Fusion takes place in a gas of plasma. The plasma must be hot enough that free nuclei break through each other's electrical barriers and fuse. But, it must be contained, otherwise the plasma wouldn't be concentrated enough. Once the plasma touches the container, it cools down. And you can't drop a huge magnetic-field device on somebody along with the plasma, and expect to have it detonate when you want it
This statement is confusing. Plasma is a 4th state of matter, ie: essentially just free electrons in a hyper temperature state.
As for nuclei, that is the plural of nucleus. A part of a cell.
Fusion for the sun in general,and a hydrogen bomb in particular is hydrogen atoms fusing to form helium. This releases tremendous amounts of energy. But in a nuclear bomb this energy is in an uncontrolled state running wild. The reaction eventually dies out. The sun is different because it is more controlled. Magnetic fields hold it in place along with gravity and electron pressure (which resists collapse). But this is beside the point, unless you are looking to harness fusion reactions for energy this magnetic bottle device is fantasy.