Astral Barrage

You create a portal to the cosmos and send asteroids hurtling through it at a creature you can see within range. The target must succeed on a Dexterity saving throw or take 7d6 Bludgeoning damage. You can take a Magic action on subsequent turns to keep the portal open and send asteroids hurtling through it again. The spell ends if you use your action to do anything else. Your Speed is halved until this spell ends.

Using a Higher-Level Spell Slot. The damage increases by 2d6 for each spell slot level above 3.