Dome of Veiled Flames

A translucent purplish dome with a radius of 30 feet appears at a point you choose within 120 feet. When the sphere appears, and as an action on subsequent turns, you can cause it to fill will black and purple flames. Creatures inside the sphere when it fills with flames must succeed on a Dexterity saving throw or take 8d8 fire damage, or half as much on a success. 

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the fire damage increases by 1d8 per spell slot above 5th.