This image shows the density of lithium ions that were released from a private flux region evaporator as atoms. The red line indicates the outermost magnetic flux surface separating the core plasma from the rest of the tokamak, which is also known as the separatrix. Computer simulations showed the best location for the lithium vapor cave was in the private flux region as evaporating particles would move up higher toward the separatrix before becoming ionized, mitigating heat from the plasma and then carrying it away.

This diagram shows a section of the cave, which would loop around the bottom of the tokamak near the center stack. Liquid lithium would sit in the bottom of the cave before evaporating.