  A new global two-fluid electromagnetic turbulence code, CENTORI, has been
developed for the purpose of studying magnetically-confined fusion plasmas on
energy confinement timescales. This code is used to evolve the combined system
of electron and ion fluid equations and Maxwell equations in toroidal
configurations with axisymmetric equilibria. Uniquely, the equilibrium is
co-evolved with the turbulence, and is thus modified by it. CENTORI is
applicable to tokamaks of arbitrary aspect ratio and high plasma beta. A
predictor-corrector, semi-implicit finite difference scheme is used to compute
the time evolution of fluid quantities and fields. Vector operations and the
evaluation of flux surface averages are speeded up by choosing the Jacobian of
the transformation from laboratory to plasma coordinates to be a function of
the equilibrium poloidal magnetic flux. A subroutine, GRASS, is used to
co-evolve the plasma equilibrium by computing the steady-state solutions of a
diffusion equation with a pseudo-time derivative. The code is written in
Fortran 95 and is efficiently parallelized using Message Passing Interface
(MPI). Illustrative examples of output from simulations of a tearing mode in a
large aspect ratio tokamak plasma and of turbulence in an elongated
conventional aspect ratio tokamak plasma are provided.
