Erimos's Brilliant Beam

What would initially look like a giant transmutation circle appears in the sky about 10 feet above you, the center of the circle aimed at a target you can see within range. The circle then unleashes a beam of yellow energy at your target. They must make a constitution saving throw or take 20d6 force damage, half on a successful save. Every turn the saving throw is repeated and the base damage of the spell increases by 5d6. (20d6 First Round, 25d6 Second Round, 30d6 Third Round, etc.) Furthermore, if this spell reduces your health to zero, you make a Constitution saving throw or your body is instantly vaporized. While concentrating on this spell you remain stationary in your current location(floating if necessary), are resistant to all forms of damage that are magical and are immune to being knocked prone. If your target breaks line of sight or is vaporized, you must either stop concentrating on the spell or select another target.  This spell emits bright light in a sphere with a radius equal to the distance you are from your current target. Nonmagical structures not made of adamantine also suffer 2x damage from this spell.