  The development of the flat moderator concept at ESS recently opened up the
possibility that a single flat moderator above the target could serve all the
scattering instruments, that rely on high brightness. This would allow for the
introduction of a fundamentally different moderator below the target for the
complementary needs of certain fundamental physics experiments. To facilitate
experiments depending on the total number of neutrons in a sizable beam, the
option of a voluminous D2 moderator, in a large cross-section extraction guide
is discussed and its neutronic performance is assessed.
