IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 38, NO. 9, SEPTEMBER 2010 2465 The Software Architecture of the New Vertical-Stabilization System for the JET Tokamak Teresa Bellizio, Student Member, IEEE, Gianmaria De Tommasi, Member, IEEE, Paul McCullen, André Cabrita Neto, Member, IEEE, Fabio Piccolo, Filippo Sartori, Riccardo Vitelli, Luca Zabeo, and JET-EFDA Contributors * Abstract—The need to improve the performance of modern tokamak operations has led to a further development of the plasma shape and position control systems. In particular, extremely elon- gated plasmas, with high vertical-instability growth rate, are envisaged to reach the required performance for ignition. This request for better performance from the experimentalists’ side has motivated the development of the new vertical-stabilization (VS) system at the JET tokamak, which has been proposed within the Plasma Control Upgrade project. The main aim of the project is to enhance the capabilities of the plasma vertical position control system in order to operate with very highly elongated plasmas in the presence of large perturbations. This paper focuses on the new software architecture of the VS system, which relies on a highly configurable real-time framework. Due to its flexibility, the new VS system executes different control algorithms, and it schedules the one which maximizes the performance in each plasma phase. Index Terms—Plasma vertical stabilization (VS), real-time systems, tokamak control. I. I NTRODUCTION T HE NEED to achieve better performance in present and future tokamak devices [1] has pushed plasma control to gain more and more importance in tokamak engineering (see the recent book [2]). High performances in tokamaks are achieved by plasmas with elongated poloidal cross section 1 (see Manuscript received January 5, 2010; revised April 12, 2010; accepted May 30, 2010. Date of publication July 15, 2010; date of current version September 10, 2010. This work was supported by the European Commu- nities under the Contract of Association between EURATOM and CCFE, ENEA/CREATE, and IST, which was carried out within the framework of the European Fusion Development Agreement. T. Bellizio and G. De Tommasi are with the Associazione EURATOM– ENEA–CREATE, Università di Napoli Federico II, 80125 Napoli, Italy (e-mail: detommas@unina.it). P. McCullen, F. Piccolo, and L. Zabeo are with the EURATOM–CCFE Fusion Association, Culham Science Centre, OX14 3EA Abingdon, U.K. A. C. Neto is with the Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear (IPFN)—Laboratório Associado, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal. F. Sartori is with the Fusion for Energy, 08019 Barcelona, Spain. R. Vitelli is with the Dipartimento di Informatica, Sistemi e Produzione, Università di Roma, Tor Vergata, 00133 Roma, Italy. * See Appendix of F. Romanelli et al., IAEA Fusion Energy Conference 2008 (Proc. 22nd Int. Conf., Geneva, Switzerland). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2010.2053721 1 If Rmax, R min , Zmax, and Z min are, respectively, the maximum and minimum values of the R and Z coordinates along the plasma boundary (see Fig. 1), then the elongation is defined as κ = Z max - Z min Rmax - R min . It follows that for plasmas with circular cross section, κ =1, while for elongated plasmas, κ> 1. Fig. 1. Poloidal cross section of the JET tokamak. In particular, the cross section of the JET pulse #63005 at t = 31 s is shown. This plasma has an elongation κ ∼ = 1.7 and a vertical-instability growth rate greater than 1000. Fig. 1) and magnetic X-point [3, Tutorial 7]. Since such elon- gated plasmas are vertically unstable [4, Sect. 1.1.5], position control on a very fast time scale is clearly an essential feature of those machines. In order to achieve better performances, it necessary to maximize the plasma volume within the available space. It turns out that the ability to control the plasma shape while ensuring good clearance between plasma and the facing components is an essential feature of any magnetic control system. Furthermore, plasma shape and position control in the ITER tokamak [5] will represent a challenge. Indeed, in the ITER tokamak, which is the next step toward the realization of electricity-producing fusion power plants, the target operational scenarios can approach plant controllability limits [6], [7]. The Plasma Control Upgrade (PCU) project [8] has been proposed with the main aim of increasing the capabilities of the JET tokamak vertical stabilization (VS) system [9], [10]. The VS system is one of the most critical systems in a tokamak, as it is responsible for guaranteeing zero plasma vertical velocity (on average). Indeed, the VS controller is designed to vertically stabilize the plasma so that the shape controller can successfully control the plasma position and shape. The feedback signal is the plasma vertical speed. The actuator is the radial field amplifier (RFA) circuit shown in Fig. 2. To avoid saturating the current in the circuit, the VS controller also implements a current control loop. 0093-3813/$26.00 © 2010 IEEE