A Variant of the Generalized Assignment Problem for Reliable Allocation of Sensor Measurements in a Diagnostic System

Tokamaks are experimental reactors that currently represent the most promising approach to produce electricity by means of the nuclear fusion reactions. In a tokamak a fully ionized gas, called plasma, in which the nuclear reaction occurs, is confined by means of strong magnetic fields. Its performance, physics knowledge and operation safety are significantly affected by several plasma parameters that are controlled by the so called magnetic control system. However, these parameters cannot be directly measured, but they are estimated by the so called magnetic diagnostic, by combining the information from several sensors. More precisely, different combinations of measurements, which may imply also a different quality of the estimation, can be used to infer the same set of plasma parameters. Each acquisition unit should acquire a set of measurements that allows to reconstruct all the plasma parameters that are needed to operate the machine. In this context, it is fundamental to determine an effective assignment of the sensor measurements to the acquisition units, satisfying capacity constraints and, at the same time, maximizing the overall reliability of the magnetic diagnostic system against possible failures of its components. This problem has been tackled in literature as an original variant of the generalized assignment problem. In this work, we provide a description of the problem itself, as well as a presentation of the related formulations. These formulations are then experienced on real-world test cases in order to show their applicability. Such test cases have been derived from the requirements defined for the JET tokamak, which is the world’s largest tokamak currently in operation. We conclude with a discussion on future research perspectives.