  In this paper, we propose a structure for graphene spaser and develop an
electrostatic model for quantizing plasmonic modes. Using this model, one can
analyze any spaser consisting of graphene in the electrostatic regime. The
proposed structure is investigated analytically and the spasing condition is
derived. We show that spasing can occur in some frequencies where the Quality
factor of plasmonic modes is higher than some special minimum value. Finally,
an algorithmic design procedure is proposed, by which one can design the
structure for a given frequency. As an example, a spaser with plasmon energy of
0.1 eV is designed.
