As originally envisioned, the mass driver was intended to launch payloads from a lunar base to L5, the fifth Lagrange point in which a stable orbit can be maintained.
This is where Gerard K. O'Neill proposed building a space colony (of the five Lagrange points, only L4 and L5 are truly stable, both for the real physical Earth/Moon system as well as for the ideal restricted 3-body case).
The bucket rode on four rails made from copper plumbing tubes, through which was fed direct current from several car batteries connected in series.
When the bucket coil was cooled by liquid nitrogen to reduce its electrical resistance, it was able to achieve an acceleration of around 30 g (300 m/s²).
Further development awaits the day when the space launch market off-Earth is large enough to justify the cost.