Presumably the rotor is a series of magnets? Rotate any magnet(s) within a
coil(s) and you can get a form of AC output. DC dynamos have commutators
to give 'pulsed' DC from this. The slip rings in a car alternator are
there so the current in the field windings can be varied thus the output.



No, the rotor is electromagnetic, it looks just like a very large DC
motor armature except it has only two poles and it is entirely self
contained with no electrical connection to any of the stationary parts.
The one diode I can find is mounted in the rotating assembly.