Optimal Antenna Design for the Alborz Tokamak’s Lower Hybrid Current Drive System

An optimal lower hybrid current drive antenna has been designed for the Alborz tokamak using Multiphysics simulations performed in COMSOL. The study systematically investigates the influence of key parameters—including the antenna phasing configuration and radial displacement, along with the scrape-off layer plasma density, which is modeled under electron cyclotron resonance preionization—on the accessibility, and coupling efficiency of lower hybrid waves (LHWs) in the Alborz tokamak. The unique operational characteristics of the Alborz tokamak define a minimum value of N∥crit = 1.59, while the antenna achieves a representative value of N∥ = 3.56 via the optimal phasing configuration of 120 deg, satisfying the LHW accessibility condition. Furthermore, this phasing configuration directs the power spectrum of launched LHWs asymmetrically in one toroidal direction, aligned with the electron ohmic drift, resulting in significantly enhanced power coupling. This is achieved through the attainment of the minimum reflectivity below 10% and maximum directivity of 72% when the plasma density exceeds the cutoff density of 7.44×1016m−3 at the source frequency of 2.45GHz, which is critical for current drive. Additionally, a radial antenna displacement of 2cm, corresponding to the plasma density of 1.2×1017m−3, is identified as optimal, as it achieves the least reflectivity and enhances electric field intensity in the toroidal direction.