Bloodchief Ascension and Traumatize how many times trigger once or all

[pencilpen]

does Bloodchief Ascension trigger for each card that Traumatize sends to graveyard or just triggers once? Because on one hand there are like say 30 cards going to the graveyard so bloodchief should trigger 30 times, but on the other hand traumatize says to put half your library in graveyard so it sounds like one action(rather then same action 30 times) so sounds like bloodcheif ascension will trigger only once?? what is the ruling?

[Kappu1]

Each card will trigger the effect.