Blood Tap

You wrap your hands with necrotic energy and touch a target, ripping through its flesh and sucking up part of its life force. The targeted creature must make a Constitution saving throw. On a fail, the creature takes 1d8 necrotic damage, and you recovers half of the damage in temporary hit points which disappear at the beginning of your next turn. 

The damage of this spell increases by 1d8 when the caster reaches 5th level (2d8), 11th level (3d8) and 17th level (4d8).