How does a tokamak fusion reactor work?

In one line

The rule

Fusion is the process where two light atomic nuclei combine to form a heavier nucleus, releasing energy.

The energy released is given by the formula: E = mc², where:

• E is energy (in joules)
• m is the loss in mass (in kilograms)
• c is the speed of light (about 3 × 10⁸ m/s)

Let's understand it simply

Imagine you want to make two small balls stick together, but they keep pushing each other away. This is like two hydrogen nuclei (protons) in the sun. If you push them hard enough, they join and release a burst of energy.

But on Earth, it is not easy. The nuclei need to be extremely hot—hotter than the sun's core—so they move fast enough to overcome their repulsion. A tokamak is a special machine that holds this super-hot gas (called plasma) in a ring, using magnets, so the nuclei can crash into each other and fuse.

Think of it like holding a very hot, spinning jalebi with invisible hands (the magnets), so it doesn't touch the plate (the walls) and cool down.

How it works

1. Fuel injection: Light atoms (usually deuterium and tritium, types of hydrogen) are put into the tokamak.
2. Heating: The fuel is heated to over 100 million °C, turning it into plasma (a state where electrons are free from atoms).
3. Magnetic confinement: Strong magnets create a donut-shaped (toroidal) magnetic field that traps the plasma and keeps it away from the walls.
4. Plasma control: Extra magnetic coils shape and stabilize the plasma, so it doesn't touch the walls and cool down.
5. Fusion reaction: In the hot, dense plasma, nuclei collide, fuse, and release energy (mostly as fast neutrons).
6. Energy extraction: The fast neutrons hit a blanket around the plasma, heating it up. This heat can be used to make steam and turn turbines for electricity.

The story behind it

The tokamak was invented in the 1950s by Soviet scientists Igor Tamm and Andrei Sakharov, in Russia. They wanted to find a way to control fusion on Earth, to make clean and almost limitless energy. The word "tokamak" comes from Russian words meaning "toroidal chamber with magnetic coils."

One memorable detail: Early tokamaks were so secret that Western scientists were shocked by their success when they finally saw them in the 1960s.

Where you see it in real life

• International Thermonuclear Experimental Reactor (ITER), France → The world's largest tokamak, being built by many countries.
• EAST (China) → A tokamak that set records for how long it can hold plasma.
• K-STAR (Korea) → Another advanced tokamak, aiming for steady fusion.
• JET (UK) → The first tokamak to produce significant fusion power.
• Inside the sun → Not a tokamak, but the same fusion process happens naturally.
• Fusion research labs in India (e.g., Institute for Plasma Research, Gujarat) → Indian scientists work on tokamaks like ADITYA and SST-1.

Why it matters

• Clean energy: Fusion makes no greenhouse gases and little radioactive waste.
• Fuel from water: Deuterium is found in seawater, so fuel is almost unlimited.
• No meltdown risk: Unlike nuclear fission, fusion reactors can't explode like Chernobyl.
• Future jobs: Engineers, physicists, and technicians will be needed for fusion power plants.
• Foundation for exams: Fusion and tokamaks are important in CBSE Physics, and for competitive exams like NEET, JEE.

Worked example

Let's see how much energy comes from fusing 1 gram of deuterium and tritium:

Given: m (mass lost in fusion) ≈ 0.018 grams = 0.000018 kg
Step 1: Write the rule        E = m × c²
Step 2: Put in the numbers    E = 0.000018 × (3 × 10⁸)²
Step 3: Calculate             E = 0.000018 × 9 × 10¹⁶
Step 4: Answer                E = 1.62 × 10¹² joules (very large!)

This is enough to run a small Indian town for a day!

Common mistakes

• Thinking the plasma touches the walls: It must not. If it does, it cools and fusion stops.
• Confusing fission and fusion: Fission splits heavy atoms (like uranium); fusion joins light atoms (like hydrogen).
• Believing fusion is easy: It is very hard to keep plasma hot and stable for long.
• Assuming tokamaks produce electricity directly: They make heat, which is then used to make steam and turn turbines.

Remember it

Tokamak = "magnetic donut" that traps super-hot plasma so hydrogen nuclei can fuse—like making a mini sun on Earth.