The AM in the core IS being annihilated isn't it?
Yes, but not instantaneously. If something goes wrong with the containment fields before the antimatter in the core is used up, then you can get an explosion. Presumably that's what a warp core breach
is. It's a breach in the fields that keep the annihilation reaction contained within the warp core.
How is it different from a "controlled explosion" inside, say... an internal combustion engine? What other way is there for it to go out of control other than losing control of the flow of AM into the intermix?
Like I said, a breakdown in the containment fields. The difference is that the gasoline in your car won't blow up just from touching the walls of the engine.
That seems to be going deeper in the tech than has been established anywhere AFAIK. Is there a canon or even speculative non-Trek source that indicates some AM in the mixture isn't being used?
What I'm saying is that it wouldn't be instantaneous. It would take time. Heck, that's the whole point of the "swirl chamber" design in TMP, all those swirling lights inside the whole long shaft. The idea is that the matter and antimatter are mixing all the way along the shaft, a gradual process rather than an instantaneous one.
And that's consistent with the real science of something like this. Subatomic particles are very small. You smash a stream of protons and a stream of antiprotons together, and a lot of them are quite simply going to
miss each other. If you want the majority of the particles and antiparticles to annihilate each other, either you need to focus them insanely accurately (which seems to be part of what dilithium does according to the
TNG Tech Manual) or you need to give them more than one chance to react, let them mix together for a while to maximize the number of particle collisions.
Closer? lol well it's only what a couple hundred meters at most. It's nonsensical to waste that space for a secondary hull section that is useless without the primary hull anyway. Especially for something as trivial as the arboretum or hangar bay. If your main PTS was out for the Primary hull, you have much bigger problems than landing a shuttle and your navigational deflector is worthless since you're not going to be going anywhere.
Haven't you got it backwards? The primary hull is the one that's useless without the secondary hull. Or rather, neither hull is functional without the other. The hangar bay and nav deflector are hardly useless, and if you had to spend five years cooped up in a tin can in space, you'd no doubt rethink your opinion about the importance of the arboretum. (Which, by the way, would no doubt produce a fair amount of the ship's oxygen.)
^ My argument in a nutshell for putting the matter/antimatter reactor in the secondary hull rather than the nacelles.
Eh? It is isn't it?
That's accepted these days, but there were a couple of references in TOS and TAS that suggested otherwise, so it's been a matter of debate in technical fandom for decades.
But
this Doug Drexler cutaway (or essentially the same one) appeared onscreen in ENT: "In a Mirror, Darkly," making it the closest thing we have to a canonical
Constitution-class layout, and it puts the M/ARC in the secondary hull, running beneath the engine room.