  Following the first observation of an astrophysical high-energy neutrino flux
with the IceCube Neutrino Observatory in 2013 and the identification of a first
cosmic high-energy neutrino source in 2017, the detector will be upgraded with
about 700 new advanced optical sensors. This will expand IceCube's capabilities
both at low and high neutrino energies. A large fraction of the upgrade modules
will be multi-PMT Digital Optical Modules, mDOMs, each featuring 24 three-inch
class photomultiplier tubes (PMTs) pointing uniformly in all directions,
thereby providing an almost homogeneous angular coverage. The signal from each
PMT is digitized individually, providing directional information for the
incident photons. Together, the 24 PMTs provide an effective photosensitive
area more than twice than that of the current IceCube optical module. The main
mDOM design challenges arise from the constraints on the module size and power
needed for the 24-channel high-voltage and readout systems. This contribution
presents an mDOM design that meets these challenges and discusses the
sensitivities expected from these modules.
