Nonlinear symmetry breaking in electron temperature gradient driven turbulence

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.