I did the recent (extensive) edit and voted to reopen.
In my view, it is a hard science question, not so different from, say How to create a nuclear explosion localized to only a few square feet?
The thing that makes this one tricky, I think, is the reality-check tag. If it didn't have that, the question would definitely be on topic and a good fit here and not on physics: "I have an idea, what physics do we need to make it work?"
As it stands, I think it's a better fit for physics. But I can see how this question could, with a bit of story padding, be about building a world: "In my world, they use antimatter as power source, and the containment field is going to break. Their system acts like such and such. Is this plausible?" While that might not be a great question, it certainly looks more on topic.
Since antimatter storage is a part of so many sci-fi worlds, I think this is a good look at a possible method to explain how it can work.