Arcane surge

The caster channels raw arcane power into the prism where it is magnified and captured until release. After capturing the surge concentration must be maintained until the following round when another spell may be cast and the surge added to the effect. Any spell not exceeding the spell slot used to cast Arcane Surge to a maximum of lvl 5 may be cast after the surge, adding the spell slot to its total casting power. Thus a 3rd lvl Arcane surge followed by a 3rd lvl fireball would be cast as a 6th lvl fireball. 

After casting the second spell, roll a Con save at DC 10 + total spell level or suffer 1 lvl of exhaustion from the effort to control the raw power.