Validation of equilibrium tools on the COMPASS tokamak

TL;DR

This paper validates and compares several MHD equilibrium tools on the COMPASS tokamak, demonstrating their accuracy and real-time applicability for plasma equilibrium reconstruction and control.

Contribution

It provides a comprehensive benchmarking of EFIT++, FREEBIE, and VacTH, showing their consistency and suitability for experimental analysis and real-time control.

Findings

FREEBIE can compute equilibria consistent with EFIT++ data.

EFIT++ and VacTH can reconstruct equilibria from synthetic data.

VacTH is suitable for real-time plasma boundary reconstruction.

Abstract

Various MHD (magnetohydrodynamic) equilibrium tools, some of which being recently developed or considerably updated, are used on the COMPASS tokamak at IPP Prague. MHD equilibrium is a fundamental property of the tokamak plasma, whose knowledge is required for many diagnostics and modelling tools. Proper benchmarking and validation of equilibrium tools is thus key for interpreting and planning tokamak experiments. We present here benchmarks and comparisons to experimental data of the EFIT++ reconstruction code [L.C. Appel et al., EPS 2006, P2.184], the free-boundary equilibrium code FREEBIE [J.-F. Artaud, S.H. Kim, EPS 2012, P4.023], and a rapid plasma boundary reconstruction code VacTH [B. Faugeras et al., PPCF 56, 114010 (2014)]. We demonstrate that FREEBIE can calculate the equilibrium and corresponding poloidal field (PF) coils currents consistently with EFIT++ reconstructions from experimental data. Both EFIT++ and VacTH can reconstruct equilibria generated by FREEBIE from synthetic, optionally noisy diagnostic data. Hence, VacTH is suitable for real-time control. Optimum reconstruction parameters are estimated.