How is the use of magnetic fields to plasma related to trying to generate energy using nuclear fusion?

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Explanation:

Fusion is the process of fusing two isotopes of Hydrogen namely Tritium  and Deuterium to produce Helium. To achieve this, tremendous heat required (about a million degrees Celsius). The same for the pressure. To achieve this, the hydrogen is made into a plasma through rarefaction so it becomes susceptible to magnetic fields. Magnetic confinement fusion is an approach to generating thermonuclear fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Electro-Magnets surround the chamber/reactor and are pulsed adiabatically (as in a bicycle pump) and the gas becomes extremely hot that may melt the surroundings.

As the ions in the plasma are charged (the plasma is so hot all the negatively-charged electrons are stripped off the atoms, leaving them with a positive charge) they respond to magnetic fields. Extra fields help shape the plasma and hold it stable.