Channelburn

Choose one creature you can see within range. They must make a Constitution saving throw. On a failure, for the duration of the spell, when they expend a spell slot they take 1d8 psychic damage for every level of the spell slot expended (minimum 1d8). At the start of their turn, if they are concentrating on a spell they take 1d8 damage for every level of the spell slot used to cast the spell. 

At the end of each of its turns, the target can make another Constitution saving throw. On a success, the spell ends on the target.