Explain how the tokamak works.
A tokamak is a toroidal vacuum chamber on which coils are wound to create a (toroidal) magnetic field. Air is first evacuated from the vacuum chamber, and then filled with a mixture of deuterium and tritium. Then, with the help of an inductor, a vortex electric field is created in the chamber. The inductor is the primary winding of a large transformer in which the tokamak chamber is the secondary winding. The electric field causes the current to flow and ignite in the plasma chamber.
The current flowing through the plasma performs two tasks: Heats the plasma in the same way as any other conductor would heat it (ohmic heating); Creates a magnetic field around itself. This magnetic field is called poloidal (that is, directed along the lines passing through the poles of the spherical coordinate system). The magnetic field compresses the current flowing through the plasma. As a result, a configuration is formed in which helical magnetic lines of force “wrap” around the plasma filament. In this case, the step during rotation in the toroidal direction does not coincide with the step in the poloidal direction. Magnetic lines turn out to be open, they twist around the torus infinitely many times, forming the so-called. “Magnetic surfaces” of toroidal shape. The presence of a poloidal field is necessary for stable plasma confinement in such a system. Since it is created by increasing the current in the inductor, and it cannot be infinite, the time of stable plasma existence in a classical tokamak is limited. To overcome this limitation, additional methods of maintaining the current have been developed. For this, the injection into the plasma of accelerated neutral atoms of deuterium or tritium or microwave radiation can be used.In addition to toroidal coils, additional coils of the poloidal field are required to control the plasma filament. They are circular loops around the vertical axis of the tokamak chamber.