For example, the only time "fusion" is mentioned in aired TOS is in regards to overloading the impulse engines on the Constellation in "The Doomsday Machine". It is not mentioned with the warp engines or matter-antimatter reactors.
If "energizers" and/or "power plants" are colloquialisms for fusion reactors (which is my basic theory) there wouldn't be any need to further address these (and - indeed - add confusion) as "fusion reactors".
It brings back the simpler, explanation:
- Matter and antimatter are annihilated (when integrated ) and the product energy is sent to the crystals.
But the power loss of all major systems in "The Doomsday Machine"
is due to "power failure in main energizers" which affects
- deflector shields
- instant phaser fire
- warp power
- (normal) impulse power (!!!)
According to Spock and after the energizers' failure they rely on "emergency impulse power" (aka auxiliary impulse power). There is no indication, that "emergency" means to add the extra thrust of auxiliary components as Spock's (later) report to Kirk is clear: "Warp drive out. Deflector shields down. Transporter under repair. We are on emergency impulse power
." (i.e. battery power)
The ship has lost its capability for normal impulse power because of the energizers' failure. Either normal impulse power relies on the energy from the m-am reactors (that would be a concept preceeding TMP, "Elaan of Troyious" suggests "no") or
the m-am reactors ("warp power") require (extra) energy from the energizers / fusion reactors just as the impulse drive does for "normal" operation.
Which is interesting since it could be construed that from only the dialogue that intermix has something to do with the impulse engine reactors. In this case it could, depending on your viewpoint.
The novelization of TMP
makes any of my personal preferences obsolete: "Scott could see a familiar flicker of power barely visible in the great intermix chamber - he was also aware of a low, throbbing sound like tightly-leashed thunder. At this power setting, only microscopic amounts of antimatter and matter were entering the intermix chamber, but the annihilation of even a pinhead of matter was sufficient for the impulse power
which the captain would soon request - and which Scotty would grant."
I'd doubt if the microscopic amounts are sufficient to provide impulse thrust and I've come to understood you'll add fusion power reactants to create the necessary thrust.
Apparently, dilithium crystals are nowwhere mentioned, and it is a pet theory of mine that the enigmatic "impulse deflection crystal
" in the impulse engine block does contain the dilithium crystals for power amplification / discharge / conversion.
For impulse drive the m-am energy travels upwards, is converted by the crystals, fusion reactants are added and you get (sublight) thrust.
For warp drive the same path is taken but the converted m-am energy is reflected / deflected down and rerouted at the T-section of the intermix chamber towards the nacelles (pulsed warp drive).
Possibly this concept was too ambitious and by the time of ST II they had fallen back to a more classic approach (hence the main energizer room) before it finally evolved into the TNG "warp core" design (which, by nomenclature, suggests that the impulse drive now has an independent, separate working system).
One last thing. You were wondering about the dialogue in "Tomorrow Is Yesterday"
SPOCK: Except for secondary systems, everything is out, sir. We're on impulse power only.
SPOCK: If Mister Scott is still with us, auxiliaries should be on momentarily. (Uhura is just stirring on the floor) Are you all right, Lieutenant?
(He helps her back to her seat, and the lights come on.)
Compare to "By Any Other Name"
CHEKOV: We made it.
SPOCK: Instruments returning to normal, Captain.
UHURA: All decks report. Damage and casualties.
SCOTT: Several systems out, sir. Operating on emergency backup. None affect flight procedure.
SPOCK: Life support systems sustaining on emergency.
Both cases show a remarkable TOS continuity consistence.
In any crisis situaion the secondary systems apparently have a priority setting to divert power to the propulsion systems, life support power then relies on the batteries.
Apparently this makes a lot of sense as in the case of "Tomorrow Is Yesterday" full life support power would have hardly done them any good - as in July 1969 the ship would have crashed in Nebraska.