Hope people understand what I am saying.

Drawn a diagram:

 

 

So those little red lines are short bursts of lasers,

(or short continuous beam that is perpetual, if possible)

that is limited in distance,

but angled inwards,

so when the ship comes in contact with half the length of these lasers,

it propels forward.

 

that is creating a bias toward increasing speed.

 

it is not one powerful laser that increases speed at one go,

but incrementally increasing per segment ring of the tunnel....

 

this will gradually increase speed in zero gravity?

 

So big as the tunnel loop itself may be,

the hollow inside the tunnel should not be big,

in comparison to the ship,

so to be able to predict the reach of the lasers.

therefore its effect on the ship.

if the distance is too great,

be it short pulse based bursts,

it will create antagonizing speed instead fixed only to helping it increase.