Theoretical scaling of the density limit of lower hybrid current drive caused by parametric decay instability

At high plasma density, the lower hybrid current drive (LHCD) system in tokamaks suffers significant efficiency loss caused by parametric decay instability (PDI) induced in the scrape-off layer (SOL) plasma. There, the lower hybrid waves (LHWs) launched from the antenna deposit a large fraction of their power through PDI, leading to the phenomenon of nonlinear density limit of LHCD. In this paper, we present a self-consistent modelling of the power deposition of LHWs in the SOL plasma by coupling PDI to the propagation of LHWs, the power loss of LHCD is evaluated quantitively, and a theoretical scaling of the nonlinear density limit nPDI ∝ P0−2/3Ly-2/3Teω02 B4/30 is acquired.