Optimization of the operational domain for ICRH scenarios in WEST from statistical analysis

Abstract

In the WEST tokamak, the Ion Cyclotron Resonance Heating (ICRH) system plays a substantial role in increasing the plasma temperature. However, its efficiency can be lowered by two main phenomena: ripple-induced fast ion losses and technical limits on the antenna current. In this work, a new technique using IR thermography was employed to measure the flux of particles coming from the trapping of fast ions in the toroidal magnetic field ripple. These measurements provided the opportunity to fit parametric scaling laws in order to predict the ion flux intensity and the total power loss for experiments with a plasma current of $I_\textrm{p} = 500$ kA and a major radius of the cyclotron resonance layer of $R_\textrm{1H} = 2.5$ m depending on the heating power and the line-averaged electron density. Furthermore, another semi-empirical parametric scaling was developed to evaluate the coupling resistance depending on controllable parameters such as the line averaged electron density and the radial outer gap between the separatrix and the ICRH antenna. These laws were used to define an operational domain from the database of previous experiments made during campaign C4. The settled operational domain suggests that high power ( $P_\textrm{ICRH} \gt 3$ MW) and high electron density ( $\overline{n_\textrm{e}} \gt 5.0\times10^{19}$ m ^−3 ) discharges are suitable for optimized steady-state high confinement scenarios in WEST using ICRH.

Keywords

• scaling law
• fast ions
• ripple
• coupling
• operation
• ICRH