It is shown that the error field in a tokamak can be shielded by a flowing liquid metal wall. In particular, a flowing liquid metal wall can prevent resonance amplification of the error field by the plasma near its no-wall stability limit.

The effect of plasma shape on sawtooth oscillations in the DIII-D tokamak plasmas is investigated by comparing discharges with cross-sections shaped like a bean and an oval. The two shapes are designed so that the Mercier instability threshold is reached when the axial safety factor is below unity for the bean and above unity for the oval cross-sections. This allows the role of interchange modes to be differentiated from that of the kink-tearing mode. The differences in the nature of the sawtooth oscillations in the bean and oval discharges are found to be determined primarily by extreme differences in the electron heat transport during the reheat. In both cases, the axial safety factor is found to be near unity following the crash.

A Hamiltonian formulation is constructed for a finite ion Larmor radius fluid model describing ion temperature-gradient driven and drift Kelvin–Helmholtz modes. The Hamiltonian formulation reveals the existence of three invariants obeying detailed conservation properties, corresponding roughly to generalized potential vorticity, internal energy and ion momentum parallel to the magnetic field. These three invariants are added to the energy to form a variational principle that describes coherent structures (CSs), such as monopolar and dipolar vortices or modons. It is suggested that the invariants are responsible for the coherence and longevity of CSs and for their robustness during binary collisions.