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

Tsinghua University, Department of Engineering Physics, 100084 Beijing, China

^* Corresponding author: ky-chen@mail.tsinghua.edu.cn
^** Corresponding author: gaozhe@tsinghua.edu.cn

Published online: 7 January 2026

Abstract

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 n_PDI ∝ P₀^−2/3L_y^-2/3T_eω₀² B^4/3₀ is acquired.