In order for nuclear fusion to occur, deuterium (heavy hydrogen) must reach a temperature hot enough for one deuterium atom to have high enough kinetic energy to fuse with another deuterium atom, and there also must be a high enough density for there to be high probababilities that the deuterium atoms will collide. In a hydrogen bomb, the only way for the deuterium to achieve those conditions are thru the initial action of a fission bomb which creates the necessary temperatures and pressures for fusion to occur.
If you are not talking about bombs, some fusion reactors are initiated thru mechanisms like high intensity lasers to create the temperatures and densities for fusion. No fusion reactor is currently initiated by fission.
If you are not talking about bombs, some fusion reactors are initiated thru mechanisms like high intensity lasers to create the temperatures and densities for fusion. No fusion reactor is currently initiated by fission.