Since they do not exist yet I do not believe they have any other names. Fusion does exist in nature so a sun or star could be considered a fusion reactor.
neither cold fusion nor warp fields exist.
The sun runs on nuclear fusion. No sun and the Earth is just a cold dead rock.
Because of the nuclear fusion that it does.
Plasma
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In what state must matter exist for fusion reactions to take place
fission bomb no, fusion bomb yes.
No. A fusion event requires a much greater energy density than can exist at the Earth's core.
No. only 2 fusions exist that involve necroshade.
You can't. It doesn't exist.
No, you cannot use Fusion Substitute Monsters for "Future Fusion". You can, however, use Fusion Substitute Monsters for "Chain Material" as long as those Fusion Substitute Monsters exist on your field or hand. The reason Fusion Substitute Monsters cannot be used from your deck is because they have no substitute ability while in the deck and thus cannot be used as replacements for other Fusion Material Monsters.