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Tokamak

A tokamak is a device that uses magnetic fields to confine plasma in a torus (doughnut shape). Its name comes from an acronym of the Russian phrase meaning toroidal chamber with magnetic coils.

Simple Definition (High School)

Section titled “Simple Definition (High School)”

It is a device that wraps coils around a doughnut-shaped vacuum vessel to create a strong magnetic field, then suspends and confines plasma heated to 100 million degrees inside it. It is currently the most extensively researched fusion approach in the world, and ITER, the international experimental reactor under construction in France, is also a tokamak.

Operating Principle (Undergraduate and Above)

Section titled “Operating Principle (Undergraduate and Above)”
  1. Toroidal field coils wound around the torus create a magnetic field that runs the long way around the doughnut ring.
  2. A central solenoid induces a large current (the plasma current) in the plasma itself by the principle of a transformer, and that current creates a poloidal magnetic field that runs around the cross section of the ring.
  3. The helical field lines formed by combining the two magnetic fields confine the plasma stably.

Using the plasma current for confinement is the tokamak’s greatest distinguishing feature. It allows for a simpler structure, but it also gives rise to an inherent challenge called a disruption, in which the current stops abruptly.

Main Components

Section titled “Main Components”
  • Toroidal field coils
  • Central solenoid (for inducing the plasma current)
  • Poloidal field coils (for controlling the plasma’s position and shape)
  • Vacuum vessel
  • Divertor (for exhausting heat and particles)

Representative Devices

Section titled “Representative Devices”
  • ITER (international experimental reactor under construction in France)
  • JET (United Kingdom, recorded a fusion power output of 16.1 MW in 1997)
  • JT-60SA (Japan, one of the world’s largest superconducting tokamaks)
  • KSTAR (South Korea)

Learn More

Section titled “Learn More”
Section titled “Related Terms”