tokamak

Tokamak is a magnetic confinement fusion device that confines hot plasma in a toroidal, or doughnut-shaped, chamber long enough for fusion. The term tokamak comes from Russian words meaning toroidal chamber with magnetic coils. The concept emerged in the 1950s in the Soviet Union, where researchers led by Igor Tamm and Andrei Sakharov refined the design to improve confinement. The device uses toroidal magnetic fields from external coils and poloidal fields produced by external coils and the plasma current to create a helical field that keeps the plasma from contacting the walls.

Key components include a large vacuum vessel, toroidal field coils, poloidal field coils, and a central solenoid that drives current in the plasma. The plasma current supplies part of the confinement and heats the plasma via ohmic heating; auxiliary heating comes from neutral beam injection and radiofrequency waves. A divertor handles exhaust and impurity control. Plasma temperatures reach tens of millions of kelvin, with confinement guided by the Lawson criterion for future net energy gain.

Current tokamaks include JET in the United Kingdom, which has achieved high-performance plasmas; ITER, under construction in France, intended to demonstrate sustained burning plasmas and net energy production; EAST in China and KSTAR in South Korea, which explore high-performance and steady-state operation.

Challenges remain, including achieving net energy gain, materials capable of withstanding neutron flux, disruption management, and cost-effective scaling. Research focuses on plasma control, heating methods, and reactor materials to enable practical fusion energy.