, modern tokamaks sustain "plasma discharges" on the timescales of seconds or minutes. The world's largest operational tokamak by radius and plasma current is the JT-60SA in Japan. Other operational experiments include WEST in France and EAST in China. The International Thermonuclear Experimental Reactor (ITER) tokamak is the primary global effort to research fusion power, under construction in France, and aimed for completion by 2034. Many smaller designs, and offshoots like the spherical tokamak, such as at MAST upgrade in UK, continue to be used to investigate performance parameters and other issues. Commercial fusion companies have also proposed tokamak construction in recent years, including Commonwealth Fusion Systems' SPARC design. Tokamaks were first conceptualized by Soviet physicists Andrei Sakharov and Igor Tamm. Experiments were constructed from 1951 at Kurchatov Institute in Moscow led by Lev Artsimovich. Their 1958 T-1 device is sometimes considered the first tokamak. The same year, the USSR, US, and UK began sharing fusion research. A "tokamak stampede" occurred after 1968, when British Culham Laboratory scientists verified high performance results of the Kurchatov Institute's T-3 tokamak. It had been demonstrated that a stable plasma equilibrium requires magnetic field lines that wind around the torus in a helix shape. The z-pinch and stellarator concepts of magnetic confinement had attempted this, but demonstrated serious instabilities. The safety factor (labelled q in mathematical notation) guided tokamak development: tokamaks with q > 1 strongly suppressed these instabilities. By the mid-1970s, dozens of tokamaks were in use around the world. The Princeton Plasma Physics Laboratory (PPPL) in the US became another center of research, beginning with the 1975 Princeton Large Torus. In the late 1970s, the Kurchatov Institute tested the first superconducting magnets and divertors in tokamaks, ubiquitous in modern large designs. The Tokamak Fusion Test Reactor (TFTR),

and the Joint European Torus (JET)

were the first to run experiments with an admixture of rare tritium to deuterium, previous reactors demonstrated fusion in a deuterium plasma. Both reactors developed understanding of alpha particles' role in heating fusion plasma. JET also researched the high-confinement mode, and set magnetic confinement fusion power records standing as of 2025, for energy gain factor (Q = 0.67), total energy output (69 MJ), and fusion power (16 MW).

These machines demonstrated new problems that limited their performance. Solving these would require a much larger and more expensive machine, beyond the abilities of any one country. After an initial agreement between Ronald Reagan and Mikhail Gorbachev in November 1985, the International Thermonuclear Experimental Reactor (ITER) project emerged; construction of the complex began in Cadarache, France in 2013, and tokamak assembly began in 2020.

Etymology The word tokamak is a transliteration of the Russian word токамак, an acronym of either:

or:

The term "tokamak" was coined in 1957 by Igor Golovin, a student of academician Igor Kurchatov. It originally sounded like "tokamag" ("токамаг") — an acronym of the words "toroidal chamber magnetic" ("тороидальная камера магнитная" "toroidál'naya kámera magnítnaya"), but Natan Yavlinsky, the author of the first toroidal system, proposed replacing "-mag" with "-mak" for euphony. Later, this name was borrowed by many languages. The acronym "токамаг" ends in a г, which normally represents a voiced velar stop [g] in Russian orthography, but in Russian this sound devoices to a voiceless velar stop [k] (otherwise written к) at the end of a word, so both spellings are pronounced identically.

History

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Tokamak

Start with the simplest possible case. Write down what Tokamak claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tokamak before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tokamak ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tokamak

In research: Tokamak appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tokamak in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tokamak is common in secondary-school and first-year university syllabi. It links to neighbouring topics Deuterium, Science and technology in the Soviet Union, Soviet inventions, so understanding it makes those chapters shorter.
In everyday life: Look for Tokamak outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Tokamak in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tokamak means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tokamak out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tokamak in simple terms?

A tokamak (; Russian: токамáк) is a machine which uses a powerful magnetic field generated by external magnets to confine plasma in the shape of an axially symmetrical torus. The tokamak is the leading candidate of magnetic confinement fusion designs being developed to produce controlled thermonucl…

Why does Tokamak matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tokamak?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tokamak.