 Over time, this led to the idea of using the fields to create an internal divertor that flings the heavier elements out of fuel, typically towards the bottom of the reactor.There, a pool of liquid lithium metal is used as a sort of limiter; the particles hit it and are rapidly cooled, remaining in the lithium.This internal pool is much easier to cool, due to its location, and although some lithium atoms are released into the plasma, its very low mass makes it a much smaller problem than even the lightest metals used previously.