An alternator doesn't have just one loop in the rotor. It has many. There is no need to fill in the gaps between voltage peaks, because there is a rotor peak in voltage every few degrees of rotation. (I don't know exactly how many rotors, or how many degrees of rotation.)
If you did want to "fill in the gaps", yes you would use resistors & capacitors. They were called R-C circuits when I went to school...