DIII-D High Field Side Lower Hybrid Current Drive Experiment: Overview and Status

A high field side lower hybrid current drive (HFS LHCD) system is scheduled for operation in FY23. A 2 MW klystron source has been installed and power testing into water loads will be utilized to verify system operation. The waveguide network is also in progress. The remaining challenges are associated with the in-vessel waveguides and coupler. The waveguides enter on the low field side and follow the vacuum vessel contour up to the center post. The coupler is a compact multijunction with a traveling wave poloidal splitter. The splitter utilizes imbedded RF elements to ensure proper power splitting and minimize reflection. These detailed RF elements were enabled by additive manufacturing techniques and the expected disruption loads and 400C bake compelled the use of a high strength copper alloy, GRCop-84. The system is designed to drive current non-inductively in $\rho\sim$ 0.6 - 0.8, with the driven current density $\sim$ 0.4 MA/m$^2$ in DIII-D AT discharges. The HFS launch position was selected to improve wave penetration and ensure off-axis, single pass absorption. From simulations, good wave penetration is achieved as a result of negligible wavenumber shift until reaching the damping region. The latest simulations, design and system status will be presented.