Initial Off-Axis Neutral Beam Checkout and Physics Experiments on DIII-D

Two of the eight neutral beam sources on DIII-D have been modified to allow vertical steering, with the injection angle varying from horizontal to downward at an angle of 16.5 degrees for off-axis deposition. Initial experiments to assess the basic beam functionality, geometry, and confinement were carried out. D$_\alpha$ images of beam into gas and plasma yield beam neutral profiles and are key in assessing beam shape and clipping. Neutron and fast-ion D$_\alpha$ (FIDA) diagnostics verify classical behavior of the off-axis beam ions in MHD-quiescent conditions. An initial physics experiment takes advantage of the downward steered beams to vary the fast-ion gradient $\nabla\beta_f$ from centrally peaked to hollow. Systematic scans determine the stability and impact of reversed shear Alfv\'en eigenmodes and toroidal Alfv\'en eigenmodes as a function of $\nabla\beta_f$.