Physics:Quantum Fusion
Nuclear fusion is a process in which two atomic nuclei combine to form a heavier nucleus, releasing energy. Fusion reactions power stars and are the basis for controlled fusion research on Earth.
Fusion is fundamentally a quantum-mechanical process because it relies on quantum tunnelling to overcome the electrostatic repulsion between positively charged nuclei.
Basic mechanism
Classically, two nuclei cannot approach each other due to the Coulomb barrier. However, quantum tunnelling allows particles to penetrate this barrier with a finite probability.
The fusion rate depends on:
- Particle density
- Temperature
- Quantum tunnelling probability
Coulomb barrier
The Coulomb barrier is the electrostatic repulsion between positively charged nuclei. It prevents nuclei from approaching each other at low energies.
In classical physics, fusion would require extremely high temperatures to overcome this barrier. However, quantum tunnelling allows particles to penetrate the barrier even when their kinetic energy is insufficient.
The height of the barrier depends on the charges of the nuclei and their separation distance.
Maxwellian average
In a thermal plasma, particle velocities follow a Maxwell–Boltzmann distribution. The fusion reaction rate depends on the average of the product of cross section and velocity:
This quantity is known as the Maxwellian average and determines the effective fusion rate at a given temperature.
Gamow peak
The Gamow peak represents the most probable energy range at which fusion reactions occur.
It arises from the combination of:
- The Maxwell–Boltzmann distribution (favoring higher energies)
- Quantum tunnelling probability (favoring lower energies)
The resulting peak defines the energy window where fusion reactions are most likely.
Fusion reactions
Common fusion reactions include:
- Deuterium–tritium (D–T)
- Deuterium–deuterium (D–D)
- Proton–proton (stellar fusion)
These reactions release energy according to mass–energy conversion.
Relation to plasma physics
Fusion occurs in high-temperature plasmas where particles have sufficient energy to approach each other.
The conditions required for sustained fusion are described by the Lawson criterion.
Confinement
To achieve fusion, plasma must be confined:
- Magnetic confinement → tokamak
- Inertial confinement
Confinement determines how long particles remain in conditions suitable for fusion.
Physical interpretation
Fusion represents the conversion of mass into energy through nuclear interactions governed by quantum mechanics.
It connects:
- Quantum tunnelling
- Plasma physics
- Energy generation
See also
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