Precise stellarator quasi-symmetry can be achieved with electromagnetic coils.

Magnetic fields with quasi-symmetry are known to provide good confinement of charged particles and plasmas, but the extent to which quasi-symmetry can be achieved in practice has remained an open question. Recent work [M. Landreman and E.

Magnetic Fields with Precise Quasisymmetry for Plasma Confinement.

Quasisymmetry is an unusual symmetry that can be present in toroidal magnetic fields, enabling the confinement of charged particles and plasma. Here it is shown that both quasiaxisymmetry and quasihelical symmetry can be achieved to a much higher precision than previously thought over a significant volume, resulting in exceptional confinement. For a 1 Tesla mean field far from axisymmetry (vacuum rotational transform >0.

Universal instability for wavelengths below the ion Larmor scale.

We demonstrate that the universal mode driven by the density gradient in a plasma slab can be absolutely unstable even in the presence of reasonable magnetic shear. Previous studies from the 1970s that reached the opposite conclusion used an eigenmode equation limited to L_{x}≫ρ_{i}, where L_{x} is the scale length of the mode in the radial direction, and ρ_{i} is the ion Larmor radius. Here we instead use a gyrokinetic approach which does not have this same limitation.