Coupling of the Flux Diffusion Equation with the Equilibrium Reconstruction at ASDEX Upgrade

Abstract

Tokamak equilibrium reconstruction can benefit much from internal measurements of the current distribution. In lacking robust internal measurements the reconstruction is ill-posed in the plasma core, not allowing for a sensible estimation of the current distribution.Such deficiencies can be compensated by modelling of the current distribution evolution by employing the current diffusion equation between successive equilibria. A scheme for the coupling of the predictive current diffusion equation with the equilibrium reconstruction from an inverse Grad-Shafranov equilibrium solver minimising a least-squares criterion on measured and modelled data is proposed. The scheme is intended for routine equilibrium analysis shortly after the discharge where all diagnostic data are available. Results from the implementation at ASDEX Upgrade are shown, applied to a reversed-shear plasma with counter-current ECCD and to the start-up phase of the plasma. Results are compared to TRANSP calculations.

Note: Internal diamagnetic flux measurements on ASDEX Upgrade

“…The transport code, TRANSP [11], allows the diamagnetic flux (parameter DFLUX) to be calculated and compared to the experimental measurements . An offline equilibrium reconstruction code (IDE), with pressure constraints including the fast ion contribution, is also used to calculate the diamagnetic flux [12]. An overview of a discharge with constant electron cyclotron resonance heating (ECRH) power and neutral beam injection heating (NBI) power steps is shown in Fig.…”

Three dimensional boundary displacement due to stable ideal kink modes excited by external n = 2 magnetic perturbations

“…(b) and (c) show time traces of the separatrix movements along the LIB LOS from the integrated data analysis equilibrium (IDE)[37] …”

Optimal MSE polarisation angle and q-profile estimation using Kalman filters and the plasma simulator RAPTOR

“…After the initial verification using synthetic measurements, the q-profile of a full AUG discharge is reconstructed using the MSE observer. A shot with low noise MSE signals is analysed, for which a reference equilibria (reconstructed by MSE constrained IDE [11]) is available. IDE is a GS solver, which, apart from being constrained by the measurements, also evolves the poloidal flux diffusion equation in-between consecutive equilibria reconstructions.…”

“…A recently developed approach, similar to the one described in this paper, is implemented in the IDE code [10,11]. In this approach, a Bayesian approach is used to merge diagnostic measurements related to the core current density with a one-step-ahead prediction based on the poloidal flux diffusion equation.…”