Quantum Mechanics is the theory that describes the behavior of matter and energy at very small scales where the wave-like properties of matter and the particle-like properties of energy interact. Quantum theory is essential to understand the structure of matter. In focus fusion research, quantum theory is particularly important as it underlies the Quantum Magnetic Field Effect. This effect will reduce the amount of energy emitted as x-rays and make possible the rapid heating up of a hydrogen-boron fuel to the temperature needed for fusion. Prior to LPP’s application to the plasma focus of this effect, discovered years earlier in research in other fields, many scientists thought that the x-ray emission in hydrogen-boron fuel would prevent the ignition of the fuel. That is, they thought the fuel would never reach the point where the heating due to fusion reactions would exceed the cooling due to x-ray emission. But this quantum effect, in the presence of very powerful magnetic fields, reduces the temperature of the electrons, and thus the amount of x-rays that the electrons emit.
For the history of quantum mechanics—see below:
Origins of Quantum Theory
Max Planck—Black Body Radiation and the Discovery of Quanta of Energy
Further history of Quantum Mechanics