This invention is designed to be a subsystem of a device, a tokamak with walls or plasma facing components of liquid lithium. This approach to constructing the lithium-bearing walls of the tokamak allows the wall to fulfill a necessary function -- helium pumping – for which a complex structure was formerly required. The primary novel feature of the invention is that a permeable wall is used to separate out helium produced as ash by a burning fusion reactor. This would replace the divertor structure and associated pumps in a diverted tokamak. It may shorten the development time for a fusion reactor due to attendant reductions in size and complexity.