| Electron temperature profiles are measured to be strongly peaked in the core of HSX plasmas during electron cyclotron resonance heating at the full field strength of one Tesla. Neoclassical calculations of the ambipolar radial electric field (Er) result in very large fields in the core, with small fields towards the plasma edge. The transition between these solutions results in a region of strong radial Er shear which is predicted to suppress turbulent transport. Coupled with predictive turbulent transport simulations, the neoclassically determined Er profile has been used to explain the peaked temperature profiles as an internal transport barrier (ITB). This represents the first time this type of ITB has been observed in a quasisymmetric device, where it had been predicted to be difficult to achieve. Initial evidence of threshold behavior for achieving the ITB has been observed, consistent with the neoclassically predicted Er profile. The neoclassical analysis is performed using the PENTA code, which includes the effects of collisional momentum conservation and parallel flows. Collisional momentum conservation is known to be important in tokamaks and ideal quasisymmetric stellarators, but is typically neglected for neoclassical calculations in conventional stellarators. By including these effects PENTA can be applied to the full range of configurations, including fully 2D and 3D devices. PENTA has been greatly extended in the course of this work to incorporate the three existing methods of momentum correction using moment methods, and to handle impurity transport modeling. Under current HSX operating conditions, the momentum conserving calculations are shown to have a small effect on the radial fluxes and the ambipolar radial electric field profile, but to significantly change predictions of the bootstrap current and ion parallel flow. The electron bootstrap current at large Er is shown to even change sign when the momentum correction is applied. |
