Cosmas Heiß

We present results from a new Kinetic-Equilibrium Prediction (KEP) workflow and shot preparation for full TCV discharges, by coupling predict-first RAPTOR transport simulations with FBT inverse equilibrium calculations. RAPTOR is a 1.5D transport code which has been extensively used for plasma shot optimization and real-time modeling. We show that rapid pre-shot simulations can be performed directly using information from the pulse schedule across a wide range of plasma shapes and scenarios, given an estimate of the confinement quality factor H98(y,2) and line-averaged density. The resulting p′ and T T ′ profiles are then provided to the pre-shot equilibrium computation performed by FBT — a static free-boundary solver routinely used at TCV — achieving convergence between the two codes in a few iterations. Finally, we show that this coupling, when integrated into the TCV shot preparation, improves the evaluation of the coil currents needed to match the target plasma shape; in particular providing an accurate estimate of critical quantities such as the internal inductance li and normalized pressure βN , giving more realistic information to tokamak operators about the expected pulse behavior and enabling them to adjust the plan correspondingly.

The goal of this work is to develop a simulator for the TCV tokamak that self-consistently includes transport and equilibrium while taking the plant control systems into account. To achieve this, we adapted the Fenix flight simulator that was originally developed for ASDEX Upgrade for use on TCV. The MEQ-FGE free boundary equilibrium code that is widely used for TCV analysis as well as the TCV magnetic controller were coupled to this framework. In addition, a reduced transport model drawing inspiration from earlier RAPTOR modelling for TCV was implemented. Applying this simulator to discharges in the TCV database shows a good agreement of both kinetic and magnetic results with experimental measurements. In particular, it is illustrated how the shape controller is expected to stabilise discharges and it is found that details of the kinetic profiles can be important for the shape and the stability of the equilibrium. This work paves the way to using Fenix for discharge preparation and validation as well as controller development and validation for TCV.

Accurate and rapid simulation of the free boundary tokamak plasma equilibrium evolution is essential for modern plasma control, stability analysis, and scenario development. This paper presents the Free-Boundary Grad-Shafranov Evolutive (FGE) code, a highly flexible and control-oriented solver designed to address the challenges posed by advanced plasma configurations across a range of devices. FGE evolved from the FBT [Hofmann, 1988] and LIUQE [Moret et al., 2015] codes and is part of the MEQ suite, sharing many of the low-level optimized functions. It self-consistently solves the free-boundary Grad-Shafranov equation coupled with circuit equations for external conductors and models for plasma profile evolution. The code implements a fully non-linear, Newton-based framework with multiple, highly optimized solver options, state representations, and residual formulations that enable rapid computation across different simulation setups. A key capability is the self-consistent integration of various 0D and 1D current diffusion equations (CDEs) to model the resistive evolution of the plasma current profile as well as the ability to model plasmas with multiple magnetic axes (Doublets). Furthermore, FGE allows to linearize the plasma dynamics around a given equilibrium to generate a state-space model suitable for controller design and analysis. Numerical studies are presented demonstrating the code's speed of convergence and validating its performance against experimental data. Furthermore, benchmarks against the RAPTOR and KINX codes for profile evolution and vertical growth rate estimates are presented highlighting FGE's capabilities for both prediction and analysis.