Abstract. The Ignitor machine can access a wide variety of plasma regimes, thanks to its high magnetic fields and plasma currents and the flexibility of its poloidal magnetic field system, with ``split'' central solenoid, that can produce both extended limiter and divertor-like double X-point configurations. The average poloidal field is maximized to ensure macroscopic plasma stability at ignition. Near ignition, internal modes close to ideal marginal stability are expected to be influenced by nonlinear effects. 3D nonlinear simulation is used to identify the effective threshold. The effects of ellipticity and triangularity on the mode threshold are considered and resistivity and viscosity are included nonlinearly. The BALDUR transport code is used to simulate the approach to ignition when reversed shear conditions with peaked density profiles are produced through appropriate current ramping. The importance of particle density profile control is demonstrated and the optimal auxiliary heating power to accelerate ignition is evaluated. The bifurcation from the neoclassical and turbulent transport due to the reversed magnetic shear and Er-shear is included.