A physical model of plasma behavior in a negative tandem mirror reactor (NTMR) is used to explore the potential of this configuration as a reactor utilizing the deuterium-deuterium (DD) fuel cycle. It is found that relatively high values of plasma Q, in the range 15 to 20, may be possible in an NTMR if passive pumping of deeply trapped ions in the end cell is possible. Further, synchrotron radiation and hot electron end losses are dominant and require accurate modelling. If the physics elements of the model are verified by experimental findings, the results show negative tandem mirrors to be superior to their positive mode counterparts for DD burning.