EC absorption efficiency in ITER at one-third nominal magnetic field strength

Abstract

During the first phase of the ITER Pre-Fusion Power Operations (PFPO-1), the Electron Cyclotron Radio Frequency system will be the main heating and current drive source [1]. Evaluations of the L-H power threshold [2] have shown that H-mode is unlikely to be achieved in PFPO-1 scenarios at half-field (B0=2.65T). For this reason, the use of one-third field scenarios in an early phase might help to access H-mode. This means that the EC Heating (ECH) system, with gyrotrons operating at 170 GHz, would then rely on n=3 harmonic resonance. Using a lower frequency, namely 104 GHz, could allow the exploitation of n=2 harmonic resonance, improving heating efficiency and facilitating EC-assisted breakdown which has not been demonstrated yet for n=3 harmonic. This work presents a preliminary evaluation of the performances of an EC system using the two frequencies in a B0=1.8T scenario (obtained by adequately rescaling a reference half-field scenario [3]) via a parametric scan of density/temperature profiles, to cover the range of possible values expected to occur during the operations and provide an estimation of the parameter space region where the use of each frequency allows a good absorption efficiency.