AR Technology Part 4: Entering the Tokamak

Tokamak is a toroidal container that uses magnetic confinement to achieve controlled nuclear fusion. It was first invented in the 1950s by Azimovich and others at the Kurchatov Institute in Moscow, the Soviet Union. The center of the tokamak is a toroidal vacuum chamber with coils wrapped around it. When the power is turned on, a huge spiral magnetic field is generated inside the tokamak, heating the plasma inside to a very high temperature to achieve the purpose of nuclear fusion.

Why do we need to use the tokamak device to perform nuclear fusion? Nuclear fusion refers to the process of small-mass atoms, mainly deuterium, under certain conditions (such as ultra-high temperature and high pressure), allowing two atomic nuclei to attract each other and collide together, and the atomic nuclei will aggregate to generate new atomic nuclei with heavier mass. Although neutrons are relatively large in mass, they are not charged, so they can also escape from the constraints of the nucleus and be released during this collision. The release of a large number of electrons and neutrons is manifested as a huge release of energy. Nuclear fusion releases safe, efficient and clean energy. In addition, the hydrogen bomb explosion that humans can currently achieve belongs to uncontrolled nuclear fusion, and the tokamak device is our current mainstream way to achieve controlled nuclear fusion.

There are four key components in the tokamak device, namely the internal and external cold screens. The function of the internal and external cold screens is to effectively reduce the heat load of the EAST superconducting magnet. The 80K internal and external cold screens are set between the superconducting magnet and the vacuum chamber and between the superconducting base and the external vacuum dewar. The cold screens are cooled by liquid nitrogen or liquid ammonia. On one side of the EAST is a plasma with a temperature of up to 100 million degrees, and on the other side is a superconducting coil cooled to an extremely low temperature of minus 269 degrees. The shortest straight-line distance between the two is only 1.2 meters. In order to resolve the contradiction between the two, EAST has internal and external cold screens, which isolate the heat from the superconducting coils and the internal isotropic body and the external atmosphere through vacuum insulation.

Superconducting poloidal field coils are composed of a central spiral tube and a matching large coil that are symmetrically distributed up and down. The coils adopt a CICC conductor design scheme, the superconducting material is NbTi, and are cooled by supercritical 4.5K ammonia forced flow.

Superconducting longitudinal field coil, the superconducting longitudinal field coil is composed of sixteen D-shaped coils evenly distributed in the toroidal direction. The system can generate a toroidal field of 3.5T at the center of the plasma, and its total ampere-turns is 30MAT.

The outer vacuum dewar is a cylindrical structure, which is divided into three parts: the dome cover, the middle ring and the base. The outer vacuum dewar mainly provides a vacuum environment for components such as the poloidal field and longitudinal field vacuum chambers, and isolates the heat exchange generated by the external environment to these large components. At the same time, it will bear the loads imposed by the large components of the device. The dewar is the outermost layer of the mainframe, which seals other internal components in a vacuum environment. When EAST is working, the atmospheric pressure inside the mainframe can be as low as one hundred millionth of the atmospheric pressure.

With the continuous development of science and technology, scientists have found that experimental research has also found a variety of modes to improve confinement. According to these modes, the economic performance of tokamak nuclear fusion reactors can be further improved. Based on the major progress made in plasma theory, physical experimental research and engineering technology over the past 50 years, the International Thermonuclear Experimental Reactor (ITER) project, a super-large international cooperation project jointly participated by seven parties, has entered the engineering construction stage.

In the future, in the field of nuclear fusion, Tokamak will continue to provide people with safer, cleaner and more efficient energy.