R. Vitelli

Real-time systems in tokamak devices. A case study: The JET tokamak

The achievement of the required performances during the operation of large fusion experimental reactors, is strictly related to the flexibility and reliability of the real-time infrastructures. It turns out that, in tokamak reactors, the real-time infrastructure has to be designed so as to meet a number of common requirements. An overview of the real-time infrastructure currently adopted at the JET tokamak is given in this paper, focusing the attention on the solutions that have been developed for addressing these common requirements. Furthermore, three real-time systems recently deployed at JET are described as example.

A Software Tool for the Design of the Current Limit Avoidance System at the JET Tokamak

A current limit avoidance (CLA) system has been proposed to avoid current saturation in the poloidal field (PF) coils of the Joint European Torus tokamak when the eXtreme Shape Controller is used to control the plasma shape. CLA uses the redundancy of the PF coil system to automatically obtain almost the same plasma shape with a different combination of control currents. This paper describes the set of graphic tools that has been recently developed to aid the design of the CLA parameters by nonexpert users.

An anti-windup-based solution for the low current nonlinearity compensation on the FTU horizontal position controller

In this paper we focus on the nonlinear behavior of the F coil current amplifier at the Frascati Tokamak Upgrade (FTU), which induces closed-loop instability of the horizontal position stabilizing loop whenever the requested current is below a minimum current level. In the paper we first illustrate a modeling phase where nonlinear dynamics are derived and identified to reproduce the open-loop responses measured by the F coil current amplifier. Based on this dynamic model, we then reproduce the closed-loop scenario of the experiment and show that the proposed nonlinear model successfully reproduces the instabilities experienced in the experimental sessions. Next we propose a nonlinear control solution to this instability problem inspired by the so-called anti-windup paradigm. We report on experiments carried out at FTU, testing two versions of the anti-windup solution differing in terms of performance and robustness.

Shape control with the XSC during plasma current ramp-up and ramp-down at the JET tokamak

The eXtreme Shape Controller (XSC) has been originally designed to control the plasma shape at JET during the flat-top phase, when the plasma current has a constant value. During the JET 2012 experimental campaigns, the XSC has been used to improve the shape control during the transient phases of plasma current ramp-up and ramp-down. In order to avoid the saturation of the actuators with these transient phases, a Current Limit Avoidance system (CLA) has been designed and implemented. This paper discusses the CLA algorithm and presents the experimental results achieved at JET during the 2012 campaigns using the XSC.