  We characterize the neutron output of a deuterium-deuterium plasma fusion
neutron generator, model 35-DD-W-S, manufactured by NSD/Gradel-Fusion. The
measured energy spectrum is found to be dominated by neutron peaks at 2.2 MeV
and 2.7 MeV. A detailed GEANT4 simulation accurately reproduces the measured
energy spectrum and confirms our understanding of the fusion process in this
generator. Additionally, a contribution of 14.1 MeV neutrons from
deuterium-tritium fusion is found at a level of~$3.5\%$, from tritium produced
in previous deuterium-deuterium reactions. We have measured both the absolute
neutron flux as well as its relative variation on the operational parameters of
the generator. We find the flux to be proportional to voltage $V^{3.32 \pm
0.14}$ and current $I^{0.97 \pm 0.01}$. Further, we have measured the angular
dependence of the neutron emission with respect to the polar angle. We conclude
that it is well described by isotropic production of neutrons within the
cathode field cage.
