On Density Limit of Lower Hybrid Current Drive caused by Parametric Decay Instability in Tokamak Plasmas

TL;DR

This paper analyzes how parametric decay instability limits the density for lower hybrid current drive in tokamaks, showing that the limit is higher than operational densities for ITER, supporting LHCD's viability.

Contribution

It presents a theoretical model linking parametric decay instability saturation to the density limit of LHCD, validated by simulations and experiments.

Findings

Density limit scales with plasma and wave parameters as $n_{lim} \,\propto\, L_y^{2/3} P_0^{-2/3} \omega_0^{2} B_0^{2/3} T_e$.

The density limit is well above ITER baseline densities, indicating LHCD remains effective.

Theoretical and simulation results agree, confirming the model's validity.

Abstract

The density limit of lower hybrid current drive (LHCD) is scaled by coupling the saturation process of parametric decay instability induced by LH waves in the scrape off layer (SOL) plasma to the propagation of waves. It is shown that the density limit of LHCD satisfies $n_\text{lim}\propto L_y^{2/3} P_0^{-2/3}\omega_0^{2}B_0^{2/3}T_e$, which is consistent with results of simulations and previous experiments. Both theoretical analysis and simulation results indicate that the density limit is far from being reached for ITER baseline profile. Therefore, the density limit phenomena will not prevent LHCD from being a promising method of driving plasma current at ITER and future tokamaks.