AN utterly useless suggestion... simply consider the calculations for measuring the gauss of a specific coil with an applied current and you may have your answer. http:www.kjmagentics.com have their magnet information which includes a great deal of technical specifications.  You can compare your math with the tech specs on these magnets and adjust accordingly.  You might find that the permanent NeFeB mags are more powerful that some electromags and will produce less heat.

The acceleration should go unchecked unless loaded.

Please don't smite me for saying this, but:  It should not go unchecked, either it will demonstrate hysteresis and become hot, produce heat and looses its magnetic field, or most likely - all of the above, and come to a resting potential where it expends both motion and heat to dissipate Gaussian energy present in the design.

...this is understandable, but not justifiable; the permanent magnets will all start forming links between themselves weather they're next to each other or not.   You should employ shielding which directs the mag field back onto themselves or use a diamagnetic material - like lead, but possibly something else more safe. Your high pressure area will likely link with some other low pressure area, whether its in front of the slot or not.

If you place two like poles together, their field lines will spread apart and form a contortion in the field but they will eventually lead right back to their counterpart end, they can be held close together by placing two opposite poles next to them so that a linking circle forms...like an X shape with to N and to S poles in the inside ..as you can see, the eventual structure forms an area with both north and south poles.  The idea is that the N-S arrangement always forms a N-S arrangement - ad infinitum, and fractal in nature; so long as their is a vector of magnetism, it will have a North and South pole relative to that vector as if it were a virtual cold current.

@spark

If this is right, that you becomes "LOSSES" with heat (!?)
That is GREAT. "SAVE" this heat ! It is Energy and do's not
overheat the magnet.
IF  this runnig "free" AND produce heat. So .. than it is an
"Free heater"   ;-)

So do not smile over this... but never give up ...
Pese