Scoping study of lower hybrid current drive for CFETR

The paper assesses the applicability of lower hybrid current drive (LHCD) for two potentialoperating scenarios for the china fusion engineering test reactor (CFETR): the ‘hybrid’scenario in which some of the plasma current is sustained by the ohmic transformer, and thefully non-inductive ‘steady state’ scenario. The π scope workflow engine was used to set up alarge number of ray tracing/Fokker–Planck simulations (> 104) with parametric scans in theantenna poloidal position and launched parallel refractive index (n) for both the hybrid andsteady state scenarios. Modeling predicts efficient off-axis current drive (1.3 MA for 20 MWlaunched power) with a peak near ρ of 0.6–0.65 for waves launched from the high field side(HFS). Waves launched from the low field side damp at larger radius (ρ > 0.73) with similarefficiency to HFS launch. Stability analysis of the CFETR scenarios favors current driveprofiles peaked near the mid-radius, suggesting that HFS launch is preferable due to the currentdrive location. The effect of wave scattering from density blobs in the edge/scrape-off-layerregion was assessed through rotation of the perpendicular wavenumber at the ray origin.Simulations show that this effect can be quite large both in efficiency and damping location,however by adjusting the launched n much of the unperturbed performance can be recovered.