Comparing Current Drive Efficiencies from Empirical Models and Higher‐Fidelity Ray‐Tracing Codes for Various Heating Sources*

The performance of confined plasmas in tokamaks is controlled by several factors including the total

current profile which is comprised of several current drives that result from plasma heating

mechanisms. These heating mechanisms include electron‐cyclotron (EC), ion‐cyclotron (IC), lower‐hybrid

(LH), helicon (HC), and neutral‐beam injection (NBI) heating [1]. Ray‐tracing codes, such as TORAY,

GENRAY, NFREYA, NUBEAM, and TORIC, have been used to accurately calculate the current drive

efficiency and deposition location for each heating mechanism. Considering the large computation

resources required for simulating many heating and current drive schemes using ray‐tracing codes while

searching for an optimum plasma scenario of high performance, the need for reduced, surrogate, or

empirical models for the current drive efficiency is necessary during the design phase [2]. In this work

we compare the current efficiencies using empirical models proposed by Tonon [3] and those calculated

in ray‐tracing codes for radio‐frequency heating mechanisms such as ECH, ICH, LHH, and HCH. The

difference between the empirical models and ray‐tracing codes varies with the heating mechanism. A

further study searches for possible adjustments needed for the empirical models to provide comparable

results to more accurate higher‐fidelity the ray‐tracing codes.