Alternator

Well, there is an alternator on the ICE. But there are other 'generators' - front brakes trigger a 'regenerator' (my term) on application above ~8 mph, coasting likewise triggers a 'regenerator' when the go pedal is released above ~8 mph.

EDIT: To avoid any confusion, as efusco posted above, there is not a separate alternator such as with a non-hybrid engine, but there is a generator that is part of the HSD. Otherwise, how does the main traction battery get charged?

 

Further clarification: The Prius HSD has two motor-generators, call MG1 and MG2. MG1 is smallish and used to spin the ICE and to transfer power from the ICE to MG2. MG2 is larger and is used as a prime mover and for regenerative braking. Both MG1 and MG2 are sometimes used as electric motors, and sometimes as generators. The electricity generated from MG1 and MG2 is either used to move the car or charge the HV (traction) battery. The small 12V battery, which is like the battery on a "normal" car, is charged from the HV battery by means of a DC to DC converter, which steps down the high voltage to that of the 12V battery. The DC to DC converter also supplies the 12V accessory needs when the Prius is in run mode (lights, radio, MFD, etc.).

Note that this description is simplified a bit, but it gives an accurate idea of how the charging system works.

Tom