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The International Thermonuclear Experimental Reactor (ITER) is the next step toward the realization of electricity-producing fusion power plants, and it is planned to be in operation in 2016. ITER has been designed so as to reach the plasma burning condition and to operate with high-elongated unstable plasmas. However, due to the constraints that affect the machine realization, these open-loop unstable high-performance plasmas can hardly be stabilized using the poloidal field coils placed outside the tokamak vessel. For this reason, during the ITER design review phase, it has been proposed to investigate the possibility of using in-vessel coils in order to improve the best achievable performance of the vertical stabilization (VS) system. This paper proposes a new approach for the plasma current, position, and shape control design in the presence of in-vessel coils. Two control loops are designed: a first loop that guarantees the VS driving the voltage applied to in-vessel coils, and a second loop that controls the plasma current and up to 32 geometrical shape descriptors as close as possible to the reference values. The performance of the proposed control system is shown by means of simulations of some cases of interest. Index Terms--Plasma shape control, plasma vertical stabilization (VS), tokamaks control.

The high-energy ionized particles collected by the divertor structures in a tokamak reactor cause a localized thermal load around the strike-points, which are the intersections of the separatrix with the divertor tiles. To spread on a larger region this thermal load, it is convenient to resort to a sweeping, i.e., a periodical movement of the strike-points. This paper introduces the new model-based sweeping algorithm recently implemented on the Joint European Torus tokamak, within the eXtreme Shape Controller architecture. Index Terms--Plasma-shape control, plasma strike-point sweeping, tokamaks control.

This paper describes a set of graphic tools for the design and validation of the new plasma shape controller [eXtreme Shape Controller (XSC)], which has been recently implemented at the Joint European Torus tokamak. The XSC enables operation with high elongation and high triangularity plasmas. The software suite, which is called XSC Tools, has been developed to automate the design procedure of the XSC. These tools make use of graphic user interfaces to allow the nonspecialist users to prepare for new operative scenarios, without the help from modeling and control specialists. Once a new controller is generated, all its parameters are saved into a text file, which is used to perform the validation of the scenario via simulations. The same file is then loaded by the real-time code running on the plant, without any further processing. This feature guarantees that the controller, which is running on the plant, is exactly the same one validated through simulations. An additional effort has been made in order to make the XSC Tools machine independent, i.e., to enable their use on the different tokamaks. Index Terms--Control-system validation, software tools, tokamak control.

In this note, we consider the filtering [H.sup.[infinity]] problem for linear time-varying systems. This problem has been already solved in the case when the direct feedthrough matrix F between the disturbance and the output vectors is full-row rank. Here, we consider the case when the problem is singular, that is when this feedthrough matrix is not full-row rank. We show that in this case a reduced-order observer can be designed to meet the desired performance. Moreover, we apply the obtained results to solve a particular [H.sup.[infinity]] singular output feedback problem. Index Terms--Filtering, [H.sup.[infinity]] control, time-varying systems.

We focus on the estimation of the minimum poloidal field coil voltages for the plasma shape control in a tokamak. For given coil locations and for a class of disturbances we propose a procedure for the evaluation of the minimum voltages needed to guarantee that the plasma boundary displacement remains within specified limits. The impact of this problem on the minimization of the power supply cost is discussed for the case of the International Thermonuclear Experimental Reactor (ITER). Index terms - Optimization, plasma control, power supplies, tokamaks, electromagnetic fields, finite element methods.

In this paper we consider linear time-varying systems subject to norm bounded, one block, structured uncertainties. First, given an unforced system, we find necessary and sufficient conditions for quadratic stability; then, considered a controlled system, we provide necessary and sufficient conditions for quadratic stabilizability both for the state and the output feedback case.

In this paper we consider a linear discrete-time system depending on a vector of uncertain parameters. Assuming that the system matrix depends on parameters as the ratio of a multiaffine matrix-valued function and a multiaffine polynomial and that the parameters range in a hyper-rectangle, we show that the uncertain system is quadratically stable if and only if the set of vertex systems is quadratically stable. This allows us to state a necessary and sufficient condition for quadratic stability in terms of the solvability of a feasibility problem involving linear matrix inequalities (LMI's). Index Terms - Discrete-time systems, linear systems, quadratic stability, uncertain systems.

The plasma control system (PCS) in a tokamak device is in charge of controlling the evolution of plasma parameters according to prescribed models against uncertainties and disturbances. The PCS accomplishes its mission by receiving data from the diagnostics and by computing in real-time the commands to the actuators that affect the plasma behavior. The design of the ITER PCS includes many different aspects, which are not limited to the design of control algorithms, including the definition of the verification and validation tests for various components and commissioning procedures. Moreover, contributions come from different parties that adopt heterogeneous sources. To homogenize these contributions and to keep track of the PCS life-cycle throughout various design stages, a specific system-engineering approach has been adopted on top of the standard ITER life-cycle and the requirement management process. Such an approach relies on a database (DB) implemented using Enterprise Architect that allows modeling various aspects of the PCS design using SysML. This article gives an overview of the adopted approach and describes the structure and the current content of the PCS DB. [ABSTRACT FROM AUTHOR]

This paper deals with the design of a robust state feedback control law for a class of uncertain linear time varying systems. Uncertainties are assumed to be time varying, in one-block norm bounded form. The proposed state feedback control law guarantees fnite time stability and satisfes a given bound for an integral quadratic cost function. The contribution of this paper is to provide a suffcient condition in terms of differential linear matrix inequalities for the existence and the construction of the proposed robust control law. In particular, the construction of the feedback control law is brought back to a feasibility problem which can be solved inside the convex optimization framework. The effectiveness of the proposed approach is shown by means of the results obtained on a numerical and a physical example. [ABSTRACT FROM AUTHOR]

In this paper we deal with the mixed [ABSTRACT FROM AUTHOR]

In this study, the problem of input-output finite-time stabilisation of linear time-varying systems is dealt with. The classical definition of input-output finite-time stability (IO-FTS) is extended to that one of structured IO-FTS, which allows to incorporate, in the definition of the stabilisation problem, some amplitude constraints on the control input variables. A sufficient condition and a necessary and sufficient condition for structured IO finite-time stabilisation are provided in the case of L∞ and L2 inputs, respectively. Such conditions require the existence of a solution to a certain differential linear matrix inequality. The theory is applied to design the active suspension control system for a two-degree-of-freedom quarter-car model. [ABSTRACT FROM AUTHOR]

This paper proposes an approach aimed at avoiding or mitigating the consequences of a plasma disruption in a tokamak. The control strategy is based on a Disruption Predictive Control (DPC) where the use of a set of disruption predictors could allow actively modification of some plasma parameters when a disruption warning is issued. The DPC approach requires the continuous monitoring of various plasma performance indicators, which play the role of disruption precursors. The active control is based on the availability of magnetic and nonmagnetic plasma parameter response models as well as multivariable control algorithms and architectures. [ABSTRACT FROM AUTHOR]

Tokamaks are the most promising approach for nuclear fusion on earth. They are toroidal machines where the plasma is heated in a ring-shaped vessel and kept away from the vessel by applied magnetic fields. To achieve high performance in tokamaks, plasmas with elongated poloidal cross-section are needed. Such elongated plasmas are vertically unstable, hence position control on a fast time scale is clearly an essential feature for all tokamak devices. In this context the Plasma Control Upgrade project was aimed at increasing the capabilities of the Vertical Stabilization (VS) of the JET tokamak. This paper introduces the new JET VS system and focuses on how the flexibility of this real-time system has been exploited to enlarge its operational limits in terms of maximum controllable disturbance. Eventually, some experimental results achieved during the last experimental campaigns are presented. [ABSTRACT FROM PUBLISHER]

As fieldbus networks are becoming accessible from the Internet, security mechanisms to grant access only to authorized users and to protect data are becoming essential. This paper proposes a formally based approach to the analysis of such systems, both at the security protocols level and at the system architecture level. This multilevel analysis allows the evaluation of the effects of an attack on the overall system, due to security problems that affect the underlying security protocols. A case study on a typical fieldbus security system validates the approach. [ABSTRACT FROM PUBLISHER]

The ITER tokamak (Latin for "the way") is the next step toward the realization of electricity-producing fusion power plants, since it has been designed to reach the plasma burning condition. The Central Safety System for Nuclear Risk (CSS) is the control system in charge to assure nuclear safety for the ITER plant, the personnel, and the environment. Since the CSS is a critical safety system, its validation and commissioning play an important role, and the required level of reliability must be demonstrated. In such a scenario, it is strongly recommended to use modeling and simulation tools since the early design phase. Indeed, mathematical models will help in the definition of the control system requirements. These models can be used for the rapid prototyping of the safety system, and hardware-in-the-loop (HIL) simulations can be performed to assess the performance of the control hardware against a plant simulator. This paper introduces the methodology and the software/hardware architecture used to develop both a CSS prototype and a ITER plant model suitable for the test and validation of this prototype. [ABSTRACT FROM AUTHOR]

Describes the design and experimental validation of a multivariable digital controller for a Tokamak. Linearized model of the plasma confined in a Tokamak; Scope of the controller; Nested loops composing the proposed controller; Improvement of the performance with respect to those obtained with a proportional integral derivative.

Presents an approach for the design of a plasma current and shape feedback control system in a Tokamak. Enlargement of the operating envelope in which the Tokamak can operate without current saturation; Properties of the two feedback loops that comprise the proposed controller structure.