Permanent Magnet Alternator

Normally he alternator will have the magnet in the rotor so there will be a vaying flux in the pole pieces in the stator.
The voltage produced will depend on the rate of change of flux which will be dependant on the rotor speed and the number of turns on the pole pieces. A lot of turns gives a high voltage but the wire will be thin so current capability will be low. A few turns means the wire can be thicker so low voltage but high current.
The power will be the same in each case.

To get more power, get a bigger machine.

Once you have the machine working, you can get different voltages and curent by using a transformer.