The Alcubierre drive is itself a solar system destroyer.
. When activated, space behind an Alcubierre drive expands while
contracting in front. The ship itself hums along in a stable pocket,
or bubble in space. It turns out the bubble is the problem.
As your faster-than-light ship sails through the cosmos, it’s not
alone. Although we often think of space as empty, there are loads of
high-energy particles shooting through the void. The University of
Sydney research indicates that these particles are liable to get
swept up in the craft’s warp field and remain trapped in the stable
bubble. ... The longer the journey lasts, the more of these dangerous
particles build up....
The instant the Alcubierre drive is disengaged, the space-time
gradient that allows it to effectively move faster than light goes
away. All the energetic particles trapped during the journey have to
go somewhere, and the researchers believe they would be blasted
outward in a cone directly in front of the ship. Anyone or anything
waiting for you at the other end of your trip would be destroyed.
Because of a funny little quirk of relativity, there is no upper limit
to the amount of energy a Alcubierre drive could pick up. A long trip
could vaporize entire planets upon your arrival. The researchers are
beginning a new round of number crunching to see how bad the problem
is. It’s possible the deadly particle beam could be projected in all
directions, making Alcubierre drives unworkable. That spiffy warp ship
might make a better weapon than method of transportation.
It has been proposed that peaceful travelers using these drives come out of warp at a safe distance from things that might get annihilated by the plume of particles. Or maybe stop periodically to dislodge accumulated particles in deep space.
If you want your drive to be a weapon, "no upper limit to the amount of energy" is pretty big. Turn their star into supernova with one torpedo. You can do it fast, because these drives are fast. There is no way I can think of to detect an incoming Alcubierre warp bubble.
I can think of only one way to block a blast of incoming particles from a Alcubierre torpedo coming out of warp. I would like to see what readers think of. Encrypt comments with your ideas using ROT13 please so everyone can have fun! https://en.wikipedia.org/wiki/ROT13