A New Method to Identify the Equilibria Compatible with the Measurements Using the Technique of the ε-Nets

Abstract

In tokamaks, the problem of plasma current density and safety factor reconstruction, given the available measurements, can be strongly unstable with respect to the input data. Different constraints are used in practice to make the problem more stable. Traditionally, methods for equilibrium reconstruction search for one solution of the Grad-Shafranov equation with a set of constraints. However, the questions of the efficiency of a constraint in selecting a solution; the required accuracy of the measurements; the existence of very different solutions, which are compatible with the measurement errors; and the detailed assessment of the reconstruction confidence intervals are not addressed. This paper presents a numerical algorithm, based on the ε-net technique, which provides answers to all these questions. Examples of application of the method to the analysis of ITER- and JET-like plasmas are given.