  Toroidal Alfv\'en eigenmodes (TAEs) can transport fusion-born energetic
particles out of the plasma volume, thereby decreasing plasma self-heating
efficiency and possibly damaging reactor walls. Therefore, understanding TAE
destabilisation and identifying saturation mechanisms is crucial to achieving
burning plasma. While TAEs have been studies extensively in the past using
kinetic-MHD codes, here a fully gyrokinetic study is employed which allows for
additional physics. In the case studied, the primary drive mechanism is
identified as the resonance between the magnetic drifts and the TAE, and this
is seen to be disrupted by equilibrium flow shear which can stabilize the mode
by rotating it in the the poloidal plane. It is found that zonal flows do not
play a significant role in the saturation of these TAEs, and there are no
saturation mechanisms present in the local gyrokinetic picture that are able to
saturate the mode at physically relevant transport levels in the case of
TAE-only turbulence. Instead, we confirm that the global profile flattening of
fast-ion density is the key saturation mechanism. The nonlinear excitation of
TAE travelling along the electron diamagnetic direction and its beating with
the ion diamagnetic TAE, resulting in large amplitude oscillations that may
help detect TAEs more easily in tokamaks, is also reported.
