  Quasisymmetry (QS), a hidden symmetry of the magnetic field strength, is
known to support nested flux surfaces and provide superior particle confinement
in stellarators. In this work, we study the ideal MHD equilibrium and stability
of high-beta plasma in a large aspect-ratio stellarator. In particular, we show
that the lowest-order description of a near-axisymmetric equilibrium vastly
simplifies the problem of 3D quasisymmetric MHD equilibria, which can be
reduced to a standard elliptic Grad-Shafranov equation for the flux function.
We show that any large aspect-ratio tokamak, deformed periodically in the
vertical direction, is a stellarator with approximate volumetric QS. We discuss
exact analytical solutions and numerical benchmarks. Finally, we discuss the
ideal ballooning and interchange stability of some of our equilibrium
configurations.
