Tokamak

In a tokamak, the plasma is the central component of the device. It is a state of matter consisting of highly ionized gas composed of positively charged ions and negatively charged electrons. The plasma is created and confined within the toroidal chamber of the tokamak using magnetic fields. In other words, in a tokamak, a doughnut-shaped vacuum chamber is used to confine the plasma. Strong magnetic fields are applied to confine and shape the plasma, preventing it from coming into contact with the chamber walls and minimizing heat losses. The primary magnetic field is generated by a large toroidal (doughnut-shaped) coil surrounding the plasma chamber, while additional magnetic fields are produced by smaller poloidal coils within the chamber.

The charged particles moving in a magnetic field follow a helical path around the field lines owing to Lorentz force, they stick to the magnetic lines and possible movement perpendicular to the field in this way is highly restricted. This effect serves on basis for hot plasma.

Consider a simple torus in which the magnetic lines of force are circular and close upon themselves. In a simple torus in which lines of forces are closed circle, the magnetic field varies as 1/r and hence arise gradient in magnetic field.

A vertical electric field is created as a result of the ensuing magnetic field drift, which pushes ions and electrons further to the top and bottom of the ions, respectively. This field E causes the plasma to drift away from the major axis, i.e., ions and electrons e-drift together in the direction E x B.

To avoid this effect toroidal system require to twist in the lines of force as shown i.e neutralizes the charges that are separated.

The primary toroidal magnetic field in a tokamak is created by a group of coils that are positioned around the doughnut-shaped plasma chamber. An immense transformer's single secondary winding is the conducting plasma itself. A large current is introduced into the secondary winding, or the plasma ring itself, by a current pulse in the primary winding. A poloidal magnetic field is produced by the induced plasma current. As demonstrated, a helical magnetic field is produced when this poloidal field interacts with the primary toroidal field.

The magnetic structure thus generated consists of an infinite set of nested toroidal magnetic surfaces each with a slightly different twist, reducing the further leakage of particles and heat from the plasma.

Toroidal field B+ is produced by ordinary type of coils. Poloidal field Bp is produced by a large plasma current induced by a transformer.

To overcome the poloidal magnetic field, which is a current ring's inherent inclination to expand, the third field, Bv, in the vertical direction is required. Because Bp²/ 8π is large on the interior, the plasma's main radius tends to grow. J x Bv is radially inward as a result of the field Bv's downward direction. An external coil can be created by the field. In order for fusion processes to occur, the plasma must reach certain temperatures and densities. The fusion processes in a deuterium-tritium plasma result in the production of helium and the release of a significant quantity of energy in the form of high-energy neutrons.

The challenge in tokamak research is to sustain and control the plasma for a sufficient amount of time to achieve a self-sustaining fusion reaction, known as a "burning plasma." Researchers are continually working to optimize the design of tokamaks and improve plasma confinement to make fusion energy a practical and sustainable source of electricity.

Tokamaks play a crucial role in fusion energy research and are of significant importance for several reasons:

1. Advancing Fusion Energy: Tokamaks are the leading technology for achieving controlled fusion reactions, which have the potential to provide a nearly limitless, safe, and environmentally friendly source of energy. By studying and optimizing tokamak designs, scientists aim to develop practical fusion reactors that can produce sustainable electricity.

2. Plasma Confinement: Tokamaks allow researchers to study plasma confinement, which is a critical aspect of fusion reactions. Understanding how to effectively confine and control plasma is essential for achieving the necessary conditions for sustained fusion reactions. Tokamaks enable scientists to investigate different techniques for plasma confinement and develop improved methods for maintaining the stability and performance of the plasma.

3. Fusion Plasma Physics: Tokamaks serve as valuable tools for studying the physics of high-temperature plasmas. They provide a controlled environment where scientists can investigate various plasma phenomena, such as turbulence, instabilities, and particle interactions. These studies deepen our understanding of plasma physics and help to refine theoretical models and simulation codes used to predict and optimize plasma behavior.

4. Materials and Engineering Challenges: Tokamaks face significant engineering and materials challenges due to the extreme conditions inside the plasma chamber, including high temperatures, intense radiation, and strong magnetic fields. Developing materials that can withstand these conditions is crucial for the success of future fusion reactors. Tokamaks serve as test beds for exploring new materials, testing their performance, and improving engineering designs to ensure the safe and efficient operation of fusion power plants.

5. International Collaboration: The development and operation of tokamaks have fostered extensive international collaboration. Projects like ITER (International Thermonuclear Experimental Reactor) bring together scientists, engineers, and researchers from numerous countries, pooling their expertise and resources to advance fusion research. Collaboration on tokamaks helps share knowledge, accelerate progress, and build a global community focused on realizing fusion energy.

In summary, tokamaks are of paramount importance as they provide a platform for studying and advancing fusion energy, investigating plasma physics, addressing engineering challenges, and fostering international collaboration. They are instrumental in our quest to achieve sustainable and clean fusion power.

This note is a part of the Physics Repository.