  The linear dynamics of Alfven modes in tokamaks is investigated here by means
of the global gyrokinetic particle-in-cell code NEMORB. The model equations are
shown and the local shear Alfven wave dispersion relation is derived,
recovering the continuous spectrum in the incompressible ideal MHD limit. A
verification and benchmark analysis is performed for continuum modes in a
cylinder and for toroidicity-induced Alfven Eigenmodes. Modes in a
reversed-shear equilibrium are also investigated, and the dependence of the
spatial structure in the poloidal plane on the equilibrium parameters is
described. In particular, a phase-shift in the poloidal angle is found to be
present for modes whose frequency touches the continuum, whereas a radial
symmetry is found to be characteristic of modes in the continuum gap.
