Here's a simple way to analyse any number of masses doing only one acceleration and the 1st turn. You have to agree to at least this. I realize there's still the 2nd turn or end stop that's not included. But if you don't agree on these two stages we should solve that first.

The system (only accelerator and 1st turn) is actually a rocket firing masses forward (+ve direction) as they come out of the 1st turn and no longer interact with anything.

So it's a rocket firing its engine in the +ve direction. That means it is accelerating in the -ve direction. It makes no difference how the internal details of the engine work. Any rocket will accelerate in the opposite direction to where the engine is pointed.

Right?