In regards to the hypothetical Alcubierre Drive (hear me out), are energy costs consumed immediately, or during transit?

Question

I am aware the Alcubierre Drive is highly hypothetical and likely cannot exist.
However, there are significant quantities of research material into Warp Drives of many types, and presumably the answer to my question is out there.
Basically, are energy costs for the Alcubierre Drive / Related Warp Metrics consumed immediately upon "jump to warp" (10kg to jump to 10c) or consumed constantly (10kg per hour at 10c)?
As an additional question, could Alcubierre Metrics potentially be feasible at sub-light speeds of exotic energy exists but quantum instabilities forbid FTL travel. Would such a drive be able to reach light-speed, simply not beyond?
Final optional question; how does cherenkov radiation relate to Alcubierre Drives, FTL or otherwise.

Answer 1

As you say, the Alcubierre metric is a perfectly good solution to the Einstein equations, though since it requires exotic matter to work it doesn't seem likely that one could be built. However it is important to understand that the Alcubierre metric is time independent i.e. it describes the object moving at a constant speed. It does not describe how the object accelerates or how it could slow down after its journey.

For the moving object described by the Alcubierre metric no energy is required, but this shouldn't surprise you. A conventional spacecraft moving through space at a constant speed also doesn't require any energy. Work only need to be done when the spacecraft accelerates or brakes.

If you were to attempt the building of a drive like this presumably you would start with the exotic matter widely spread, and you'd need to bring it together to form the torus that makes the drive. Then when you wanted to stop you would dismantle the torus and disperse the exotic matter again. The energy required would be the energy involved in making then dismantling the torus. However I don't know of any studies done to establish how much energy is needed. Since exotic matter attracts other exotic matter and repels ordinary matter this suggests that building the torus would release energy not consume it. Then dismantling the torus would require energy to be put in. But in the absence of any rigorous calculations the best we can do is speculate.