  Nonlinear symmetry breaking may occur in systems with two or more states
whose linear dynamics displays certain symmetries, one of which is preferred
nonlinearly. We have identified a regime of electron temperature gradient (ETG)
instabilities in a tokamak plasma with circular concentric flux surfaces that
has its largest growth rate at a finite ballooning angle, establishing a
symmetry that is nonlinearly broken to favor one sign for the ballooning angle.
This is the first example of nonlinear symmetry breaking in simulations of a
drift instability in the absence of externally imposed flow shear or asymmetry
in the plasma column.
