Physics:Tokamak physics

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Conceptual illustration of tokamak physics, showing magnetic confinement of high-temperature plasma, external heating methods, and transport processes governing confinement and edge behavior.

Overview

A tokamak is a device designed to confine high-temperature plasma using magnetic fields in order to achieve controlled nuclear fusion.

It is the most widely studied configuration for fusion energy and is used in experiments such as:

  • DIII-D
  • JET
  • ITER[1]

Basic principle

Fusion requires:

  • Extremely high temperatures (~10⁸ K)
  • Sufficient particle density
  • Long confinement time

These conditions are summarized by the Lawson criterion.

In a tokamak, plasma is confined in a toroidal (donut-shaped) geometry using magnetic fields.

Magnetic confinement

Charged particles spiral around magnetic field lines due to the Lorentz force:

𝐅=q(𝐄+𝐯×𝐁)

Tokamaks use two main magnetic fields:

  • Toroidal field (around the donut)
  • Poloidal field (around the cross-section)

Together, these create helical field lines that improve confinement.[1]

Plasma current

A strong electric current flows through the plasma:

  • Generates the poloidal magnetic field
  • Heats the plasma (ohmic heating)

This current is essential for confinement but also introduces instabilities.

Stability and confinement

Plasma stability is governed by magnetohydrodynamics (MHD).

Important concepts:

  • Safety factor q
  • Magnetic shear
  • Instabilities (kink, tearing modes)

Maintaining stability is crucial for sustained operation.[2]

Heating methods

Additional heating is required to reach fusion temperatures:

  • Neutral beam injection
  • Radio-frequency heating
  • Ohmic heating

These methods increase particle energy and sustain the plasma.

Transport and losses

Particles and energy are not perfectly confined.

Loss mechanisms include:

  • Diffusion
  • Turbulence
  • Drift effects

Transport processes determine how long plasma can be confined.

Divertor and edge region

The edge of the plasma includes:

  • Scrape-off layer (SOL)
  • Divertor region

In this region:

  • Magnetic field lines intersect material surfaces
  • Particles are exhausted and recycled

This region is critical for:

  • Heat removal
  • Plasma-wall interaction
  • Impurity control

Connection to edge physics

The behavior of the edge plasma strongly influences overall performance.

Key phenomena:

  • Drift-driven transport
  • Plasma rotation
  • Recycling of neutrals

These effects determine how particles are distributed at the divertor.

Detailed studies are presented in:

Physical interpretation

Tokamaks represent a controlled environment where:

  • Electromagnetic forces dominate
  • Collective plasma behavior emerges
  • Macroscopic confinement arises from microscopic particle motion

They are a key application of plasma physics and kinetic theory.

Summary

Tokamak physics:

  • Uses magnetic fields to confine plasma
  • Combines kinetic, fluid, and electromagnetic effects
  • Enables experimental study of fusion energy

It forms the direct link between plasma theory and practical fusion devices.

See also

    Foundations

  1. Physics:Quantum basics
  2. Physics:Quantum mechanics
  3. Physics:Quantum mechanics measurements
  4. Physics:Quantum Mathematical Foundations of Quantum_Theory

    5. Conceptual and interpretations

  5. Physics:Quantum Interpretations of quantum mechanics
  6. Physics:Quantum A Spooky Action at a Distance
  7. Physics:Quantum A Walk Through the Universe
  8. Physics:Quantum: The Secret of Cohesion: How Waves Hold Matter Together

    9. Mathematical and solvable systems

  9. Physics:Quantum Exactly solvable quantum systems
  10. Physics:Quantum Formulas Collection
  11. Physics:Quantum A Matter Of Size

    12. Symmetry and structure

  12. Physics:Quantum Symmetry in quantum mechanics
  13. Physics:Quantum Matter Elements and Particles

    14. Atomic and spectroscopy

  14. Physics:Quantum Atomic structure and spectroscopy

    15. Quantum wavefunctions and modes

  15. Physics:Number of independent spatial modes in a spherical volume

    16. Quantum information and computing

  16. Physics:Quantum information theory
  17. Physics:Quantum Computing Algorithms in the NISQ Era
  18. Physics:Quantum_Noisy_Qubits

    19. Quantum optics and experiments

  19. Physics:Quantum Nonlinear King plot anomaly in calcium isotope spectroscopy
  20. Physics:Quantum optics beam splitter experiments
  21. Physics:Quantum Ultra fast lasers
  22. Physics:Quantum Experimental quantum physics
  23. Template Quantum optics operators

    24. Open quantum systems

  24. Physics:Quantum Open quantum systems

    25. Statistical mechanics and kinetic theory

  25. Physics:Quantum Statistical mechanics
  26. Physics:Quantum Kinetic theory

    27. Plasma and fusion physics

  27. Physics:Plasma physics (fusion context)
  28. Physics:Tokamak physics
  29. Physics:Tokamak edge physics and recycling asymmetries
    30. Hierarchy of modern physics models showing the progression from quantum statistical mechanics to kinetic theory and plasma physics, culminating in tokamak edge transport and recycling asymmetries.

    Quantum field theory

  30. Physics:Quantum field theory (QFT) basics

    31. Timeline

  31. Physics:Quantum mechanics/Timeline
  32. Physics:Quantum_mechanics/Timeline/Quiz/

    33. Advanced and frontier topics

  33. Physics:Quantum Supersymmetry
  34. Physics:Quantum Black hole thermodynamics
  35. Physics:Quantum Holographic principle
  36. Physics:Quantum gravity
  37. Physics:Quantum De Sitter invariant special relativity
  38. Physics:Quantum Doubly special relativity


References

  1. ↑ 1.0 1.1 J. Wesson, Tokamaks, Oxford University Press.
  2. ↑ J. P. Freidberg, Ideal MHD.
  3. ↑ Emdee, E. D. et al., Combined Influence of Rotation and Scrape-Off Layer Drifts on Recycling Asymmetries in Tokamak Plasmas.


Author: Harold Foppele


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