Single-stage gradient-based stellarator coil design: optimization for quasi-symmetry on surfaces*

We will present a single-stage approach to optimize current-carrying coils to produce quasisymmetric vacuum magnetic fields on surfaces.  First, we describe a new technique to compute magnetic surfaces in Boozer coordinates.  Then, we optimize for quasisymmetry on these surfaces.  Use gradient-based optimization methods, we can directly optimize the coils to favor quasisymmetry on surfaces.  We will present numerical results that demonstrate the performance of this approach.