On a high-speed machine the continuous vibration tends to let a tightened nut gradually rotate back and loosen the bolted joint, so a washer that actively resists this loosening is required.

A spring lock washer is a split ring bent into a slight helix, so as the nut is tightened the washer is flattened and stores spring tension between the nut and the joint face.

This stored spring load keeps a constant axial pressure on the threads so they cannot easily slacken, and the two sharp cut ends of the ring bite into both the nut and the surface to resist the nut turning back under vibration.

These combined actions are exactly what prevents vibration-induced loosening, which is why the spring lock washer suits this situation.

Flat and plain washers only spread the clamping load over a wider area; they have no spring action and cannot stop a nut from backing off.

A taper washer is shaped to sit square on an inclined or tapered flange surface, so it corrects for angle rather than providing any anti-loosening grip, making it unsuitable here.

Hence, the answer is Spring lock washer.