How can nuclear fusion be controlled?
Nuclear fusion is controlled through the use of control rods.
Nuclear reactors contain control rods made of cadmium or boron, both neutron absorbing materials.
Neutrons are produced during nuclear reactions. During chain reactions lots of neutrons are produced and too many of these neutrons can lead the nuclear reactor to an explosive tendency.
Therefore, the control rods and used at regular intervals to absorb a desired number of neutrons.