The name Rapael, spelled that way, is not on the list of Watchers who bred with earth women. The chiefs of them are named in 1 Enoch 6 as Semyaz, Arakeb, Rame'el, Tam'el, Ram'el, Dan'el, Ezeqel, Baraqyal, As'el, Armaros, Batar'el, Anan'el, Zaqe'el, SasomaspWe'el, Kestar'el, Tur'el, Yamayol, and Arazyal. The ones who taught the earth people the forbidden things are named as: Azaz'el, Amasras, Armaros, Baraqiyal, Kokarer'el, Tam'el, Asder'el.
A closer match for the name spelled Rapael would be one of the holy archangels which are named in 1 Enoch 20: Suru'el, Raphael, Raguel, Michael, Saraq'el and Gabriel.