inspired by https://lemmy.world/post/39777765
Unruh effect should work for any acceleration, including centripetal acceleration of a James Bond-style killer centrifuge/amusement ride. The "thermal bath" experienced by such an observer is composed mainly of photons, but also some elementary particles, in proportion to quantum field coupling strengths or something, coming in as a "particle shower" from the direction of the Rindler event horizon - namely down. The accelerated observer can capture these particles for use later. Did I get it all correct?
Technically it's not really a horizon if it "opens up" allowing you to observe events from the inside afterwards. But of course in any realistic setting (including that experiment) it will open up eventually, so no horizon. But nature doesn't know that it will open up, so maybe it should behave like a horizon until nature knows, resulting in a criteria like you said. I think the criteria is loosely equivalent to saying "the acceleration must change the speed by almost c", so your centrifuge probably wouldn't lead to radiation.
But I really am not sure about any of this. The right way to do this is to actually calculate the mode function. One day when I'm better with QFT and all these stuff I'll try to do it.